摘要:

Highlights of marine natural products chemistry (1972–1999) D. John Faulkner Scripps Institution of Oceanography University of California at San Diego La Jolla CA 92093-0212 USA Received (in Cambridge) 12th November 1999 Covering 1972–1999 1 Highlights of marine natural products chemistry (1972–1999) Marine Natural Products Chemistry is essentially a child of the 1970’s that developed rapidly during the 1980’s and matured in the last decade. With a few notable exceptions it is difficult to select individual papers that significantly impacted the field. However marine natural products chemistry has often influenced other fields and that aspect is the focus of this review. It is clear that the early directions taken by marine natural products chemists drew as much from the examples provided by insect chemical ecology as from the longer history of phytochemistry.By 1975 there were already three parallel tracks in marine natural products chemistry marine toxins marine biomedicinals and marine chemical ecology. It is the integration of the three fields of study that has given marine natural products chemistry its unique character and vigour. Studies of marine toxins have been dominated by Japanese researchers.1,2 Although the structures elucidated have grown larger and larger the polyether structural class remains the basis of a majority of marine toxins. The ‘ladder-like’ skeleton of the polyether toxins was established in 1981 by an X-ray crystallographic study of brevetoxin B 1 from the dinoflagellate Gymnodinium breve.3 Ciguatoxin 2 the principal toxic constituent in ciguateric seafood poisoning was identified in 1989 from material extracted from Pacific moray eels (Gymnothorax javanicus),4 but congeners were isolated from the epiphytic dinoflagellate Gambierdiscus toxicus,5 demonstrating the importance of the marine food chain in seafood poisoning.2 From the same source maitotoxin 3 the largest and possibly the most lethal non-proteinaceous toxin was identified in a tour de force of modern structural elucidation.6,7 Of equal importance and complexity the structural elucidation of palytoxin 4 a complex polyol isolated from the zoanthid Palythoa toxicus provided a classical example of the use of both spectroscopy and synthesis D.John Faulkner born in England in 1942 received his B.Sc.and Ph.D. degrees from Imperial College London where he studied synthetic organic chemistry under the guidance of Sir Derek Barton. He received postdoctoral training from R. B. Woodward at Harvard University and W. S. Johnson at Stanford University before joining the faculty of the Scripps Institution of Oceanography University of California at San Diego in 1968. Recognizing the need to ‘do something more marine’ he began a new career in marine natural products chemistry which has spanned the entire period of this review. He is currently Professor of Marine Chemistry. This journal is © The Royal Society of Chemistry 2000 MILLENNIUM REVIEW in structural elucidation.8–10 Unfortunately the tremendous impact of the palytoxin and maitotoxin studies had the effect of making studies of smaller toxic molecules seem less challenging which is far from the truth.The increasing frequency of toxic algal blooms and the associated shellfish contamination ensures that studies of marine toxins will continue to be of importance well into the next century and probably for as long as human consumption of seafood continues. Research on bioactive compounds from marine organisms has provided the bread and butter support of marine natural products research throughout the past quarter century. Although none of the discoveries has yet led to a pharmaceutical product there is hope that one or more of the many marine natural products currently under investigation will eventually do so.11 Since the current status of marine biomedical research has been a popular subject for many recent reviews,12 just a few examples will be highlighted here.Among the anticancer compounds currently under investigation bryostatin 1 5 serves as a good example of past and current trends in marine biomedical research. Bryostatin 1 5 was isolated in very small quantities from the bryozoan Bugula neritina in the 1970’s and its structure was determined by X-ray crystallography in 1982.13 It is currently in phase 2 clinical trials. Supply of material for clinical trials was a problem until it was demonstrated that B. neritina was amenable to aquaculture. Recently evidence favouring a symbiotic origin for bryostatin 1 5 has been presented,14 opening the way for biotechnological manipulation of the biosynthetic genes.15 Furthermore it has been shown that semi-synthetic bryostatins retain the activity of the natural product.16 Other marine natural products under intense investigation at present include the potential anticancer agents dehydrodidemnin B 6,17 dolastatin 10 7,18 ecteinascidin 743 8,19,20 halichondrin B 9,21 isohomohalichondrin B 10,22 curacin A 11,23 discodermolide 12,24 eleutherobin 1325 and sarcodictyin A 14.26 Marine organisms have also provided a number of antiinflammatory agents such as pseudopterosins A 1527 and E 16,28 topsentin 17,29 debromohymenialdisine 1830 and scytonemin 19,31 all of which are currently under active investigation and manoalide 20,32,33 which has become a standard drug in inflammation research.An interesting commercial application of a marine product is the use of a partially purified extract of the gorgonian coral Pseudopterogorgia elisabethae the source of the pseudopterosins as an additive in cosmetic products. In addition to those compounds being considered for medicinal use there are an increasing number of compounds that are currently used as reagents in cellular biology. Examples include the sponge metabolites swinholide A 21,34 jaspamide 22,35,36 and others that act on actin ilimaquinone 23,37 which causes vesiculation of the Golgi,38 and adociasulfate 2 24,39 an inhibitor of motor proteins,40 as well as those compounds too many to list that act on individual proteins and receptors.Marine natural products chemists have always shown a great interest in the natural functions of the metabolites that they study. Compounds such as stypoldione 25 from the brown alga Stypopodium zonale41 and latrunculin A 26 from the sponge Latrunculia magnifica42 were discovered on the basis of their ichthyotoxicity and were later shown to be cytotoxic. However there are many more subtle ways in which chemicals produced by marine organisms can enhance the survival of the producing 1 Nat. Prod. Rep. 2000 17 1–6 hare Aplysia californica44 and that the sesquiterpene isonitrile 28 isolated from the nudibranch Phyllidea varicosa was a metabolite of the sponge Hymeniacidon sp.,45 led to the hypothesis that the shell-less molluscs had evolved by loss of the shell after the ancestral mollusc had acquired defensive organism.Studies of the feeding deterrence caused by algal metabolites have established chemical defense as an important factor in reducing predation.43 The discovery that red algal metabolites such as the polyhalogenated monoterpene 27 were selectively stored in the midgut gland and the skin of the sea Nat. Prod. Rep. 2000 17 1–6 2 chemicals of dietary origin.46 The observation that many nudibranchs sequestered metabolites of sponges and tunicates implied that these constituted chemical defenses of the producing organisms a hypothesis that is currently being tested.47 Another rationale for chemical production in sessile organisms is that the metabolites inhibit settling of fouling organisms.This hypothesis has also been tested48 but the objective of using natural antifouling agents in marine coatings has yet to be realized. During the past decade many authors have acknowledged the importance of symbiosis in the marine environment and have speculated that key marine natural products were produced by symbiotic microorganisms. Although most claims lacked experimental support two metabolites of the lithistid sponge Theonella swinhoei swinholide A 21 and the cyclic peptide theopalauamide 29 were shown to be localized in a mixed bacterial fraction and a filamentous d-proteobacterium respectively. 49 Although most bacterial symbionts have defied attempts to culture them cultures of the dinoflagellate Amphidinium sp.which is a symbiont of the flatworm Amphiscolops sp. have yielded a series of very cytotoxic macrolides such as amphidinolide B 30.50 Marine organisms have provided a seemingly endless parade of novel structures. New carbon skeletons too many to be highlighted here were described with a frequency that exceeded all expectations. Several functional groups are uniquely or predominantly marine. In the early years chemists were fascinated by the small polyhalogenated compounds such as 27,51 most of which have still defied synthesis. The carbonimidic dichloride functionality of 31 and the sulfamate group in haplosamate A 32 have only been found in nature as metabolites of marine sponges.52,53 Sesquiterpene or diterpene isonitriles isothiocyanates thiocyanates and formamides exemplified by isonitrile 28 are predominantly produced by sponges.Biosynthetic studies have shown that the isonitrile carbons in diisocyanoadociane 33 can be derived from cyanide and thiocyanate ions but some details of the pathway remain 3 Nat. Prod. Rep. 2000 17 1–6 unclear.54,55 An interesting hypothesis concerning the biosynthesis of manzamine A 34 has stimulated research on related alkaloids that can be derived from cyclic bis-pyridine derivatives. 56 Unusual cyclic peptides represented by ulithiacyclamide 35 from the tunicate Lissoclinum patella,57 theonellamide F 36 from Theonella swinhoei58 and diazonamide 37 from the tunicate Diazona chinensis59 are frequently found in many marine phyla.Sesterterpenes originally found in Ircinia oros,60 represent a major group of sponge metabolites but are less often found elsewhere. These are but a few examples of the novelty of marine natural products. Nat. Prod. Rep. 2000 17 1–6 4 Although it is clear that marine natural products chemistry has had a major impact on chemistry over the past 25 years it is difficult to predict the future. Researchers are in a race to discover the biochemical diversity of a marine environment that is increasingly being degraded by natural and human acts of destruction. Fortunately the tools used to identify marine able effort to the genetic engineering required to produce unique metabolites by fermentation of genetically-modified microbes. This will accomplish the goal of having the marine organisms provide the inspiration for new compounds while avoiding their excessive harvesting.References 1 J. Kobayashi and M. Ishibashi in Comprehensive Natural Products Chemistry Volume 8 ed. K. Mori Pergamon Oxford 1999 pp. 476–520. 2 T. Yasumoto and M. Murata Chem. Rev. 1993 93 1897. 3 Y.-Y. Lin M. Risk S. M. Ray D. Van Engen J. Clardy J. Golik J. C. James and K. Nakanishi J. Am. Chem. Soc. 1981 103 6773. 4 M. Murata A.-M. Legrand Y. Ishibashi and T. Yasumoto J. Am. Chem. Soc. 1989 111 8927. 5 M. Murata A. M. Legrand Y. Ishibashi M. Fukui and T. Yasumoto J. Am. Chem. Soc. 1990 112 4380. 6 M. Murata H. Nakoi T. Iwashita S. Matsunaga M. Sasaki A. Yokoyama and T. Yasumoto J. Am. Chem. Soc.1993 115 2060. 7 T. Nonomura M. Sasaki N. Matsumori M. Miata K. Tachibana and T. Yasumoto Angew. Chem. Int. Ed. Engl. 1996 35 1675. 8 R. E. Moore and G. Bertolini J. Am. Chem. Soc. 1981 103 2491. 9 D. Uemura K. Ueda and Y. Hirata J. Am. Chem. Soc. 1981 103 2781. 10 R. W. Armstrong J.-M. Beau S. H. Cheon W. J. Christ H. Fujioka W.- H. Ham L. D. Hawkins H. Jin S. H. Kang Y. Kishi M. J. Martinelli W. W. McWhorter M. Mizuno M. Nakata A. E. Stutz F. X. Talamas M. Taniguchi J. A. Tino K. Ueda J. Uenishi J. B. White and M. Yonaga J. Am. Chem. Soc. 1989 111 7350. 11 R. G. Kerr and S. S. Kerr Expert Opin. Ther. Pat. 1999 9 1207. 12 See for example M. Jaspars Chem. Ind. 1999 51. 13 G. R. Pettit C. L. Herald D. L. Doubek D. L. Herald E. Arnold and J. Clardy J.Am. Chem. Soc. 1982 104 6846. 14 M. G. Haygood and S. K. Davidson Appl. Env. Microbiol. 1997 63 4612. 15 M. G. Haygood E. W. Schmidt S. K. Davidson and D. J. Faulkner J. Mol. Microbiol. Biotechnol. 1999 1 33. 16 P. A. Wender J. De Brabander P. G. Harran J.-M. Jiminez M. T. F. Koehler B. Lippa C.-M. Park and M. Shiozaki J. Am. Chem. Soc. 1998 120 4534. 17 R. Sakai K. L. Rinehart V. Kishore B. Kundu G. Faircloth J. B. Gloer J. R. Carney M. Namikoshi F. Sun R. G. Hughes Jr. D. G. Grávalos T. G. de Quesada G. R. Wilson and R. M. Heid J. Med. Chem. 1996 39 2819. 18 G. R. Pettit Y. Kamano C. L. Herald A. A. Tuinman F. E. Boettner H. Kizu J. M. Schmidt L. Baczynskyj K. B. Tomer and R. Bontems J. Am. Chem. Soc. 1987 109 6883. 19 A. E. Wright D.A. Forleo G. P. Gunawardana S. P. Gunasekera F. E. Koehn and O. J. McConnell J. Org. Chem. 1990 55 4508. 20 K. L. Rinehart T. G. Holt N. L. Fregeau J. G. Stroh P. A. Kiefer F. Sun L. H. Li and D. G. Martin J. Org. Chem. 1990 55 4512. 21 Y. Hirata and D. Uemura Pure Appl. Chem. 1986 58 701. 22 M. Litaudon J. B. Hart J. W. Blunt R. J. Lake and M. H. G. Munro Tetrahedron Lett. 1994 35 9435. 23 W. H. Gerwick P. J. Proteau D. G. Nagle E. Hamel A. Blokhin and D. L. Slate J. Org. Chem. 1994 59 1243. 24 S. P. Gunasekera M. Gunasekera R. E. Longley and G. K. Schulte J. Org. Chem. 1990 55 4912. 25 T. Lindel P. R. Jensen W. Fenical B. H. Long A. M. Casazza J. Carboni and C. R. Fairchild J. Am. Chem. Soc. 1997 119 8744. 26 M. D’Ambrosio A. Guerriero and F.Pietra Helv. Chim. Acta 1987 70 2019. 27 S. A. Look W. Fenical G. K. Matsumoto and J. Clardy J. Org. Chem. 1986 51 5141. metabolites are constantly improving in scope and sensitivity allowing the contents of single organisms to be examined. In addition it seems quite possible that we will soon be able to transfer biosynthetic genes from one organism to another. Thus one might imagine the marine natural products chemist of 2025 still involved in structural elucidation but devoting consider- 5 Nat. Prod. Rep. 2000 17 1–6 28 V. Roussis Z. Wu W. Fenical S. A. Strobel G. D. Van Duyne and J. Clardy J. Org. Chem. 1990 55 4916. 29 K. Bartik J.-C. Braekman D. Daloze C. Stoller J. Huysecom G. Vandevyver and P. Ottinger Can. J. Chem. 1987 65 2118.30 G. W. Sharma J. S. Buyer and M. W. Pomerantz J. Chem. Soc. Chem. Commun. 1980 435. 31 P. J. Proteau W. H. Gerwick F. Garcia-Pichel and R. W. Castenholz Experientia 1993 49 825. 32 E. D. de Silva and P. J. Scheuer Tetrahedron Lett. 1980 21 1611. 33 B. C. M. Potts D. J. Faulkner M. S. de Carvalho and R. S. Jacobs J. Am. Chem. Soc. 1992 114 5093. 34 I. Kitagawa M. Kobayashi T. Katori M. Yamashita J. Tanaka M. Doi and T. Ishida J. Am. Chem. Soc. 1990 112 3710. 35 T. M. Zabriskie J. A. Klocke C. M. Ireland A. H. Marcus T. F. Molinski D. J. Faulkner C. Xu and J. Clardy J. Am. Chem. Soc. 1986 108 3123. 36 P. Crews L. V. Manes and M. Boehler Tetrahedron Lett. 1986 27 2797. 37 R. T. Luibrand T. R. Erdman J. J. Vollmer P. J. Scheuer J. Finer and J.Clardy Tetrahedron 1979 35 609. 38 P. A. Takizawa J. K. Yucel B. Viet D. J. Faulkner T. Deerinck G. Soto M. Ellisman and V. Malhotra Cell 1993 73 1079. 39 C. L. Blackburn C. Hopmann R. Sakowicz M. S. Berdelis and L. S. B. Goldstein J. Org. Chem. 1999 64 5565. 40 R. Sakowicz M. S. Berdelis K. Ray C. L. Blackburn C. Hopmann D. J. Faulkner and L. S. B. Goldstein Science 1998 280 292. 41 W. H. Gerwick W. Fenical N. Fritsch and J. Clardy Tetrahedron Lett. 1979 145. 42 I. Spector N. R. Shochet Y. Kashman and A. Groweiss Science 1983 219 493. 43 M. E. Hay J. Exp. Mar. Biol. Ecol. 1996 200 103. Nat. Prod. Rep. 2000 17 1–6 6 44 M. O. Stallard and D. J. Faulkner Comp. Biochem. Physiol. B Comp. Biochem. 1974 49 25. 45 M. R. Hagedone B. J.Burreson and P. J. Scheuer Helv. Chim. Acta 1979 62 2484. 46 D. J. Faulkner and M. T. Ghiselin Mar. Ecol. Prog. Ser. 1983 13 295. 47 J. R. Pawlik B. Chanas R. J. Toonen and W. Fenical Mar. Ecol. Prog. Ser. 1995 127 183. 48 N. Fusetani Curr. Org. Chem. 1997 1 127. 49 C. A. Bewley N. D. Holland and D. J. Faulkner Experientia 1996 52 716. 50 M. Ishibashi and J. Kobayashi Heterocycles 1997 44 543. 51 D. J. Faulkner M. O. Stallard J. Fayos and J. Clardy J. Am. Chem. Soc. 1973 95 3413. 52 S. J. Wratten and D. J. Faulkner J. Am. Chem. Soc. 1977 99 7367. 53 A. Qureshi and D. J. Faulkner Tetrahedron 1999 55 8323. 54 C. J. R. Fookes M. J. Garson J. K. MacLeod B. W. Skelton and A. H. White J. Chem. Soc. Perkin Trans. 1 1988 1003. 55 J. S. Simpson and M. J. Garson Tetrahedron Lett. 1999 40 3909. 56 J. E. Baldwin and R. C. Whitehead Tetrahedron Lett. 1992 33 2059. 57 C. Ireland and P. J. Scheuer J. Am. Chem. Soc. 1980 102 5688. 58 S. Matsunaga N. Fusetani K. Hashimoto and M. Walchli J. Am. Chem. Soc. 1989 111 2585. 59 N. Lindquist W. Fenical G. D. Van Duyne and J. Clardy J. Am. Chem. Soc. 1991 113 2303. 60 G. Cimino S. De Stefano L. Minale and E. Fattorusso Tetrahedron 1972 28 333. Review a909113k

ISSN:0265-0568    

DOI:10.1039/a909113k

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Marine natural products D. John Faulkner Scripps Institution of Oceanography University of California at San Diego La Jolla CA 92093-0212 USA Received 1st September 1999 Covering 1998 Previous review 1999 16 155 1 Introduction 2 Marine microorganisms and phytoplankton 3 Green algae 4 Brown algae 5 Red algae 6 Sponges 7 Coelenterates 8 Bryozoans 9 Molluscs 10 Tunicates (ascidians) 11 Echinoderms 12 Miscellaneous 13 References 1 Introduction This Report is a review of the literature of marine natural product chemistry for 1998. Earlier reports published in this journal cover the period from 1977 to December 1997. Compared with the research activity reported during 1997,1 the major difference in 1998 was reflected in a shift in interest from marine bacteria to fungi of marine origins.Once again the literature is dominated by reports of sponge metabolites but the excessive speculation regarding possible microbial origins for these metabolites is gradually being replaced by experimental studies. Interest in the synthesis of marine natural products continues to rise and there have been many studies of the pharmacological and biochemical mechanisms of action of marine metabolites. The continued interest in marine natural products chemistry from outside of the field bodes well for its continued development. The format for this review is identical to that of its immediate predecessors. The review does not provide a comprehensive coverage of all research involving chemicals from marine organisms but concentrates on reports of novel marine natural products with interesting biological and pharmaceutical properties.Biochemical studies involving marine organisms studies of the biosynthesis of marine natural products and reports of primary metabolites are specifically omitted. Wherever possible the biological and pharmacological properties of new marine natural products have been reported but unless a new compound is highlighted papers detailing the pharmacological studies are considered to be beyond the scope of this review. In the area of synthetic organic chemistry the review focusses on reports of the total synthesis of marine natural products that confirm or redefine chemical structures. No attempt has been made to review the patent literature or conference abstracts although experience has shown that these are very important sources for those seeking new structures for synthesis.A number of rather specialized reviews appeared in 1998. The most general and probably the most useful of these covers ‘Sulfated compounds from marine organisms’.2 Specific groups of compounds were reviewed in ‘The structural chemistry reactivity and total synthesis of dolabellane diterpenes’,3 ‘Survey of oxygenated 2,11-cyclized cembranoids of marine This journal is © The Royal Society of Chemistry 2000 origin’4 and ‘Biomimetic and synthetic approaches to marine sponge alkaloids derived from bis-pyridine macrocycles’,5 while specific groups of organisms provided the focus for ‘Lithistid sponges star performers or hosts to the stars’,6 Chemical and biological aspects of the sponge genus Dysidea’7 and ‘Advances in chemical studies on low-molecular weight metabolites of marine fungi’.8 Specialists will appreciate reviews of ‘The Fusetani Biofouling Project’,9 ‘Synthesis of marine natural products in Brazil’,10 ‘Cultivation of marine sponges for metabolite production applications for biotechnology?’, 11 ‘Chemical defense and evolution in the Sacoglossa (Mollusca Gastropoda Opisthobranchia)’,12 and ‘Bioassays with marine and freshwater macroorganisms’.13 2 Marine microorganisms and phytoplankton An anticipated bloom of bioactive metabolites from marine bacteria did not occur during 1998 and in fact the number of new marine bacterial metabolites appears to be in decline.Furthermore the ambition of culturing symbionts that produce bioactive compounds ascribed to host invertebrates has yet to be fully realised. None of the bacterial strains isolated from the sponge Suberea creba produced the brominated metabolites of the sponge and none of the metabolites which included 2-nheptyl-1,2,4-trihydroxyquinoline 1 from a pseudomonad isolated from the sponge could be detected in an extract of the sponge.14 The topoisomerase I inhibitors from a Streptomyces sp. KM86-9B cultured from liquid expelled by squeezing an unidentified sponge were identified as a series of iso- and anteiso-fatty acids.15 A sulfonic acid analogue 2 of ceramide was the major extractable lipid of Cyclobacterium marinus.16 7 Nat.Prod. Rep. 2000 17 7–55 The anthranilamide 3 which was isolated from a marine Streptomyces sp. B7747 derived from sediment from the Gulf of Mexico is a phytotoxic antimicroalgal agent.17 A Streptomyces sp. BD-18T(41) isolated from a shallow water sediment on Oahu produced four new quinones halawanones A–D 4–7,18 together with the known bacterial metabolite nanaomycin D.19 Guaymasol 8 and epiguaymasol 9 were obtained from a Bacillus sp. CNA-995 from a deep-sea sediment core.20 A strain of Micrococcus luteus that was cultured from the surface of the Indo-Pacific sponge Xestospongia sp. produced 2,4,4A-trichloro-2A-hydroxydiphenyl ether 10 which had previously been synthesized,21 and an acyl-1-(acyl-6A-mannobiosyl)-3-glycerol 11.22 Two marine Agrobacterium strains that were isolated from tunicates produced sesbanimide antibiotics that had previously been isolated from seeds of the leguminous plants Sesbania drummondii and S.punicea:23 strain PH-130 from Ecteinascidia turbinata produced sesbanamide A 12 and strain PH-A034C from a Polycitonidae sp. contained sesbanamide C 13.24 Three diketopiperazines one of which cyclo[l-(4-hydroxyprolinyl)- d-leucine] 14 was previously undescribed were isolated as plant growth promotors from a marine bacterium A108 associated with a species of Palythoa.25 A Blastobacter sp. SANK 71894 isolated from seawater in Japan produced B- 90063 15 which inhibited endothelin converting enzyme.26 A strategy that employed Stille cross-coupling chemistry was used to prepare the antiviral agent (2)-macrolactin A 16 Nat.Prod. Rep. 2000 17 7–55 8 (+)-macrolactin E 17 and (2)-macrolactic acid 18,27 all of which had been isolated from an unidentified deep-sea bacterium.28,29 Macrolactin A 16 was also synthesized by a route that employed enantioselective dienolate aldol addition reactions.30 The structure and stereochemistry of (+)-pericosine B 19 which was obtained from a strain of Periconia byssoides cultured from the gastrointestinal tract of the sea hare Aplysia kurodai,31 have been confirmed by total synthesis.32 The siderophore alterobactin A 20 from Alteromonas lutoviolacea33 has been synthesized in an efficient manner.34 A highly diastereoselective asymmetric synthesis of moiramide B 21 which is a pseudopeptide from Pseudomonas fluorescens,35 has been reported.36 Pentabromopseudilin 22 which is an antimicrobial agent from Pseudomonas bromoutilis37 and other marine bacteria,38,39 was synthesized to illustrate a [3+2] cycloaddition strategy for the synthesis of nitrogen heterocycles.40 There has been a considerable increase in the number of metabolites reported from fungi that were isolated from the marine environment. However the debate concerning their classification as “marine” continues. While fungal colonies have clearly been documented on the surface of marine algae and sea grasses there is a clear need to demonstrate that fungi grow within sponges and other invertebrates. A marine isolate of the fungus Aspergillus versicolor that was isolated from the surface of the green alga Penicillus capitatus yielded four sesquiterpenoid nitrobenzoyl esters 23–26 the most abundant of which 9a,14-dihydroxy-6b-p-nitrobenzoylcinnamolide 23, showed significant cytotoxicity against the HCT-116 cell line and moderately selective cytotoxicity against a panel of renal tumor cell lines.41 Four tricyclic sesquiterpenes hirsutanols A– C 27–29 and ent-gloeosteretriol 30 were obtained from an unidentified fungus 95-1005C cultured from an Indo-Pacific sponge of the genus Haliclona.42 Isolation of the related sesquiterpene hisutanol D 31 from the terrestrial fungus Coriolus consors shows that similar metabolites can be expected from fungi irrespective of their origin.42 A Fusarium sp.strain CNC-477 which was isolated from a driftwood sample collected in a mangrove habitat in the Bahamas produced the sesterterpenoids neomanginols A–C 32–34 of which 32 and 33 were cytotoxic.43 Trichodenones A–C 35–37 are cytotoxic agents that were obtained together with harzialactones A 38 and B 39 and Rmevalonolactone from the culture broth of Trichoderma harzianum OUPS-N115 that was originally isolated from the sponge Halichondria okadai.44 The fungus Corollospora pulchella which was cultured from driftwood collected in Peleliu yielded the simple lactam pulchellalactam 40 which inhibited CD45 protein tyrosine phosphatase.45 A strain of Penicillium waksmanii OUPS-N133 that was cultured from the brown alga Sargassum ringgoldianum produced pyrenocines D 41 and E 42 of which the latter inhibited P388 leukemia cells.46 Three additional antialgal agents solanapyrones E–G 43–45 were isolated from an unidentified marine fungus CNC-159 that was cultured from the surface of the green alga Halimeda monile.47 Deoxynortrichoharzin 46 was obtained from a saltwater culture of Paecilomyces cf.javanica that was isolated from the sponge Jaspis cf. coriacea.48 The Penicillium sp. strain OUPS-79 which was originally isolated from the marine alga Enteromorpha intestinalis has yielded four additional cytotoxic agents penostatins F–I 47–50 when grown on a different culture medium.49 Epoxysorbicillinol 51 was obtained together with a known metabolite from a saltwater culture of Trichoderma longibrachiatum that was isolated from the sponge Haliclona sp.50 The simple phthalide corollosporine 52 was obtained from Corollospora maritima which is commonly found on rotting algae and driftwood.51 A Penicillium sp.N115501 from a Japanese marine sediment produced the antimicrobial anthranilamide derivative N115501A 53.52 Gymnastatins A–E 54–58 which show significant activity against P388 cells are unusual cytotoxic agents from a strain of Gymnascella dankaliensis that 9 Nat. Prod. Rep. 2000 17 7–55 had been cultured from the sponge Halichondria japonica.53 The same strain of G. dankaliensis contained two unusual cytotoxic sterol derivatives gymnasterones A 59 and B 60.54 Hypoxylon oceanicum LL-15G256 contained two antifungal macrocyclic polylactones 15G256g 61 and 15G256d 62 which had previously been reported from terrestrial fungi,55 and the antifungal lipodepsipeptide 15G256e 63 which contained the Nat.Prod. Rep. 2000 17 7–55 10 rare amino acid b-ketotryptophan.56 Aspergillamides A 64 and B 65 are cytotoxic tripeptides from an Aspergillus sp. that was cultured from a saline lake sediment in the Bahamas.57 Interestingly aspergillamide A 64 consists of a 1:1 mixture of cis and trans rotational isomers about the amide bond marked (*).57 A marine fungus of the genus Scytalidium produced two cyclic depsipeptides exumolides A 66 and B 67 that inhibit the growth of the unicellular alga Dunaliella sp. at 20 mg mL21.58 Mactanamide 68 is a fungistatic diketopiperazine produced by an Aspergillus sp.that was obtained from a brown alga Sargassum sp. from the Philippines.59 The marine yeast Aureobasidium pullulans which was cultured from an unidentified Okinawan sponge produced two diketopiperazines 69 and 70 and orcinotriol 71.60 Tryprostatins A 72 and B 73 which are cytotoxic diketopiperazines from Aspergillus fumigatus strain BM 939,61 together with their enantiomers have been synthesized in a relatively straightforward manner.62 The macroscopic cyanobacteria (blue-green algae) Lyngbya majuscula continues to provide interesting new bioactive metabolites. A specimen from St. Croix contained an additional member of the “curacin family” namely the antimitotic agent curacin D 74.63 An additional synthesis of curacin A 75 which is a potent antimitotic agent from a specimen of L.majuscula from Curaçao,64 has been accomplished in a concise manner.65 A collection of L. majuscula from Grenada produced the cyclopropane-containing fatty acid metabolites grenadadiene 76 which gave an interesting cytotoxicity profile debromogrenadadiene 77 and grenadamide 78 which showed modest cannabinoid receptor binding activity.66 Kalkipyrone 79 is a toxin from an assemblage of L. majuscula and Tolypothrix sp. collected in Curaçao.67 Carmabins A 80 and B 81 are lipopeptides from L. majuscula that was also collected in Curaçao.68 An assemblage of L. majuscula and Schizothrix calcicola from Guam contained lyngbyastatin 1 82 which is an inseparable mixture of epimers at C-15 together with an inseparable mixture of dolastatin 12 83 which had previously been isolated from the sea hare Dolabella auricularia,69 and its 15-epi derivative.70 The cyanophyte Symploca hydniodes contained symplostatin 1 84 which is a homologue of the linear peptide dolastatin 10,71 that had been isolated previously from D.auricularia.72 Louludinium chloride 85 is a moderately cytotoxic pyridinium salt from a specimen of L. gracilis collected at Palmyra atoll lagoon.73 Phormidium ectocarpi which was isolated as an epiphyte of Udothea petiolata from Mallorca contained hierridin B 86 and the known metabolite 2,4-dimethoxy-6-heptadecylphenol.74 (2)-Malyngolide 87 which is an antimicrobial lactone from L. majuscula,75 has been 11 Nat. Prod. Rep. 2000 17 7–55 synthesized by four addtional routes that employ different strategies to accomplish the desired asymmetry.76–79 The epiphytic dinoflagellate Coolia monotis contained a new ceramide 88.80 The symbiotic dinoflagellate Symbiodinium sp.(strain no. Y-6) isolated from the flatworm Amphiscolops sp. produced the ceramide symbioramide-C16 89 the alkaloid zooxanthellamine 90 which closely resembles the alkaloid zoanthamine that was previously isolated from an Indian Zoanthus sp.,81 and zooxanthellabetaine A 91.82 Luteophanols B 92 and C 93 are additional polyols from an Amphidinium sp (strain no. Y-52) cultured from the Okinawan flatworm Pseudaphanostoma luteocoloris.83 Pectenotoxin-2 seco acid 94 and 7-epi-pectenotoxin-2 seco acid 95 are additional pectenotoxin derivatives that were produced by the dinoflagellate Dinophysis acuta and concentrated by the New Zealand greenshell mussel Perna canaliculus.84 The structure of (+)-amphidinolide A 96 which is a metabolite of the dinoflagellate Amphidinium sp.isolated from the flatworm Amphiscolops sp.,85 was confirmed by total synthesis.86 A stereocontrolled synthesis of hemibrevetoxin B 97 which is a metabolite of the cultured dinoflagellate Nat. Prod. Rep. 2000 17 7–55 12 Gymnodinium breve,87 was achieved in 56 steps and 0.75% overall yield from d-mannose.88 Bacillariolide II 98 which is an eicosanoid from the diatom Pseudonitzschia multiseries,89 has been synthesized from (R)-malic acid.90 Raikovenal 99 a bicyclic sesquiterpene isolated from the marine ciliate Euplotes raikovi,91 has been synthsized by a route that involves the formation of a bicyclo[3.2.0]heptenone intermediate as the first step.92 3 Green algae Among the polar metabolites of Caulerpa taxifolia from the Mediterranean were the glycoglycerolipid 100 and the stable enols 101 and 102 which occur in both (E) and (Z) forms.93 The structure of the cyano-sym-triazine halimedin 103 which was isolated from Halimeda xishaensis collected from the Xisha Islands in the South China Sea was determined by X-ray analysis.94 Although the sea grass Thalassia testudinum is certainly not a green alga its chemistry is probably best reported here.It has been demonstrated that the T. testudinum metabolite luteolin 7-O-b-d-glucopyranosyl-2B-sulfate 104 inhibits the growth of the co-occurring thaustrochytrid Schizochytrium aggregatum which is considered a fouling organism on T.testudinum.95 4 Brown algae An addiotional cis-dihydroxytetrahydrofuran (6S,7S,9S,10S)- 6,9-epoxynonadec-18-ene-7,10-diol 105 was described as part of a SAR study of the nematocidal properties of metabolites of Notheia anomala from southern Australia.96 A related metabolite of N. anomala (6S,7S,9R,10R)-6,9-epoxynonadec-18-ene- 7,10-diol 106,97 has been synthesized in an enantiocontrolled manner.98 Dictyopterene CA 107 which is a metabolite of Dictyopteris spp.,99 has been synthesized using a route that features asymmetric catalytic cyclopropenation.100 A series of endothelin antagonists the meroditerpenoids nahocols A 108 A1 109 B 110 C 111 D1 112 and D2 113 and isonahocols D1 114 and D2 115 were isolated from Sargassum autumnale from Japan.101 Two meronorsesquiterpenes cystomexicones A 116 and B 117 together with 4-(5-hydroxy- 2-methoxy-3-methylphenyl)-butan-2-one 118 were isolated from Cystoseira abies marina from Tenerife.102 Two diastereoisomeric meroditerpenes 119 and 120 and two new steroids (20S)-3b,20-dihydroxyergosta-5,24(28)-dien-16-one 121 and 3b-hydroxyergosta-5,24(28)-dien-16-one 122 were obtained from a South Australian specimen of Cystophora brownii.103 (+)-Zonarol 123 which is an antifungal sesquiterpene hydroquinone from Dictyopteris zonaroides,104 has been synthesized using an enantioselective enzymatic hydrolysis reaction to obtain chiral intermediates.105 Stypodiol 124 which is an ichthyotoxic agent from Stypopodium zonale,106 has been synthesized using an efficient stereoselective route from (+)-carvone.107 Two crenulide diterpenes 14-hydroxyacetoxycrenulide 125 and 13-hydroxyacetoxycrenulide 126 were isolated from a Dictyota sp.from Chile.108 Five linear diterpenes eleganolone 127 eleganolone acetate 128 elegandiol 129 eleganonal 130 and epoxyeleganolone 131 from Nat. Prod. Rep. 2000 17 7–55 13 Cystoseira balearica109,110 or Bifurcaria bifurcata111 have been synthesized from farnesol in high overall yields.112 5 Red algae Four methoxylated fatty acids 9-methoxypentadecenoic acid 132 9-methoxyheptadecenoic acid 133 13-methoxyheneicosa- Four sets of halogenated monoterpenes pantopyranoids A–C 144–146 pantoisofuranoids A–C 147–149 pantoneurotriols noic acid 134 and 15-methoxytricosanoic acid 135 were isolated as their methyl esters from a Sicilian specimen of Schizymenia dubyi after treatment with 3% hydrochloric acid in methanol but it is not clear whether the methoxylated fatty acids were present prior to methylation.113 Sulfoquinovosyldiacylglycerol KM043 136 is a potent inhibitor of eukaryotic DNA polymerases and HIV-1 reverse transcriptase type 1 from a Japanese specimen of Gigartina tenella.114 Among the constituents of a specimen of Gracilaria coronopifolia collected one week after an outbreak of G.coronopifolia food poisoning in Maui were two new malyngamides M 137 and N 138 together with malyngamide I acetate 139.115 The same group also isolated anhydrodebromoaplysiatoxin 140 and the known116 metabolite manauealide C from G.coronopifolia.117 The authors conclude that the specimen of G. coronopifolia was most likely contaminated with the cyanophyte Lyngbya majuscula and propose that malyngamide N 138 represents a revised structure for deacetoxystylocheilamide which had been isolated earlier from the sea hare Stylocheilus longicauda.118 The absolute configuration of constanolactone E 141 which is an eicosanoid from Constantinea simplex,119 has been determined by total synthesis.120 The structure and absolute configuration of polycavernoside A 142 which is a human toxin isolated from Polycavernosa tsudai,121 have been established by total synthesis.122 An efficient synthesis of trans-kumausyne 143 which is a metabolite of Laurencia nipponica,123 involved a tandem intramolecular alkoxycarbonylation-lactonization step.124 150 and 151 and the related isomeric linear monoterpenes 152 and 153 and pantoneurines A 154 and B 155 were all isolated from the Antarctic endemic Pantoneura plocamioides.125–127 Nat.Prod. Rep. 2000 17 7–55 14 The linear monoterpene 153 had previously been isolated from Plocamium cartilagineum.128 Plocamapyranoid 156 and a related pyran 157 were isolated from a Chilean specimen of P. cartilagineum.127 P. cartilagineum from Portugal contained 4-bromo-5-chloro-2-(E)-chlorovinyl-1,5-dimethyl-1,2-epoxycyclohexane 158 as a minor metabolite.129 The absolute configuration of (1S,2R,4R,5S,1AE)-2,4,5-trichloro-1-(2Achloroethynyl)-1,5-dimethylcyclohexane 159 from a Chilean specimen of P.cartilagineum130 was determined by X-ray crystallography.131 Halomon 160 which is an antitumor agent from Portieria hornemannii,132 has been synthesized as the racemate using a Johnson–Claisen rearrangement.133 The recently proposed structure of the Laurencia sp. metabolite cartilagineol 161,134 previously known as allo-isoobtusol,135 has been confirmed by X-ray crystallography and the NMR data of ma’ilione 162 has been reassigned.136 The brominated diterpene anhydroaplysiadiol 163 was isolated from L. japonensis a newly described species.137 As part of a study of abalone and sea urchin feeding deterrence three new diterpenes 164–166 were isolated from L.satoi together with fourteen known diterpenes all of which were assayed.138 Cholest-4-ene- 3a,6b-diol 167 was reported as a new sterol from Acantophora spicifera.139 Laurequinone 168 which is a metabolite of L. nidifica,140 has been synthesized using an intramolecular Heck reaction as a key step.141 A regiospecific bromination– cyclization reaction was applied to the synthesis of (±)-laurencial 169,142 which was obtained from L. nipponica.143 Filiforminol 170 from L. filiformis144 and the corresponding bromoether 171 from L. glandulifera145 and L. nana146 have been synthesized as racemates.147 Chondriamide C 172 is an additional indole alkaloid that was isolated together with 3-indoleacrylamide 173 from Chondria atropurpurea both displayed anthelmintic activity.148 The structure of martefragin A 174 which is an inhibitor of lipid peroxidation that was isolated from Martensia fragilis,149 was determined by X-ray crystallographic analysis and confirmed by synthesis.150 6 Sponges Although sponges remain the most prolific source of marine natural products the number of new metabolites has declined slightly in the past year.Several new fatty acids have been isolated from sponges including 2-methoxyhexadecanoic acid 175 from Amphimedon compressa,151 and both 11-methylpentadecanoic acid 176 and 10-tricosenoic acid 177 from Calyx podatypa.152 (5Z)-2-Methoxyhexadec-5-enoic acid 178 and (6Z)-2-methoxyhexadec-6-enoic acid 179 both of which were found in several Caribbean sponges,151,153 have been synthesized.154 The ceramide 180 which inhibits fouling by macroalgae was isolated from Haliclona koremella collected in Palau.155 The ceramides of four sponges from the Gulf of Mannar H. tenuiramosa Tedania annhelans Zygomycale parishii and Sigmadocia pumila have been briefly characterized. 156 Elenic acid 181 which is a topoisomerase II inhibitor from an Indonesian Plakinastrella sp.,157 has been synthesized from methyl (S)-3-hydroxy-2-methylpropionate.158 Five additional polyacetylenes petroformynic acid 182 isopetroformyne 1 183 23,24-dihydropetroformyne 4 184 20-oxoisopetroformyne 4 185 and 20-oxoisopetroformyne 3 186 were isolated from both Atlantic and Mediterranean specimens of Petrosia ficiformis.159 Two research groups have 15 Nat.Prod. Rep. 2000 17 7–55 reported that Korean specimens of Petrosia sp. contained petrocortynes A–H 187–194,160,161 petrosiacetylenes A 195 B 196 C 197 and D 198,160 and dideoxypetrosynols A 195 B 197 C 196 and D 199,162 representatives of which inhibit phospholipase A2 or show evidence of cytotoxicity. There appears to be some overlap in the metabolites reported such that petrosiacetylenes A B and C have been assigned the same structures as dideoxypetrosynols A C and B respectively although there still appears to be some confusion regarding the absolute configurations.160,162 Aztèquynols A 200 and B 201 are Cbranched acetylenes from a Petrosia sp. from New Caledonia. 163 A more complex series of highly oxygenated C47 polyacetylenes osirisynes A–F 202–207 were isolated as cytotoxins from a Korean specimen of Haliclona osiris.164 Callyspongynes A 208 and B 209 are two poorly characterized metabolites of a Callyspongia sp.from southern Australian.165 Two very unusual cytotoxic acetylenes 210 and 211 which also contain a cyclic peroxide ring were isolated from Acarnus cf. bergquistae from Eritrea.166 The total synthesis of (S,4E)-eicos- (4)-en-1-yn-3-ol 212 which is a cytotoxin isolated from Cribrochalina vasculum,167 employed an enzyme-catalysed reaction to prepare a key intermediate with high enantiomeric purity.168 A number of cyclic peroxides have been reported during the past year some of which appear to have been assigned the same Nat.Prod. Rep. 2000 17 7–55 16 structures with varying degrees of stereochemical detail. The reviewer has assumed that compounds with almost identical optical rotations and NMR data are identical and in these cases the more complete stereostructure has been reported. Six new cyclic peroxides 213–218 were isolated from an Okinawan Plakortis sp. and one of these the peroxide 213 was shown to be cytotoxic.169,170 The antileishmanial peroxides 219 and 220 were isolated from P. aff. angulospiculatus from Palau together with peroxide 221 and furans 222–224 which were inactive.171 Peroxides 213 and 221 have the same gross structure but the difference in optical rotations suggests that they have different stereochemistries. The furan 222 and peroxides 220 and 225–227 were obtained from a Plakortis sp.from the Amirantes Islands Seychelles.172 The close agreement of the optical rotations of 220 and 222 from the Palauan and Seychelles samples strongly suggests that they have the same stereochemistry. Three cytotoxic cyclic peroxides ethyl plakortide Z 228 ethyl didehydroplakortide Z 229 which demonstrated selective in vitro activity against solid tumors but lacked in vivo activity and methyl didehydroplakortide Z 230 and three related acyclic diols 231–233 were isolated from P. lita from Papua New Guinea.173 Three cyclic peroxides 234–236 and an undescribed carboxylic acid ester 237 were obtained from a Plakinastrella sp. from Hagakhak Island in the Philippines.174 Arenolide 238 is a moderately cytotoxic albeit unstable 14-membered macrolide that was isolated together with some dolabellane diterpenes from a Dysidea species from Palau.175 A Japanese specimen of Mycale sp.contained the minor metabolites thiomycalolides A 239 and B 240 which are highly cytotoxic glutathione adducts of the known metabolites mycalolides A and B.176 Three additional macrolides 30-hydroxymycalolide A 241 32-hydroxymycalolide A 242 and 38-hydroxymycalolide B 243 were isolated from M. magellanica from Japan.177 Three additional cytotoxins of the calyculin class clavosines A–C 244–246 were isolated as potent inhibitors of types 1 and 2A serine/threonine protein phosphatases from Myriastra clavosa from Chuuk Micronesia.178 Clavosine C 246 is considered to be an artifact derived from clavosine B 245.A new truncated calyculin derivative 247 from Theonella swinhoei was reported as a potent inhibitor of tumor cell proliferation but details of the structural elucidation were not disclosed.179 Two independent syntheses of the enantiomers of calyculin A 248 and calyculin B 249 and of the natural isomer of calyculin C 250 all of which are serine-threonine phosphatase inhibitors from Discodermia calyx,180,181 have been described.182,183 Complex macrolides and related metabolites from sponges continue to be favourite targets for synthesis. The synthesis of altohyrtin A (spongistatin 1) 251 which is a potent cytotoxic agent from sponges of the genus Hyrtios184 and Spongia,185 respectively provided an excellent example of the power of modern synthetic methodology.186The total synthesis of phorboxazole A 252 which is a potent but scarce antitumor agent from an Indian Ocean Phorbas sp.,187 employed a highly convergent strategy.188 The total synthesis of (2)-pateamine A 253 which a potent immunosuppressive agent from a New Zealand Mycale sp.,189 involved a b-lactam-based macrocyclization.190,191 Both mycalamide B 254 which is a potent antitumor agent from Mycale sp.,192 and theopederin D 255 a cytotoxin from a Theonella sp.,193 have been synthesized in an economical and efficient manner.194,195 Two total syntheses of (+)-callystatin A 256 which is a potent cytotoxin from the Japanese sponge Callyspongia truncata,196 follow somewhat similar strategies.197,198 An additional total synthesis of (+)-discodermolide 257 which is a potent cytotoxic and immunosuppressive agent from Discodermia dissoluta,199 has been reported.200 An efficent synthesis of the protein phosphatase inhibitor okadaic acid 258 which was first isolated from Halichondria okadai201 but has recently been found in Raspailia agminata and detected in Thorecta sp.and Chondropsis Nat. Prod. Rep. 2000 17 7–55 17 kirkii from New Zealand,202 was reported in detail,203 and a second convergent synthesis has been disclosed.204 An additional dibromotyramine derivative 259 was isolated from an Indian specimen of Psammaplysilla purpurea.205 5-Bromoverongamine 260 which inhibited the settling of barnacle larvae (EC50 1.03 mg mL21) was isolated from a Pseudoceratina sp.from Curaçao.206 Aiolochroia crassa from the Bahamas contained an additional bromotyrosine derivative N-methylaerophobin-2 261.207 Verongamine 262 which is a histamine-H3 antagonist from Verongia gigantea,208 hemibastadin-2 263 from Ianthella basta,209 and aerothionin 264 from Aplysina (Verongia) aerophoba210 have all been synthesized using the cyano ylide coupling strategy.211 Bastadins 2 265 3 266 and 6 267 which are metabolites of Ianthella basta,212 were synthesized using a chemoenzymatic oxidative coupling strat- Nat. Prod. Rep. 2000 17 7–55 18 egy.213 The antifouling agents ceratinamine 268 from Pseudoceratina purpurea214 and moloka’iamine 269 from a Hawaiian verongid sponge215 have also been synthesized.216 The (3R) absolute configuration of hiburipyranone 270 which is a cytotoxic metabolite of Mycale adhaerens,217 was established by total synthesis of both enantiomers.218 Phycopsisenone 271 which was isolated from an Indian Ocean Phycopsis sp.,219 has been synthesized in high yield.220 Twelve additional polychlorinated diketopiperazines dysamides I–T 272–283 were obtained from Dysidea chlorea from Yap Micronesia.221 Two further cyclodepsipeptides geodiamolides H 284 which was cytotoxic and I 285 the structure of which was determined by single crystal X-ray analysis were isolated from a Geodia sp.from Trinidad.222 Microciona eurypa from Palau contained the cyclic isodityrosine tripeptide eurypamide A 286 and an inseparable mixture of related tripeptides eurypamides B–D 287–289 that were identified but not characterized.223 Celenamide E 290 is an additional antimicrobial tripeptide alkaloid isolated from Cliona chilensis from Patagonia.224 The antiproliferative agents axinellins A 291 and B 292 are new proline-containing cyclic peptides from a specimen of Axinella carteri from Vanuatu that also contained five known cyclic peptides.225 Microsclerodermins C–E Nat.Prod. Rep. 2000 17 7–55 19 293–295 are antiifungal cyclic peptides that were isolated from specimens of Theonella sp. and Microscleroderma sp. from the same location in the Philippines.226 A Japanese Theonella sp. contained cyclotheonamides E2 296 and E3 297 which are potent serine protease inhibitors.227 Theopalauamide 298 is a bicyclic glycopeptide that was isolated from specimens of T.swinhoei from both Palau and Mozambique and from a filamentous bacterial symbiont found within the sponge.228 An Okinawan species of Theonella contained two new cytotoxic cyclic peptides keramamides K 299 and L 300 that both contain unusual tryptophan residues.229 An Indonesian specimen of T. swinhoei contained the antifungal cyclodepsipeptide cyclolithistide A 301.230 The structure of theonellapeptolide IIIe 302 which is a cytotoxic linear peptide from a deep-water sponge Lamellomorpha strongylata from New Zealand was confirmed by X-ray crystallography.231 The structure of axinastatin 4 303 which was isolated in very low yield as a cytotoxin from Axinella cf. carteri,232 has been confirmed by synthesis but the synthetic compound was devoid of cytostatic activity.233 Total Nat.Prod. Rep. 2000 17 7–55 20 synthesis of the (4R,7S,11R,14S)-isomer 304 of cyclocinamide A which is a cytotoxic hexapeptide from Psammocinia sp.,234 led to the suggestion that the natural product might possess the (4S,7S,11S,14S) absolute stereochemistrry.235 Arenastatin A 305 which is a cytotoxic depsipeptide from Dysidea arenaria, 236 has been synthesized in a concise manner.237 Sponges continue to produce unusual alkaloids an excellent example of which is halichlorine 306 which is a potent inhibitor of vascular cell adhesion molecule-1 (VCAM-1) that was obtained from Halichondria okadai from Japan. The absolute stereochemistry of halichlorine 306 was determined by degradation and synthesis of a degradation product.238 Axinellamines A 307 and B 308 are pyrrole alkaloids from an Axinella sp.from the Caribbean.239 Aaptos aaptos from Trinidad contained the new alkaloid aaptosamine 309 which appears to have incorporated a molecule of the extraction solvent acetone.240 As part of a paper that described their facile alumina-catalyzed isomerization the stereochemistry of araguspongines B 310 and E 311 which are metabolites of an Okinawan Xestospongia sp.,241 have been revised on the basis of NMR and X-ray crystallographic evidence.242 The absolute stereochemistries of (2)-araguspongine B 310 (+)-xestospongin A 312 (araguspongine D = 3:7 (+):(2) mixture) and xestospongin C 311 (araguspongine E) were corrected on the basis of their biomimetic synthesis.243 Petrosin 313 and petrosins A–D 314–317 which are metabolites of Petrosia seriata,244–246 have all been synthesized.247,248 Although dilemmaones A–C 318–320 were originally obtained from a mixed collection of three South African sponges a process of elimination suggested that the most likely source was Ectyonanchora flabellata.249 Iso-trans-trikentrin B 321 which was isolated from Trikentrion flabelliforme,250 has been synthesized as its racemate.251 Four additional imidazole alkaloids isonaamine B 322 isonaamidine D 323 bis(isonaamidinato B)zinc(ii) 324 and (isonaamidinato B)(isonaamidinato D)zinc(ii) 325 were obtained from a specimen of the calcareous 21 Nat. Prod. Rep. 2000 17 7–55 sponge Leucetta cf.chagosensis from Yap Micronesia.252 Dragmacidin E 326 and the known analogue dragmacidin D were isolated as serine-threonine protein phosphatase inhibitors from an Australian deep-water sponge of the genus Spongosorites. 253 The total synthesis of topsentin 327 which is an antiviral and cytotoxic agent from Topsentia genitrix254 and Spongosorites sp.,255 employed regioselective substitution of the imidazole ring.256 As part of a paper that reported the insecticidal activity and cytotoxicity of kuanoniamines C 328 and D 329 an additional pyridoacridine alkaloid N-deacetylkuanoniamine C Nat. Prod. Rep. 2000 17 7–55 22 330 was reported from an Oceanapia sp. from Truk Micronesia. 257 Renieramycins H 331 and I 332 are two antimicrobial alkaloids from Haliclona cribricutis from India.258 The pyrroloiminoquinone alkaloids makaluvamines A 333 C 334 D 335 I 336 and K 337 from Zyzzya spp.259,260 and the methylthio derivative isobatzelline B 338 from a Batzella sp.261 have all been synthesized.262–264 The stereochemistry of the side chain double bond of batzelladine E 339 which is an alkaloid from a Caribbean Batzella sp.,265 was revised from E to Z as the result of a very efficient total synthesis.266 Haliclorensin 340 is a medium ring alkaloid from Haliclona tulearensis from South Africa.267 Xestospongia exigua from Papua New Guinea contained three cytotoxic medium-ring alkaloids motuporamines A–C 341–343.268 Madangamines B– E 344–347 are additional pentacyclic alkaloids from X.ingens from Papua New Guinea.269 Two additional alkaloids haliclonacyclamines C 348 and D 349 were obtained from a Haliclona sp.from the Great Barrier Reef.270 The structure of haliclonacyclamine B 350 was revised on the basis of an X-ray crystallographic study and the NMR spectral data of haliclonacyclamines A 351 and B 350 were reassigned.270 Three additional manzamine congeners manzamine M 352 3,4-dihydromanzamine J 353 and 3,4-dihydro-6-hydroxymanzamine A 354 were isolated from a Japanese Amphimedon sp.271 Ma’eganedin A 355 obtained from a Japanese Amphimedon sp. is a very unusual manzamine alkaloid that contains an additional ring formed by addition of a methylene bridge between two nitrogen atoms.272 The absolute configurations of isosaraine-1 356 and isosaraine-2 357 which are metabolites of Reniera sarai from Naples,273 have been determined by application of Mosher’s method.274 A different species of Reniera from Naples contained the unusual zwitterionic alkaloid misenine 358 the structure of which was selected from three possible isomers on the basis of its proposed biosynthesis.275 The first total syntheses of ircinol A 359 ircinal A 360 and manzamines A 361 and D 362 which are alkaloids from Okinawan Haliclona,276 Amphimedon277 and Ircinia species,278 employed a common synthetic pathway.279 The cyclic bis-pyridinium salts cyclostellettamines A–F 363–368 which are inhibitors of the binding of methyl quinuclidinyl benzylate to muscarinic acetyl choline receptors from Stelletta maxima (probably contaminated with a Haliclona sp.),280 were synthesized using high dilution conditions for the cyclization step.281 A second synthesis of the cyclostellettamines 363–368 confirmed the dimeric nature of the synthetic products by measuring the exact masses of the bis-tetrahydropyridine derivatives.282 The total syntheses of the cyclic bis-tetrahydropyridine alkaloids halicyclamines A 369 and B 370 which were isolated from a Haliclona sp.,283 have also been reported.284 In testing the proposed biosynthetic pathway to the 23 Nat.Prod. Rep. 2000 17 7–55 manzamine alkaloids,285 the cyclic bis-pyridinium salt 371 was converted into keramaphidin B 372 albeit in very low yield.286 The structure of 2-cyano-4,5-dibromopyrrole 373 from Agelas oroides287 was confirmed by a single crystal X-ray analysis.288 Two additional bromopyrroles 5-bromopyrrole- Nat.Prod. Rep. 2000 17 7–55 24 2-carboxamide 374 and 5-bromopyrrole-2-(N-methoxymethyl) carboxamide 375 were obtained from A. nakamurai from Papua New Guinea.289 4,5-dibromopyrrole-2-(N-methoxymethyl) carboxamide 376 and the racemic methyl ester 377 of hanishin290 were isolated from a deep-water Homoaxinella sp. from Japan.291 The corresponding carboxylic acid longamide 378 and the isomeric clathramides C 379 and D 380 were reported from a Caribbean specimen of A. dispar.292 An unusual bromopyrrole 381 was obtained from Axinella carteri from Chuuk Micronesia.293 Spongiacidins A–D 382–385 two of which 382 and 383 inhibited c-erbB-2 kinase and cyclindependent kinase 4 are minor constiuents of a Hymeniacidon sp.from Okinawa.294 Debromosceptrin 386 was obtained as a minor constituent of Agelas dispar from Belize.295 In a paper that reported the insecticidal activity of agelastatin A 387,296 two additional agelastatins C 388 and D 389 were described as metabolites of a Cymbastela sp. from Western Australia.297 4-Bromopalau’amine 390 and 4,5-dibromopalau’amine 391 25 Nat. Prod. Rep. 2000 17 7–55 were isolated together with four previously reported metabolites as minor metabolites of the Palauan sponge Stylotella aurantium which was incorrectly identified in an earlier paper298 as S. agminata.299 The Chinese sponge Phacellis fusca yielded fuscain 392 which is a furanolactam related to the Nat.Prod. Rep. 2000 17 7–55 26 pyrrololactam aldisin 393 but only after treatment of a yellow oil with methanol–chloroform to obtain the crystalline metabolite. 300 Keramidine 394 which is an antagonist of serotonergic receptors of the rabbit aorta from an Agelas sp.,301 has been synthesized using reduction of an alkyne to form the (Z) olefin.302 Synthetic and antifouling studies of pseudoceratidine 395 which was isolated from Pseudoceratina crassa,303 have been reported.304 Oroidin 396 from Agelas oroides,305 clathrodin 397 from A. clathrodes,306 and dispacamide 398 and monobromodispacamide 399 from Agelas spp.307 have all been synthesized in a very efficient manner.308 Although reported as an unprecedented compound from Agelas oroides the pyridone 400 which was isolated along with the known piperidone 401 is probably an artifact resulting from using acetone as a solvent for chromatography of alkaloids.309 The unusual cyclic lysine derivative 402 was found in Axinyssa terpnis from Chuuk Micronesia.293 An Australian Dendrilla sp.contained a new amino acid cis- 3-hydroxy-N-methyl-l-proline 403.310 The guanidine alkaloids 7,8-dihydrotubastrine 404 and 4-deoxy-7,8-dihydrotubastrine 405 were obtained from Petrosia cf. contignata from Papua New Gunea.311 Agelas dispar from the Bahamas contained three betaine alkaloids aminozooanemonin 406 pyridinebetaine A 407 and pyridinebetaine B 408 of which 406 and 407 showed moderate antibacterial activity.312 1-Carboxymethylnicotinic acid 409 was isolated from Anthosigmella cf.raromicrasclera from Japan as a cystein protease inhibitor and its structure was confirmed by synthesis.313 The alkaloid erinacean 410 was obtained from the Antarctic sponge Isodictya erinacea. 314 Girolline 411 which is a potent cytotoxic agent from Cymbastela cantharella (previously Pseudaxinyssa cantharella) that recently failed in phase 1 clinical trials due to unfavourable side effects,315 has been synthesized as the racemate by a two step process.316 Bolinaquinone 412 is a cytotoxic sesquiterpene quinone from a Philippine Dysidea sp. that acts by interfering with or damaging DNA.317 The structure of 4A-methylaminoavarone 413 which is a minor constituent of D. avara,318 was confirmed by X-ray crystallography.319 A Euryspongia sp.from Chuuk Micronesia contained the sesquiterpene hydroquinone derivatives frondosins A 414 and D 415 which inhibited HIV-1 in the NCI primary screen.320 Wiedenols-A 416 and -B 417 which are cholesteryl ester transport protein inhibitors from Xestospongia wiedenmayeri,321 have been synthesized from (2)-sclareol or 27 Nat. Prod. Rep. 2000 17 7–55 (+)-cis-abienol.322 Arenarol 418 which is a cytotoxic metabolite of D. arenaria,323 has been synthesized as the racemate,324 and ilimaquinone 419 from Hippospongia metachromia325 has again been synthesized using an established strategy.326 An Indonesian Xestospongia sp. yielded three additional halenaquinone derivatives 15-methoxyhalenaquinone 420 11,18-dimethyl-9-hydroxyhalenaquinone 421 and noelaquinone 422 which contains a triazine ring.327 (+)-Xestoquinone 423 halenaquinone 424 and halenaquinol 425 which are metabolites of X.sapra and X. exigua,3282330 have been synthesized using an asymmetric Heck reaction as the key step.331,332 The meroditerpene dimer distrongylophorine 426 which was obtained from an undescribed Strongylophora sp. from the Philippines was active in the brine shrimp lethality assay.333 Adociasulfate-2 427 is a metabolite of the Palauan sponge Haliclona (aka Adocia) sp. that inhibited activity of the motor protein kinesin by interfering with the binding of kinesin to microtubules.334 A Dysidea sp. from the Great Barrier Reef contained two cytotoxic sesquiterpenes D7,14-isonakafuran-9 428 and the related hydroperoxide 429 the structure of which was determined by single crystal X-ray analysis.335 A specimen of D.fragilis from the Indian Ocean contained the oxygenated furanosesquiterpene 430.336 Three sesquiterpene carbonimidic Nat. Prod. Rep. 2000 17 7–55 28 dichlorides 431–433 from an Axinyssa sp. and a sesquiterpene peroxide 434 from a second Axinyssa sp. showed potent antifouling activity against larvae of the barnacle Balanus amphitrite.337 The structures of 4a-formamidogorgon-11-ene 435 and 4a-isocyanogorgon-11-ene 436 were confirmed by mchloroperbenzoic acid oxidation to the unusual cyclized derivatives 437 the structure of which was determined by X-ray analysis and 438 respectively.338 The structure of (+)-12ahydroxyisodrimenin 439 which was isolated from Dysidea fusca,339 has been confirmed by total synthesis.340 (+)-Curcuphenol 440 which is a gastric H K-ATPase inhibitor from Didiscus flavus,341 has been synthesized by two stereocontrolled routes.342,343 Pallescensin A 441 a metabolite of Dysidea pallescens,344 has been synthesized as its racemate.345 A Raspailia sp. from New Zealand contained two clerodane diterpenes raspailenone 442 and raspailol 443.346 Three dolabellane diterpenes (1R*,2E,4R*,7E,10S*,11S* 12R*)-10,18-diacetoxydolabella-2,7-dien-6-one 444 (1R* 2E,4R*,7Z,10S*,11S*,12R*)-10,18-diacetoxydolabella- 2,7-dien-6-one 445 and (1R*,2E,4R*,8Z,10S*,11S*,12R*)- 10,18-diacetoxydolabella-2,8-dien-6-one 446 were obtained from a Dysidea species from Palau.175 Two additional spongian diterpenes 447 and 448 together with four known analogues were isolated from Spongia matamata from Yap.347 Spongian- 16-one 449 which was obtained from Dictyodendrilla cavernosa348 and Chelonaplysilla violacea,349 has been synthesized as the racemate using a cascade of radical cyclizations to form the ring system.350 Another metabolite of a Dictyodendrilla sp.dictyodendrillin-B 450,351 was prepared by a concise route in 43% overall yield.352 Five new diterpenes polasols A– C 451–453 peroxypolasol 454 and mugipolasol 455 were isolated from a Japanese species of Epipolasis.353,354 Seven minor diterpene isonitriles and isothiocyanates D9-kalihinol Y 456 kalihinols K 457 and L 458 10-isothiocyanatokalihinol G 459 10-epi-kalihinol H 460 10-isothiocyanatokalihinol C 461 and pulcherrimol 462 were isolated from a specimen of Phakellia pulcherrima from the Philippines.355 As part of a study that demonstrated the antimalarial activity of kalihinol A three additional diterpene isonitriles and isothiocyanates D9- kalihinol Y 456 10-epi-kalihinol I 463 and 5,10-bisisothiocyanatokalihinol G 464 were obtained from an Acanthella sp.from Okinawa.356 Agelasines H 465 and I 466 are two new antimicrobial 9-methyladeninium substituted diterpenes from an Agelas sp. from Yap Micronesia.357 An additional diterpene 9-methyladeninium alkaloid 467 was isolated from A. nakamurai from Papua New Guinea.289 Three unusual diterpene 9-methyladeninium alkaloids asmarines A–C 468–470 were isolated as cytotoxic constituents of a Raspailia sp.from Eritrea and the structure of asmarine A 468 was determined by single crystal X-ray analysis.358 Specimens of Diacarnus cf. spinopoculum from the Solomon Islands and Papua New Guinea yielded ent-muqubilin A 471 ent-epimuqubilin A 472 nuapapuin B 473 epinuapapuin B 474 muqubilin B 475 epimuqubilin B 476 and muquketone 477 together with known metabolites all of which were evaluated 29 Nat. Prod. Rep. 2000 17 7–55 for cytotoxicity.359 Esterification of carboxylic acid mixtures from the New Caledonian sponge D. levii resulted in the isolation of the benzyl esters of ent-muqubilin A 471 and deoxydiacarnoate B 478 and the methyl ester of diacarnoate B 479 which together with known peroxides were screened for antimalarial activity.360 Two different species of Mycale from the Great Australian Bight and New South Wales contained mycaperoxide G methyl ester 480 which was obtained after treatment of the crude extract with diazomethane and the norterpene ketone 481 related to the known norsesterterpene mycaperoxide G methyl ester respectively.361 Trunculins G–I 482–484 are additional norsesterterpene cyclic peroxides again isolated after methylation of the crude extract from an Nat.Prod. Rep. 2000 17 7–55 30 Australian Latrunculia sp.362 Two additional norsesterterpenes rhopaloic acids B 485 and C 486 were isolated as potent inhibitors of gastrulation in starfish (Asterina pectinifera) embryos from a Japanese species of Rhopaloeides.363 The absolute stereochemistry of the cytotoxin rhopaloic acid A 487 from Rhopaloeides sp.364 has been determined by total synthesis of both enantiomers.365 Bioassay-guided isolation of serine protease inhibitors from Coscinoderma mathewsi yielded the 1-methylherbipoline salts 488 and 489 of the known sesterterpenes halisulfate-1366 and suvanine,367 both of which are incorrectly represented in this paper.368 Lintenolides F 490 and G 491 are two additional antiproliferative sesterterpenes from the Caribbean sponge Cacospongia cf.linteiformis.369 Cacospongionolide E 492 is an inhibitor of human secretory phospholipase A2 that was isolated as a minor constituent of Fasciospongia cavernosa from the Adriatic Sea.370 Five potent and selective phospholipase A2 inhibitors petrosaspongiolides M 493 N 494 P 495 Q 496 and R 497 were obtained from Petrosaspongia nigra from New Caledonia.371 A Cacospongia sp.from New Zealand contained 12-desacetylfuroscalar-16-one 498.372 An unusual 23,24-bishomoscalarane sesterterpene 499 was isolated from a specimen of C. scalaris from the Northern Adriatic.373 Four additional cytotoxic scalarane sesterterpenes 500–503 were obtained from a Japanese specimen of Hyrtios erecta the structure of sesterterpene 500 was determined by X-ray crystallography.374 A specimen of H. erecta from the Maldives contained the cytotoxic sesterterpenes sesterstatins 1–5 504–508 the structures of sesterstatins 4 507 and 5 508 were determined by X-ray analysis.375,376 Spongia agaricina from Cádiz Spain contained the sesterterpenes 12,16-di-epi-12-O-deacetyl-16-Oacetylfuroscalarol 509 and 16-epi-scalarolbutenolide 510 together with the cytotoxic 9,11-secosterols 3-O-deacetylluffasterol B 511 and 3-O-deacetyl-22,23-dihydro-24,28- dehydoluffasterol B 512.377 A specimen of Phyllospongia foliascens from the South China Sea contained phyllofolactones F 513 and G 514 and phyllactones D 515 and E 516.378 Two additional syntheses of (+)-dysidiolide 517 which is a cdc25A protein phosphatase inhibitor from Dysidea etherea,379 have been reported.3802382 Both the (8S,21S,22S,23R) and (8R,21S,22S,23R) isomers of okinonellin B 518 which is a cytotoxic and antispasmodic agent from Spongionella sp.,383 have been synthesized but neither has the same optical rotation as the natural product.384 The cyclization of ircianin 519 which is a metabolite of Ircinia wistaria,385 to form wistarin 520 which was obtained from the same sponge,386,387 has been 31 Nat.Prod. Rep. 2000 17 7–55 accomplished in 35% yield.388 Manoalide 521 which is an irreversible inhibitor of phospholipase A2 from Luffariella variabilis,389 has been synthesized by a route that employed a hetero Diels–Alder cyclization to form the dihydropyran ring.390 Agosterol A 522 is a polyhydroxylated sterol acetate from a Japanese Spongia sp. that completely reverses multidrug resistance in carcinoma cells caused by overexpression of two membrane glycoproteins.391 Two interesting steroidal akaloids 523 and 524 which contain an expanded B-ring were isolated Nat.Prod. Rep. 2000 17 7–55 32 from a Pacific species of Corticium.392 An Acanthodendrilla sp. from Japan contained ten steroidal sulfates acanthosterol sulfates A–J 525–534 two of which acanthosterol sulfates I 533 and J 534 showed antifungal activity against Saccharomyces cervisiae A364A and its mutants at 0.1 mg per disk.393 Crellastatin A 535 is the first of a series of cytotoxic bissteroidal sulfates from a Crella sp. from Vanuatu.394 A nortriterpenoid 536 was isolated from the deep-sea sponge Sarcotragus spinulosus from the Tasman Sea.395 The structure of hippospongic acid A which was isolated as an inhibitor of gastrulation of starfish embryos from a Japanese Hippospongia sp.,396 was revised from 537 to 538.397 The previously reported structure of hippospongic acid A 537 was also synthesized.398 The structures of yardenone 539 and abudinol 540 which are additional triterpenes from an Eritrean specimen of Ptilocaulis spiculifera were determined by X-ray crystallography.399 7 Coelenterates In the past year the vast majority of metabolites reported from coelenterates were terpenes or steroids.There is only one new lipid to report namely microspicamide 541 from the soft coral Lobophytum microspiculatum from Nansha Island China.400 The only other paper in this area concerned chlorovulone II 542 a marine prostanoid from Clavularia viridis,401 which was synthesized as its racemate.402 An Okinawan specimen of C. viridis contained the pyrazine derivative clavulazine 543 the structure of which was determined by X-ray crystallography.403 In a “headline article” on structure–activity relationships of compounds in the norzoanthamine 544 series that exhibit significant inhibition of osteoporosis several new natural products oxyzoanthamine 545 norzoanthaminone 546 cyclozoanthamine 547 and norzoanthamine 548 were reported from a Japanese Zoanthus sp.without supporting data.404 A specimen of Zoanthus sp. from Tenerife contained an additional alkaloid epioxyzoanthamine 549.405 An improved synthesis of coelentarazine 550 which is the preluciferin from the liver of the squid Watasenia scintillans,406 has been reported.407 Six additional guaiane lactones 10-epimethoxyamericanolide A 551 10-epiamericanolide C 552 8-epimethoxyamericanolide A 553 8-epiamericanolide C 554 methoxyamericanolide H 555 and methoxyamericanolide I 556 were isolated from a Puerto Rican specimen of Pseudopterogorgia americana.408 The structure and stereochemistry of 10-epimethoxyamericanolide A 551 were confirmed by single crystal X-ray analysis408 as were the structure and stereochemistry of 33 Nat. Prod. Rep. 2000 17 7–55 methoxyamericanolide B 557.409 Bebryazulene 558 is a guaiane furan from the gorgonian Bebryce grandicalyx collected in the Comoros Islands.410 The Brazilian gorgonian Phyllogorgia dilatata contained (E)-germacra-1(10),4(15),7(11)-trien-5-ol- 8-one 559 together with known compounds.411 Two additional sesquiterpenes capnellen-8b-ol 560 and 3b-acetoxycapnellene- 8b,10a,14-triol 561 which is somewhat confusingly given an incorrect name in the body of the paper were isolated from an Indonesian specimen of Capnella imbricata and assayed for cytotoxicity.412 D9(12)-Capnellene 562 which is the simplest metabolite of C.imbricata,413 has been synthesized as the racemate from p-cresol.414 Precapnelladiene 563 from C. imbricata,415 has been synthesized as the racemate using a strategy involving an oxy-Cope rearrangement.416 Four new subergorgic acid analogues 564–567 were obtained from Subergorgia suberosa from the Indian Ocean.417 Germacrene E 568 was isolated from a specimen of the soft coral Sinularia erecta from the Comoros Islands.418 Curcumene 569 which is Nat. Prod. Rep. 2000 17 7–55 34 a metabolite of Pseudopterogorgia rigida,419 has been synthesized by an enantioselective route.343 Cembranoids and their cyclized derivatives continue to be the most abundant metabolites of soft corals and gorgonians.Three new cembranoids sarcphytol T 570 (1E,3E,7E,11R*,12R*)- 15-(acetoxymethyl)cembra-11,12-epoxy-1,3,7-triene 571 and [1E,3R*,4R*,7E,11R*,12R* or (11S*,12S*)]-15-(acetoxymethyl) cembra-3,4:11,12-diepoxy-1,7-triene 572 were isolated from the soft coral Sarcophyton ehrenbergi from the Great Barrier Reef.420 A specimen of the soft coral Lobophytum catalai from the Andaman and Nicobar Islands contained (1E,3E,7E)-cembra-11,12-dihydroxy-1,3,7-triene 573 and (1S,3E,11E)-cembra-8,13,16-trihydroxy-3,11-diene 574.421 Sinuflexolide 575 dihydrosinuflexolide 576 and sinuflexibilin 577 were obtained from a Taiwanese specimen of the soft coral Sinularia flexibilis.422 Seven minor cembranoids 12,13-bisepieupalmerin epoxide 578 12,13-bisepieuprolide B 579 12,13-bisepieuprolide B acetate 580 uproeunicin 581, 12,13-bisepieuprolide D acetate 582 eunicenolide 583 and uproeuniolide 584 were isolated from the gorgonian Eunicea succinea from Mona Island Puerto Rico.423 Sinuflexin 585 is a cytotoxic biscembranoid from a specimen of the soft coral Sinularia flexibilis from Formosa.424 13-Hydroxyneocembrene 586 which was isolated from the soft coral Sarcophyton trocheliophorum,425 has been synthesized as a racemate.426 A new cembranoid 587 and two relatively unstable eudesmane-based diterpenoids 588 and 589 were isolated from a specimen of Lobophytum crassum from the Great Barrier Reef.427 L.pauciflorum from the Philippines contained four additional lobane diterpenes 14,17-epoxyloba-8,10,13(15)- trien-18-ol 18-acetate 590 loba-8,10,13(15)-triene-17,18-diol 18-acetate 591 18-methoxyloba-8,10,13(15),16(17)-tetraene 592 and 14,18-epoxyloba-8,10,13(15)-trien-17-ol 593.428 (+)-Fuscol 594 which was isolated from the gorgonian Eunicea fusca,429 has been synthesized in an enantioselective manner in quite high yield.430 Two additional diterpene glycosides lemnaboursides B 595 and C 596 were obtained from the soft coral Lemnalia bournei from the South China Sea.431 Seven additional diterpenes florlides A–E 597–601 and florethers A 602 and B 603 were isolated from a Japanese sample of Xenia florida.432 Alcyonide 5 604 has been obtained from two unidentified alcyonaceans from the Great Barrier Reef.433 The structures of pinnatins A–E 605–609 which are cyclopropane-containing diterpenes from the Caribbean gorgonian Pseudopterogorgia bipinnata were all determined by single crystal X-ray diffraction analyses.434 Photolysis of bipinnatin J 610 which is a newly-described metabolite of P.bipinnata gave kallolide A 611 as the major product,435 together with minor amounts of pinnatins A 605 and C 607 the formation of which requires an unexpected epimerization at C- 2.434 The stereoselective total synthesis of kallolide A 611 which is an antiinflammatory agent from Pseudopterogorgia kallos,436 employs an interesting allenoic acid cyclization.437 Two additional minor diterpenes the bis-epoxide 612 and the norcembranoid gorgiacerolide 613 were obtained from a Puerto Rican specimen of P.acerosa.438 The structures of sarcophytin 614 a metabolite of the soft coral Sarcophyton elegans and havellockate 615 which was isolated from Sinularia granosa both of which organisms were collected from the Andaman and Nicobar Islands were determined by X-ray analyses.439,440 The same specimen of S. elegans also contained D7(15)-dehydrosarcophytin 616.441 A specimen of S. dissecta from southern India contained rameswarolide 617.442 Chatancin 618 which is an antagonist of platelet activating factor from Sarcophyton sp.,443 has been synthesized as its racemate.444 Elisabethins A– C 619–621 one of which 620 showed significant antitumor activity and elisabanolide 622 were isolated from a Columbian sample of the gorgonian Pseudopterogorgia elisabethae.445 35 Nat.Prod. Rep. 2000 17 7–55 Diterpenes from coelenterates are frequently the targets of total synthesis. Both palominol 623 from the gorgonian Eunicea laciniata446 and dolabellatrienone 624 from E. caliculata447 have been synthesized by a concise route involving an oxy- Cope rearrangement.448 Claenone 625 which is a cytotoxin from an Okinawan Clavularia sp.,449 was synthesized from dmannitol. 450 The stereochemistry of helioporin D 626 which is a cytotoxic metabolite of Heliopora coerulea,451 has been revised as the result of total synthesis of the incorrect structure followed by synthesis from seco-pseudopterosin aglycone.452,453 The total syntheses of eleutherobin 627 which is a potent cytotoxin from a Western Australian Eleutherobia sp.,454 eleuthosides A 628 and B 629 which were obtained from E. aurea from South Africa,455 and sarcodictyins A 630 and B 631 from the Mediterranean stoloniferan coral Sarcodictyon roseum456 have been reported in a series of papers.4572461 In addition to several known briarane diterpenoids an Indonesian Briareum sp. contained 2,9-diacetyl-2-debutyrylstecholide H 632 13-dehydroxystecholide J 633 and 2bacetoxy-2-(debutyryloxy)stecholide E acetate 634 which had previously been reported as a semisynthetic metabolite.462 Two new ichthyotoxic briarane derivatives 635 and 636 were isolated from a Briareum sp.from Japan.463 Excavatolides A–E 637–641 are new cytotoxic briaranes from the Formosan gorgonian Briareum excavatum the stereostructure of excavatolide B 638 was confirmed by X-ray analysis.464 The Indian Ocean gorgonian Gorgonella umbraculum contained one new briarane diterpene 642 in addition to known analogues. 465 Erythopodium caribaeorum from Tobago contained an additional diterpene erythrolide K 643 which was linked to erythrolide B 644466 by a series of interconversions.467 The Mediterranean colonial anthozoan Cladocora cespitosa contained two sesterterpenes cladocorans A 645 and B 646 that are more typical of compounds produced by sponges.468 Nat. Prod. Rep. 2000 17 7–55 36 Six minor cytotoxic sterols 647–652 were isolated from an Arctic Ocean sample of the soft coral Gersemia fruticosa.469 Two additional cytotoxic sterols 24-methylcholesta- 5,24(28)-diene-3b,15b,19-triol 653 and 24-methylcholesta- 5,24(28)-diene-3b,19-diol-7-one 654 were obtained together with known cytotoxic sterols from the soft coral Nephthea erecta.470 A Brazilian specimen of the gorgonian Lophogorgia punicea contained punicin 655 which is an unusual 17-hydroxy sterol.471 Calicoferols F–I 656–659 are additional cytotoxic and PLA2 inhibitory 9,10-secosterols from a Korean Muricella species.472 Calicoferol E 660 from a Calicogorgia sp.473 and astrogorgiadiol 661 from an Astrogorgia sp.474 have both been synthesized from vitamin D3.475 Two polyhydroxylated dinostane sterols 662 and 663 were obtained from Pseudopterogorgia americana from Puerto Rico.476 An Indonesian Lophogorgia species contained 3b,7b,11-trihydroxy-5a,6a-epoxy-9,11-secogorgostan-9-one 664.477 3b,6a,11-Trihydroxy-9,11-seco- 5a-cholest-7-ene-9-one 665 and both 24S- and 24R-methyl- 3b,6a,11-trihydroxy-9,11-seco-5a-cholest-7,22E-diene-9-ones 37 Nat.Prod. Rep. 2000 17 7–55 666 and 667 were isolated from the gorgonian Subergorgia suberosa from the Indian Ocean.478 8 Bryozoans Among the few new bryozoan metabolites reported during 1998 were euthyroideones A–C 668–670 which were isolated from Euthyroides episcopalis from New Zealand.479 The structure of euthyroideone A 668 was determined by an X-ray crystallographic study. An additional antineoplastic agent bryostatin 19 671 was obtained from a specimen of Bugula neritina from the South China Sea.480 Bryostatin 2 672 which is an important anticancer agent from Bugula neritina,481 has been synthesized in a convergent manner.482 Although total synthesis of the natural bryostatins in commercial quantities remains an elusive goal efforts to find simpler analogues that retain activity have been quite successful.483,484 9 Molluscs Studies of the Indo-Pacific sea hare Dolabella auricularia continue to yield cytotoxic metabolites such as aurilol 673 a triterpene that was isolated from a Japanese specimen and that is related to metabolites of red algae of the genus Laurencia.485 Dolastatin 17 674 is a cytotoxic cyclic depsipeptide that was isolated from a Papua New Guinea specimen of D.auricularia. 486 Aplysia dactylomela from Brazil contained dehydroxyprepacifenol epoxide 675 which was subjected to detailed NMR analysis.487 Aplysiapyranoid C 676 which is a cytotoxic agent isolated from A. kurodai,488 was synthesized in good overall yield.489 Nat. Prod. Rep. 2000 17 7–55 38 Limaciamine 677 is a diacylguanidine that was isolated from the skin of the North Sea nudibranch Limacia clavigera.490 The cephalaspidean Haminoea callidegenita from the Mediterranean contained a series of alkyl phenols 678–682 that were located exclusively in the parapodia.491 Haminols A 683 B 684 and C 685 and navenones A 686 and B 687 which are alarm pheromones from H. navicula492,493 and Navanax inermis,494 respectively have been synthesized using an enatioselective approach that employs the Suzuki reaction as a key step.495,496 The stereochemistry of ulapualide A 688 which is a macrocyclic metabolite of the nudibranch Hexabranchus sanguineus, 497 has been established by total synthesis as that predicted498 from a molecular mechanics study of postulated metal chelate.499 (+)-Pectinatone 689 which is a metabolite of Siphonaria pectinata,500 was synthesized using an iterative process to establish the stereochemistry of the side chain.501 The mid-intestinal gland of the Japanese muricid gastropod Drupella fragum which feed upon the tissues of Madreporaria corals contained the brominated indoles 690–692 and the antimicrobial indolequinones 693–695.502,503 An additional group of cytotoxic cyclic depsipeptides kulolides-2 696 and -3 697 the kulokainalide-1 698 and kulomo’opunalides -1 699 and -2 700 together with tolytoxin-23-acetate 701 were isolated from the Hawaiian cephalaspidean Philinopsis speciosa.504 Hodgsonal 702 is a drimane sesquiterpene from the mantle of the Antarctic nudibranch Bathydoris hodgsoni.505 The sesquiterpene isonitrile 703 was isolated as an antifouling agent from the Japanese nudibranch Phyllidia pustulosa.337 An additional labdane diterpene 2a,6b,7a-triacetoxylabda-8,13-dien-15-ol 704 was isolated together with a known diterpene from the South African pulmonate Trimusculus costatus.506 The unusual 39 Nat. Prod. Rep. 2000 17 7–55 seco-spongiane diterpene tyrinnal 705 was isolated together with several known sesquiterpenes from the Patagonian nudibranch Tyrinna nobilis.507 An additional sesterterpene 22-deoxy-23-hydroxymethylvariabilin 706 was isolated together with several known sesquiterpenes and sesterterpenes from both the South African nudibranch Hypselodoris capensis and the sponge Fasciospongia sp.on which it was feeding.508 Albicanol 707 which is a metabolite of Cadlina luteomarginata, 509 was synthesized in an efficient manner.510 Tochuinyl acetate 708 and dihydrotochuinyl acetate 709 which were isolated from the skin extracts of the North Pacific dendronotid nudibranch Tochuina tetraquetra,511 have been synthesized as their racemates.512 Nat. Prod. Rep. 2000 17 7–55 40 Azaspiracid 710 is a new type of diarrhetic shellfish toxin that was isolated using a mouse toxicity assay from the mussel Mytilus edulis cultivated in Ireland.513 Pectenotoxins (PTX) 4 711 and 7 712 which were isolated from the Japanese scallop Patinopecten yessoensis were identified as the 7-epi isomers of PTX1 and PTX6 respectively.514 The structure of pinnatoxin A 713 which is a toxin from Pinna muricata,515 has been confirmed and its absolute stereochemistry determined by total synthesis of its antipode.516 Adriatoxin 714 is an additional yessotoxin analogue that was isolated from the digestive glands of the mussel Mytilus galloprovincialis from the Adriatic coast of Italy.517 An additional brevetoxin analogue brevetoxin B2 (BTXB2) 715 was isolated from the hepatopancreas of the New Zealand greenshell mussel Perna canaliculus.518 10 Tunicates (ascidians) Although the most characteristic metabolites of ascidians are alkaloids there are always a few notable exceptions.Phallusides 1–4 716–719 are glucosphingolipids from Phallusia fumigata from Cádiz Spain.519 A series of macrolides lobatamides A–F 720–725 were isolated as the cytotoxic constitents of Aplydium lobatum and a deep water Aplydium species both from Australia and from an unidentified Philippines ascidian.520 An Indonesian Botryllus sp. contained the brominated phenolic metabolites cadiolides A 726 and B 727 together with the known metabolite rubrolide A.521 Rubrolides C 728 and E 729 which are metabolites of Ritterela rubra,522 have been synthesized using a Suzuki cross-coupling reaction to construct the furanone ring.523 The total synthesis of lissoclino-lide 730 which was isolated from Lissoclinum patella,524 also involved cross-coupling reactions.525 Minalemines A–F 731–736 named in memory of the late Professor Luigi Minale who was Europe’s leading marine natural products chemist are guanidine-containing linear peptides three of which also incorporate a rare sulfamic acid residue that were found in Didemnum rodriguesi from New Caledonia.526 The cyclic hexapeptides comoramides A 737 and B 738 and the cyclic heptapeptides mayotamides A 739 and B 740 were obtained from two separate collections of D.molle from Mayotte lagoon in the Comoros.527 The absolute stereochemistry of one of the two valine residues in cyclodidemnamide 741 which is a cyclic peptide from D.molle,528 has been revised from l-Val to d-Val as a result of total synthesis of the both isomers.529,530 Four additional cyclic peptides patellamide G 742 and ulithiacyclamides E–G 743–745 were isolated together with known members of these series from a specimen of Lissoclimun patella from Pohnpei.531 Rhopaladins A–D 746–749 one of which rhopaladin B 747 inhibited cyclin dependent kinase 4 and c-erbB-2 kinase are bis-indole alkaloids from an Okinawan Rhopalaea species.532 Didemnum granulatum from Brazil contained the G2 cell cycle checkpoint inhibitors granulatimide 750 and isogranulatimide 751 the structures of which were confirmed by synthesis and didemnimide E 752 together with known didemnimides.533 Didemnimides A 753 and B 754 which are constituents of D.conchyliatum,534 have been synthesized in an efficient man- Nat. Prod. Rep. 2000 17 7–55 41 ner.535 The structure of the indole alkaloid 755 from Dendrodoa grossularia from Brittany was determined using an X-ray crystallographic study of derivative 756 formed upon acetylation. 536 Meridianins A–E 757–761 are cytotoxic indole alkaloids isolated from Aplydium meridianum collected by trawling near the South Georgia Islands.537 Pseudodistoma aureum from Heron Reef Australia contained eudistomin V 762 together with known members of the eudistomin series.538 Eudistomidin-A 763 which is a calmodulin antagonist from Eudistoma Nat. Prod. Rep.2000 17 7–55 42 glaucus,539 has been synthesized using a very practical scheme.540 Arborescidines A–C 764–766 which are metabolities of Pseudodistoma aborescens,541 have been synthesized as their racemates.542 The presumed C-7 epimer of arborescidine C 766 does not have same spectral data as those reported for the expected product arborescidine D.542 The Indonesian ascidian Eusynstyela latericius contained four mildly cytotoxic pyridoacridine alkaloids styelsamines A– D 767–770.543 Shermilamines D 771 and E 772 were isolated together with tintamine 773 which possesses a new heterocyclic skeleton from Cystodytes violatinctus from the Comoros Islands.544 Arnoamines A 774 and B 775 are cytotoxic pentacyclic pyridoacridine alkaloids from a Cystodytes sp.from Arno Atoll Micronesia.545 Meridine 776 which is a metabolite of Amphicarpa meridiana,546 and cystodamine 777 a cytotoxin from Cystodytes delle chiajei,547 were synthesized using a hetero Diels–Alder reaction as the key step.548 Pantherinine 778 which is a cytotoxic pyridoacridine alkaloid from Aplydium pantherinum,549 was synthesized using a biaryl crosscoupling reaction.550 The New Zealand ascidian Cnemidocarpa bicornuta contained the simple metabolite 3-bromotyramine 779 previously known only as a synthetic chemical.551 Aplydiamine 780 from an Aplidiopsis sp.552 was synthesized by alkylation of 8-oxoadenosine.553 A Spanish Aplydium sp. contained an additional cytotoxic prenylated hydroquinone 781.554 A specimen of Ritterella rete obtained by dredging (300 m below sea level) near New Caledonia contained the cytotoxic sesquiterpene 8-hydroxydendrolasin 782 and five related sesquiterpenes 783–787.555 11 Echinoderms Five cerebrosides CE-1-1 788 CE-1-2 789 CE-1-3 790 CE- 3-1 791 and CE-3-2 792 which are toxic to brine shrimp and a ganglioside CG-1 793 which exhibited neuritogenic activity toward the rat pheochromocytoma PC-12 cell line were obtained from the Japanes sea cucumber Cucumaria echinata.556 Similar neuritogenic activity was recorded for three gangliosides HPG-1 794 HPG-3 795 and HPG-8 796 isolated from the sea cucumber Holothuria pervicax from Japan.557 Two 43 Nat. Prod. Rep. 2000 17 7–55 glucosylceramides 797 and 798 were found together with a known analogue from an Argentinian seastar Cosmasterias lurida.558 Three ceramides AC-1-6 799 AC-1-10 800 and AC- 1-11 801 were obtained from Acanthaster planci from Japan.559 The cerebrosides acanthacerebroside A 802 and astrocerebroside A 803 from the starfish Acanthaster planci560 and Astropecten latespinosus,561 respectively were synthesized via a chiral epoxide derived from L-quebrachitol.562 Two steroidal xylosides 804 and 805 were isolated together with 4-acetoxypyrazole 806 from the sea cucumber Synapta muculata collected in the Andamman and Nicobar Islands.563 Three additional sulfated polyhydroxylated sterols (20R)- cholesta-5,24-diene-2b,3a,21-triol 2,21-disulfate 807 (20R)- 5a-cholest-24-ene-2b,3a,21-triol 3,21-disulfate 808 and (20R)- cholesta-5,24-diene-2a,3a,4b,21-tetraol 3,21-disulfate 809 Nat.Prod. Rep. 2000 17 7–55 44 were isolated from the Antarctic ophiuroid Astrotoma agassizii. 564 The starfish Pteraster tesselatus contained three similar sterol disulfates (20R,25R)-24-methyl-5a-cholesta- 24(28)-ene-2b,3a,21,26-tetraol 3,21-disulfate 810 (20R 25R,S)-cholest-5-ene-2b,3a,21,26-tetraol 2,21-disulfate 811 and (20R,25R)-5a-cholestane-2b,3a,21,26-tetraol 3,21-disulfate 812 an observation that has interesting chemotaxonomic implications.565 The seastar Luidiaster dawsoni from the Sea of Okhotsk contained (24S,25R)-24-methylcholestane- 3b,5a,6b,15a,16b,26-hexaol 813.566 (25R)-5a-cholestane- 3b,6b,15a,16b,26-pentaol 814 which was isolated as a cytotoxic constituent of an Antarctic starfish,567 has been synthesized from diosgenin in good overall yield.568 Asteriidosides A–I 815–823 and L 824 are moderately cytotoxic steroidal saponins with varying numbers of sugar 45 Nat.Prod. Rep. 2000 17 7–55 residues that were isolated from an unidentified Antarctic starfish of the family Asteriidae.569 An additional triterpene glycoside frondoside C 825 was obtained from the Arctic sea cucumber Cucumaria frondosa.570 Two further sterol sulfates 826 and 827 were isolated from an unidentified Holothuria sp. from the Indian Ocean.571 12 Miscellaneous Although they are not strictly natural products the small peptides megabalanein A which contains only 15 amino acid residues and megabalanein B with four additional residues are of interest because they were isolated from the barnacle Megabalanus volcano after treatment with high levels of cadmium.572,573 The monoacyl glycerol 828 has been demonstrated to induce settling and metamorphosis of the larvae of the polychaete worm Hydroides ezoensis on adult tube clumps.574 The Nat.Prod. Rep. 2000 17 7–55 46 pheromone responsible for sperm release in the the polychaete Platynereis dumerilii was shown to be uric acid.575 Two additional cytotoxins cephalostatins 18 829 and 19 830 were isolated as minor metabolites of the South African tube worm Cephalodiscus gilchristi.576 As part of a paper that reports significant activity for hybrid analogues the structure of cepahalostatin 1 831 which is a potent cytotoxin from C. gilchristi,577 was confirmed by total synthesis using a convergent route.578 Two additional ciguatoxin analogues 2,3-dihydro-CTX-3C 832 and 51-hydroxy-CTX-3C 833 which are probably derived from metabolites of the dinoflagellate Gambierdiscus toxicus were found to have accumulated in the viscera of the moray eel Gymnothorax javanicus.579 The structures of the Caribbean ciguatoxins C-CTX-1 834 and C-CTX-2 835 which were obtained from the horse-eye jack Caranx latus are reminiscent of other ciguatoxins and differ mainly by the presence of an additional ring.580 The bile of the sunfish Mola mola contained four sulfates (25S)- and (25R)-3a,7a,11a,26-tetrahydroxy-5bcholestan-27-yl sodium sulfate 836 and (25S)- and (25R)- 3a,7a,12a,26-tetrahydroxy-5b-cholestan-27-yl sodium sulfate 837 together with the taurine conjugate 838.581 Confirmation of the structure and determination of the absolute stereochemistry of lipogrammistin-A 839 which was isolated from the skin secretions of the soapfish Diploprion bifasciatum and Aulacocephalus temmincki,582 have been accomplished as a result of total synthesis.583 Squalamine 840 which is an antiangiogenic antitumor agent from the dogfish shark Squalus acanthius,584 has been synthesized using a readily accessible 47 Nat.Prod. Rep. 2000 17 7–55 spermidine equivalent.585 The Bangladeshi freshwater pufferfish Tetraodon cutcutia contained carbamoyl-N-methylsaxitoxin 841.586 13 References 1 D. J. Faulkner Nat. Prod. Rep. 1999 16 155. 2 J.-M. Kornprobst C. Sallenave and G.Barnathan Comp. Biochem. Physiol. Sect. B 1998 119 1. 3 A. D. Rodríguez E. Gonzalez and C. Ramírez Tetrahedron 1998 54 11683. 4 P. Bernardinelli and L. A. Paquette Heterocycles 1998 49 531. 5 N. Matzanke R. J. Gregg and S. M. Weinreb Org. Prep. Proced. Int. 1998 30 1. 6 C. A. Bewley and D. J. Faulkner Angew. Chem. Int. Ed. 1998 37 2162. 7 Y. Venkateswarlu P. Ramesh and N. S. Reddy Nat. Prod. Sci. 1998 4 115. 8 M. A. Biabani and H. Laatsch J. Prakt. Chem. 1998 340 589. 9 N. Fusetani Biofouling 1998 12 3. 10 A. Kelecom J. Braz. Chem. Soc. 1998 9 101. 11 R. Osinga J. Tramper and R. H. Wijffels Trends Biotechnol. 1998 16 130. 12 G. Cimino and M. T. Ghiselin Chemoecology 1998 8 51. 13 M. E. Hay J. J. Stachowicz E. Cruz-Rivera S. Bullard M.S. Deal and N. Lindquist in Methods in Chemical Ecology Vol 2. Bioassay Methods eds. K. F. Haynes and J. G. Millar Chapman and Hall New York 1998 pp. 39-14. 14 C. Debitus G. Guella I. Mancini J. Waikedre J.-P. Guemas J. L. Nicolas and F. Pietra J. Mar. Biotechnol. 1998 6 136. 15 H. K. Lee D.-S. Lee J. Lim J. S. Kim K. S. Im and J. H. Jung Arch. Pharm. Res. 1998 21 729. 16 S. G. Batrakov D. I. Nikitin V. I. Sheichenko and A. O. Ruzhitsky Biochim. Biophys. Acta 1998 1391 79. 17 M. A. F. Biabani M. Baake B. Lovisetto H. Laatsch E. Helmke and H. Weyland J. Antibiot. 1998 51 333. 18 P. W. Ford M. Gadepalli and B. S. Davidson J. Nat. Prod. 1998 61 1232. 19 S. Omura H. Tanaka Y. Okada and H. Marumo J. Chem. Soc. Chem. Commun. 1976 320. 20 J.A. Trischman P. R. Jensen and W. Fenical Nat. Prod. Lett. 1998 11 279. 21 R. Zinkernagle and M. Koenig Seifen-oele-fette wachse 1967 93 670. 22 V. Bultel-Poncé C. Debitus J.-P. Berge C. Cerceau and M. Guyot J. Mar. Biotechnol. 1998 6 233. 23 R. G. Powell C. R. Smith D. Weisleder G. Matsumoto J. Clardy and J. Kozlowski J. Am. Chem. Soc. 1983 105 3739. 24 C. Acebal R. Alcazar L. M. Cañedo F. De la Calle P. Rodriguez F. Romero and J. L. Fernandez Puentes J. Antibiot. 1998 51 64. 25 J. M. Cronan Jr. T. R. Davidson F. L. Singleton R. R. Colwell and J. H. Cardellina II Nat. Prod. Lett. 1998 11 271. 26 S. Takaishi N. Tuchiya A. Sato T. Negishi Y. Takamatsu Y. Matsushita T. Watanabe Y. Iijima H. Haruyama T. Kinoshita M. Tanaka and K. Kodama J.Antibiot. 1998 51 805. 27 A. B. Smith III and G. R. Ott J. Am. Chem. Soc. 1998 120 3935. 28 K. Gustafson M. Roman and W. Fenical J. Am. Chem. Soc. 1989 111 7519. Nat. Prod. Rep. 2000 17 7–55 48 29 S. D. Rychnovsky D. J. Skalitzky C. Pathirana P. R. Jensen and W. Fenical J. Am. Chem. Soc. 1992 114 671. 30 Y. Kim R. A. Singer and E. M. Carreira Angew. Chem. Int. Ed. 1998 37 1261. 31 A. Numata M. Iritani T. Yamada K. Minoura E. Matsumura T. Yamori and T. Tsuruo Tetrahedron Lett. 1997 38 8215. 32 T. J. Donohoe K. Blades M. Helliwell M. J. Waring and N. J. Newcombe Tetrahedron Lett. 1998 39 8755. 33 R. T. Reid D. H. Live D. J. Faulkner and A. Butler Nature 1993 366 455. 34 J. Deng Y. Hamada and T. Shioiri Synthesis 1998 627. 35 J. Needham M.T. Kelly M. Ishige and R. J. Andersen J. Org. Chem. 1994 59 2058. 36 S. G. Davies and D. J. Dixon J. Chem. Soc. Perkin Trans. 1 1998 2635. 37 P. R. Burkholder R. M. Pfister and F. H. Leitz Appl. Microbiol. 1996 14 649. 38 R. J. Andersen M. S. Wolfe and D. J. Faulkner Mar. Biol. 1974 27 281. 39 H. Laatsch and H. Pudliener Liebigs Ann. Chem. 1989 863. 40 Z. Xu and X. Lu J. Org. Chem. 1998 63 5031. 41 G. N. Belofsky P. R. Jensen M. K. Renner and W. Fenical Tetrahedron 1998 54 1715. 42 G.-Y.-S. Wang L. F. Abrell A. Avelar B. M. Borgeson and P. Crews Tetrahedron 1998 54 7335. 43 M. K. Renner P. R. Jensen and W. Fenical J. Org. Chem. 1998 63 8346. 44 T. Amagata Y. Usami K. Minoura T. Ito and A. Numata J. Antibiot. 1998 51 33. 45 K.A. Alvi A. Casey and B. G. Nair J. Antibiot. 1998 51 515. 46 T. Amagata K. Minoura and A. Numata J. Antibiot. 1998 51 432. 47 K. M. Jenkins S. G. Toske P. R. Jensen and W. Fenical Phytochemistry 1998 49 2299. 48 L. Rahbæk S. Sperry J. E. Piper and P. Crews J. Nat. Prod. 1998 61 1571. 49 C. Iwamoto K. Minoura S. Hagishita K. Nomoto and A. Numata J. Chem. Soc. Perkin Trans. 1 1998 449. 50 S. Sperry G. J. Samuels and P. Crews J. Org. Chem. 1998 63 10011. 51 K. Liberra R. Jansen and U. Lindequist Pharmazie 1998 53 578. 52 H. Onuki H. Miyashige H. Hasegawa and S. Yamashita J. Antibiot. 1998 51 442. 53 T. Amagata M. Doi T. Ohta K. Minoura and A. Numata J. Chem. Soc. Perkin Trans. 1 1998 3585. 54 T. Amagata K. Minoura and A. Numata Tetrahedron Lett.1998 39 3773. 55 J. Breinholt G. W. Jensen R. I. Nielsen C. E. Olsen and J. C. Frisvad J. Antibiot. 1993 46 1101. 56 G. Schlingmann L. Milne D. R. Williams and G. T. Carter J. Antibiot. 1998 51 303. 57 S. G. Toske P. R. Jensen C. A. Kauffmann and W. Fenical Tetrahedron 1998 54 13459. 58 K. M. Jenkins M. K. Renner P. R. Jensen and W. Fenical Tetrahedron Lett. 1998 39 2463. 59 P. Lorenz P. R. Jensen and W. Fenical Nat. Prod. Lett. 1998 12 55. 60 H. Shigemori M. Tenma K. Shimazaki and J. Kobayashi J. Nat. Prod. 1998 61 696. 61 C.-B. Cui H. Kakeya G. Okada R. Onose M. Ubukata I. Takahashi K. Isono and H. Osada J. Antibiot. 1995 48 1382. 62 S. Zhao T. Gan P. Yu and J. M. Cook Tetrahedron Lett. 1998 39 7009. 63 B. Márquez P. Verdier-Pinard E.Hamel and W. H. Gerwick Phytochemistry 1998 49 2387. 64 W. H. Gerwick P. J. Proteau D. G. Nagle E. Hamel A. Blokhin and D. L. Slate J. Org. Chem. 1994 59 1243. 65 J. C. Muir G. Pattenden and T. Ye Tetrahedron Lett. 1998 39 2861. 66 N. Sitachitta and W. H. Gerwick J. Nat. Prod. 1998 61 681. 67 M. A. Graber and W. H. Gerwick J. Nat. Prod. 1998 61 677. 68 G. J. Hooper J. Orjala R. C. Schatzman and W. H. Gerwick J. Nat. Prod. 1998 61 529. 69 G. R. Pettit Y. Kamano H. Kizu C. Dufresne C. L. Herald R. J. Bontemps J. M. Schmidt F. E. Boettner and R. A. Nieman Heterocycles 1989 28 553. 70 G. G. Harrigan W. Y. Yoshids R. E. Moore D. G. Nagle P. U. Park J. Biggs V. J. Paul S. L. Mooberry T. H. Corbett and F.A. Valeriote J. Nat. Prod. 1998 61 1221.71 G. G. Harrigan H. Luesch W. Y. Yoshida R. E. Moore D. G. Nagle V. J. Paul S. L. Moobery T. H. Corbett and F.A. Valeriote J. Nat. Prod. 1998 61 1075. 72 G. R. Pettit Y. Kamano C. L. Herald A. A. Tuinman F. E. Boettner H. Kizu J. M. Schmidt L. Baczynskyj K. B. Tomer and R. J. Bontemps J. Am. Chem. Soc. 1987 109 6883. 73 W. Y. Yoshida and P. J. Scheuer Heterocycles 1998 47 1023. 74 O. Papendorf G. M. König and A. D. Wright Phytochemistry 1998 49 2383. 75 J. H. Cardellina II R. E. Moore E. V. Arnold and J. Clardy J. Org. Chem. 1979 44 4039. 76 S. Ohira T. Ida M. Moritani and T. Hasegawa J. Chem. Soc. Perkin Trans. 1 1998 293. 77 E. Winter and D. Hoppe Tetrahedron 1998 54 10329. 78 N. Maezaki Y. Matsumori T. Shogaki M. Soejima H.Ohishi T. Tanaka and C. Iwata Tetrahedron 1998 54 13087. 79 K. Matsuo T. Matsumoto and K. Nishiwaki Heterocycles 1998 48 1213. 80 I. Tanaka S. Matsuoka M. Murata and K. Tachibana J. Nat. Prod. 1998 61 685. 81 C. B. Rao A. S. R. Anjaneyulu N. S. Sarma Y. Venkateswarlu R. M. Rosser D. J. Faulkner H. M. H. Chen and J. Clardy J. Am. Chem. Soc. 1984 106 7983. 82 H. Nakamura Y. Kawase K. Maruyama and A. Murai Bull. Chem. Soc. Jpn. 1998 71 781. 83 T. Kubota M. Tsuda Y. Doi A. Takahashi H. Nakamichi M. Ishibashi E. Fukushi J. Kawabata and J. Kobayashi Tetrahedron 1998 54 14455. 84 M. Daiguji M. Satake K. J. James A. Bishop L. MacKenzie H. Naoki and T. Yasumoto Chem. Lett. 1998 653. 85 J. Kobayashi H. Shigemori M. Ishibashi T. Yamasu H. Hirota and T.Sasaki J. Org. Chem. 1991 56 5221. 86 D. R. Williams and W. S. Kissel J. Am. Chem. Soc. 1998 120 11198. 87 A. V. K. Prasad and Y. Shimizu J. Am. Chem. Soc. 1989 111 6476. 88 I. Kadota and Y. Yamamoto J. Org. Chem. 1998 63 6597. 89 R. Wang and Y. Shimizu J. Chem. Soc. Chem. Commun. 1990 413. 90 H. Miyaoka M. Tamura and Y. Yamada Tetrahedron Lett. 1998 39 621. 91 G. Guella F. Dini and F. Pietra Helv. Chim. Acta 1995 78 1747. 92 G. Rosini F. Laffi E. Marotta H. Pagani and P. Righi J. Org. Chem. 1998 63 2389. 93 I. Mancini G. Guella A. Defant M. L. Candenas C. P. Armesto D. Depentori and F. Pietra Helv. Chim. Acta 1998 81 1681. 94 J.-Y. Su X.-H. Xu L.-M. Zeng M.-Y. Wang N. Lu Y. Lu and Q.-T. Zhang Phytochemistry 1998 48 583. 95 P.R. Jensen K. M. Jenkins D. Porter and W. Fenical Appl. Envir. Microb. 1998 64 1490. 96 R. J. Capon R. A. Barrow S. Rochfort M. Jobling C. Skene E. Lacey J. H. Gill T. Friedel and D. Wadsworth Tetrahedron 1998 54 2227. 97 R. G. Warren R. J. Wells and J. F. Blount Aust. J. Chem. 1980 33 891. 98 Z.-M. Wang and M. Shen J. Org. Chem. 1998 63 1414. 99 J. A. Pettus Jr. and R. E. Moore J. Am. Chem. Soc. 1971 93 3087. 100 H. Imogaï G. Bernardinelli C. Gränicher M. Moran J.-C. Rossier and P. Müller Helv. Chim. Acta 1998 81 1754. 101 N. Tsuchiya A. Sato H. Haruyama T. Watanabe and Y. Iijima Phytochemistry 1998 48 1003. 102 J. J. Fernández G. Navarro and M. Norte Nat. Prod. Lett. 1998 12 285. 103 B. Bian and I. A. van Altena Aust. J. Chem.1998 51 1157. 104 W. Fenical J. J. Sims D. Squatrito R. M. Wing and P. Radlick J. Org. Chem. 1973 38 2383. 105 H. Akita M. Nozawa and H. Shimizu Tetrahedron Asymmetry 1998 9 1789. 106 W. H. Gerwick W. Fenical N. Fritsch and J. Clardy Tetrahedron Lett. 1979 20 145. 107 A. Abad C. Agulló M. Arnó A. C. Cuñat B. Meseguer and R. J. Zaragozá J. Org. Chem. 1998 63 5100. 108 M. Zarraga P. Arroyo and M. Norte Bol. Soc. Chil. Quim. 1997 43 73. 109 C. Francisco G. Combaut J. Teste and M. Prost Phytochemistry 1978 17 1003. 110 G. Combaut L. Codomier and J. Teste Phytochemistry 1981 20 2036. 111 J .F. Biard J. F. Verbist R. Floch and Y. Letourneux Tetrahedron Lett. 1980 21 1849. 112 J. Li J. Lan Z. Liu and Y. Li J. Nat. Prod. 1998 61 92. 113 G.Barnathan N. Bourgougnon and J.-M. Kornprobst Phytochemistry 1998 47 761. 114 K. Ohta Y. Mizushina N. Hirata M. Takemura F. Sugawara A. Matsukage S. Yoshida and K. Sakaguchi Chem. Pharm. Bull. 1998 46 684. 115 Y. Kan T. Fujita H. Nagai B. Sakamoto and Y. Hokama J. Nat. Prod. 1998 61 152. 116 H. Nagai T. Yasumoto and Y. Hokama J. Nat. Prod. 1997 60 925. 117 H. Nagai Y. Kan T. Fujuita T. Yasumoto and Y. Hokama Biosci. Biotechnol. Biochem. 1998 62 1011. 118 A. F. Rose P. J. Scheuer J. P. Springer and J. Clardy J. Am. Chem. Soc. 1978 100 7665. 119 D. G. Nagle and W. H. Gerwick J. Org. Chem. 1994 59 7227. 120 H. Miyaoka T. Shigemoto and Y. Yamada Heterocycles 1998 47 415. 121 M. Yotsu-Yamashita R. L. Haddock and T. Yasumoto J. Am. Chem.Soc. 1993 115 1147. 122 K. Fujiwara A. Murai M. Yotsu-Yamashita and T. Yasumoto J. Am. Chem. Soc. 1998 120 10770. 123 T. Suzuki K. Koizumi M. Suzuki and E. Kurosawa Chem. Lett. 1983 1643. 124 J. Boukouvalas G. Fortier and I.-I. Radu J. Org. Chem. 1998 63 916. 125 M. Cueto J. Darias J. Rovirosa and A. San Martín J. Nat. Prod. 1998 61 17. 126 M. Cueto J. Darias J. Rovirosa and A. San-Martín Tetrahedron 1998 54 3575. 127 M. Cuerto J. Darias J. Rovirosa and A. San Martín J. Nat. Prod. 1998 61 1466. 128 J. Rovirosa I. Sánchez Y. Palacios J. Darias and A. San Martín Bol. Soc. Chil. Quim. 1990 35 131. 129 P. M. Abreu and J. M. Galindro Indian J. Chem. Sect. B 1998 37 610. 130 A. San Martín R. Negrete and J. Rovirosa Phytochemistry 1991 30 2165.131 P. Rivera V. Manríquez and O. Wittke Acta Crystallogr. Sect. C 1998 54 816. 132 R. W. Fuller J. H. Cardellina II J. Jurek P. J. Scheuer B. Alvarado- Lindmer M. McGuire G. N. Gray J. R. Steiner J. Clardy E. Menez R. H. Shoemaker D. J. Newman K. M. Snader and M. R. Boyd J. Med. Chem. 1994 37 4407. 133 T. Schlama R. Baati V. Gouverneur A. Valleix J. R. Falck and C. Mioskowski Angew. Chem. Int. Ed. 1998 37 2085. 134 G. Guella A. Öztunç I. Mancini and F. Pietra Tetrahedron Lett. 1997 38 8261. 135 E. G. Juagdan R. Kalidindi and P. J. Scheuer Tetrahedron 1997 53 521. 136 M. E. Y. Francisco M. M. Turnbull and K. L. Erickson Tetrahedron Lett. 1998 39 5289. 137 Y. Takahashi M. Suzuki T. Abe and M. Masuda Phytochemistry 1998 48 987.138 K. Kurata K. Taniguchi Y. Agatsuma and M. Suzuki Phytochemistry 1998 47 363. 139 S. Wahidulla L. D’Souza and M. Govenker Phytochemistry 1998 48 1203. 140 Y. Shizuri A. Yamada and K. Yamada Phytochemistry 1984 23 2672. 141 H. Takahashi Y. Tonoi K. Matsumoto H. Minami and Y. Fukuyama Chem. Lett. 1998 485. 142 K. Miyashita A. Tanaka H. Shintaku and C. Iwata Tetrahedron 1998 54 1395. 143 K. Kurata T. Suzuki M. Suzuki E. Kurosawa A. Furusaki and T. Matsumoto Chem. Lett. 1983 299. 144 R. Kazlauskas P. Y. Murphy R. J. Quinn and R. J. Wells Aust. J. Chem. 1976 29 2533. 145 M. Suzuki and E. Kurosawa Bull. Chem. Soc. Jpn. 1979 52 3349. 146 R. R. Izac and J. J. Sims J. Am. Chem. Soc. 1979 101 6136. 147 S. Yoo J. H. Suh and K. Y. Yi Synthesis 1998 771.148 D. Davyt W. Entz R. Fernandez R. Mariezcurrena A. W. Mombrú J. Saldaña L. Domínguez J. Coll and E. Manta J. Nat. Prod. 1998 61 1560. 149 S. Takahashi T. Matsunaga C. Hasegawa H. Saito D. Fujita F. Kiuchi and Y. Tsuda Chem. Pharm. Bull. 1998 46 1527. 150 A. Nishida M. Fuwa Y. Fujikawa E. Nakahata A. Furuno and M. Nakagawa Tetrahedron Lett. 1998 39 5983. 151 N. M. Carballeira R. Colón and A. Emiliano J. Nat. Prod. 1998 61 675. 152 N. M. Carballiera M. Pagán and A. D. Rodríguez J. Nat. Prod. 1998 61 1049. 153 N. M. Carballiera and J. Sepúlveda Lipids 1992 27 72. 154 N. M. Carballiera A. Emiliano N. Hernández-Alonso and F. A. González J. Nat. Prod. 1998 61 1543. 49 Nat. Prod. Rep. 2000 17 7–55 155 T. Hattori K. Adachi and Y.Shizuri J. Nat. Prod. 1998 61 823. 156 Y. Venkateswarlu N. S. Reddy P. Ramesh M. Rama Rao and T. Silva Indian J. Chem. Sect. B 1998 37 1264. 157 E. G. Juagdan R. S. Kalidindi P. J. Scheuer and M. Kelly-Borges Tetrahedron Lett. 1995 36 2905. 158 S. Takanashi M. Tagaki H. Takikawa and K. Mori J. Chem. Soc. Perkin Trans. 1 1998 1603. 159 Y. Guo M. Gavagnin C. Salierno and G. Cimino J. Nat. Prod. 1998 61 333. 160 Y. Seo K. W. Cho J.-R. Rho J. Shin and C. J. Sim Tetrahedron 1998 54 447. 161 J. Shin Y. Seo and K. W. Cho J. Nat. Prod. 1998 61 1268. 162 J. S. Kim K. S. Im J. H. Jung Y.-L. Kim J. Kim C. J. Shim and C.-O. Lee Tetrahedron 1998 54 3151 [erratum Tetrahedron 1999 55 2113]. 163 A. Guerriero C. Debitus D. Laurent M. D’Ambrosio and F.Pietra Tetrahedron Lett. 1998 39 6395. 164 J. Shin Y. Seo K. W. Cho J.-R. Rho and V. J. Paul Tetrahedron 1998 54 8711. 165 F. Rooney and R. J. Capon Lipids 1998 33 639. 166 T. Yosief A. Rudi Y. Wolde-ab and Y. Kashman J. Nat. Prod. 1998 61 491. 167 Y. F. Hallock J. H. Cardellina II M. S. Balaschak M. R. Alexander T. R. Prather R. H. Shoemaker and M. R. Boyd J. Nat. Prod. 1995 58 1801. 168 A. Sharma and S. Chattopadhyay Tetrahedron Asymmetry 1998 9 2635. 169 A. Fontana M. Ishibashi and J. Kobayashi Tetrahedron 1998 54 2041. 170 A. Fontana M. Ishibashi H. Shigemori and J. Kobayashi J. Nat. Prod. 1998 61 1427. 171 R. S. Compagnone I. C. Piña H. R. Rangel F. Dagger A. I. Suárez M. V. R. Reddy and D. J. Faulkner Tetrahedron 1998 54 3057.172 J. C. Braekman D. Daloze S. De Groote J. B. Fernandes and R. W. M. Van Soest J. Nat. Prod. 1998 61 1038. 173 B. Harrison and P. Crews J. Nat. Prod. 1998 61 1033. 174 A. Qureshi J. Salvá M. K. Harper and D. J. Faulkner J. Nat. Prod. 1998 61 1539. 175 Q. Lu and D. J. Faulkner J. Nat. Prod. 1998 61 1096. 176 S. Matsunaga Y. Nogata and N. Fusetani J. Nat. Prod. 1998 61 663. 177 S. Matsunaga T. Sugawara and N. Fusetani J. Nat. Prod. 1998 61 1164. 178 X. Fu F. J. Schmitz M. Kelly-Borges T. L. McCready and C. F. B. Holmes J. Org. Chem. 1998 63 7957. 179 K. G. Steube C. Meyer P. Proksch A. Supriyono W. Sumaryono and H. G. Drexler Anticancer Res. 1998 18 129. 180 Y. Kato N. Fusetani S. Matsunaga K. Hashimoto S. Fujita and T. Furuya J. Am.Chem. Soc. 1986 108 2780. 181 Y. Kato N. Fusetani S. Matsunaga K. Hashimoto and K. Koseki J. Org. Chem. 1988 53 3930. 182 A. B. Smith III G. K. Friestad J. J.-W. Duan J. Barbosa K. G. Hull M. Iwashima Y. Qui P. G. Spoors E. Bertounesque and B. A. Salvatore J. Org. Chem. 1998 63 7596. 183 A. K. Ogawa and R. W. Armstrong J. Am. Chem. Soc. 1998 120 12435. 184 M. Kobayashi S. Aoki K. Gato and I. Kitagawa Chem. Pharm. Bull. 1996 44 2142. 185 G. R. Pettit Z. A. Cichacz F. Gao C. L. Herald M. R. Boyd J. M. Schmidt and J. N. A. Hooper J. Org. Chem. 1993 58 1302. 186 M. W. Hayward R. M. Roth K. J. Duffy P. I. Dalko K. L. Stevens J. Guo and Y. Kishi Angew. Chem. Int. Ed. 1998 37 192. 187 P. A. Searle T. F. Molinski L. J. Brzezinski and J. W. Leahy J.Am. Chem. Soc. 1996 118 9422. 188 C. J. Forsyth F. Ahmed R. D. Cink and C. S. Lee J. Am. Chem. Soc. 1998 120 5597. 189 P. T. Northcote J. W. Blunt and M. H. G. Munro Tetrahedron Lett. 1991 32 6411. 190 R. M. Rzasa H. A. Shea and D. Romo J. Am. Chem. Soc. 1998 120 591. 191 D. Romo R. M. Rzasa H. A. Shea K. Park J. M. Langenhan L. Sun A. Akhiezer and J. O. Liu J. Am. Chem. Soc. 1998 120 12237. 192 N. B. Perry J. W. Blunt M. H. G. Munro and A. M. Thompson J. Org. Chem. 1990 55 223. 193 N. Fusetani T. Sugawara and S. Matsunaga J. Org. Chem. 1992 57 3828. 194 P. J. Kocienski R. Narquizian P. Raubo C. Smith and F. T. Boyle Synlett. 1998 869. 195 P. J. Kocienski R. Narquizian P. Raubo C. Smith and F. T. Boyle Synlett. 1998 1432. Nat.Prod. Rep. 2000 17 7–55 50 196 M. Kobayashi K. Higuchi N. Murakami H. Tajima and S. Aoki Tetrahedron Lett. 1997 38 2859. 197 N. Murakami W. Wang M. Aoki Y. Tsutsui M. Sugimoto and M. Kobayashi Tetrahedron Lett. 1998 39 2349. 198 M. T. Crimmins and B. W. King J. Am. Chem. Soc. 1998 120 9084. 199 E. ter Harr R. J. Kowalski E. Hamel C. M. Lin R. E. Longley S. P. Gunasekera H. S. Rosenkranz and B. W. Day Biochemistry 1996 35 243. 200 J. A. Marshall and B. A. Johns J. Org. Chem. 1998 63 7885. 201 K. Tachibana P. J. Scheuer Y. Tsukitani H. Kikuchi D. Van Engen J. Clardy Y. Gopichand and F. J. Schmitz J. Am. Chem. Soc. 1981 103 2469. 202 N. B. Perry G. Ellis J. W. Blunt T. A. J. Haystead R. J. Lake and M. H. G. Munro Nat. Prod. Lett. 1998 11 305.203 S. F. Sabes R. A. Urbanek and C. J. Forsyth J. Am. Chem. Soc. 1998 120 2534. 204 S. V. Ley A. C. Humphries H. Eick R. Downham A. R. Ross R. J. Boyce J. B .J. Pavey and J. Pietruszka J. Chem. Soc. Perkin Trans. 1 1998 3907. 205 Y. Venkateswarlu M. R. Rao and U. Venkatesham J. Nat. Prod. 1998 61 1388. 206 I. Thirionet D. Daloze J. C. Braekman and P. Willemsen Nat. Prod. Lett. 1998 12 209. 207 M. Assmann V. Wray R. W. M. Van Soest and P. Proksch Z. Naturforsch. Sect. C 1998 53 398. 208 R. Mierzwa A. King M. A. Conover S. Tozzi M. S. Puar M. Patel S. J. Coval and S. A. Pomponi J. Nat. Prod. 1994 57 175. 209 M. S. Butler T. K. Lim R. J. Capon and L. S. Hammon Aust. J. Chem. 1991 44 287. 210 K. Moody R. H. Thomson E. Fattorusso L. Minale and G.Sodano J. Chem. Soc. Perkin Trans. 1 1972 18. 211 H. H. Wassermann and J. Wang J. Org. Chem. 1998 63 5581. 212 R. Kazlauskas R. O. Lidgard P. T. Murphy R. J. Wells and J. F. Blount Aust. J. Chem. 1981 34 765. 213 Z.-W. Guo K. Machiya G. M. Salamonczyk and C. Sih J. Org. Chem. 1998 63 4269. 214 S. Tsukamoto H. Kato H. Hirota and N. Fusetani J. Org. Chem. 1996 61 2936. 215 M. T. Hamann P. J. Scheuer and M. Kelly-Borges J. Org. Chem. 1993 58 6565. 216 R .C. Schoenfeld and B. Ganem Tetrahedron Lett. 1998 39 4147. 217 N. Fusetani T. Sugawara S. Matsunaga and H. Hirota J. Org. Chem. 1991 56 4971. 218 K. Uchida H. Watanabe and T. Kitahara Tetrahedron 1998 54 8975. 219 Y. Venkateswarlu M. A. F. Biabani and J. V. Rao J. Nat. Prod. 1995 58 269.220 G. L. Kad V. Singh A. Khurana and J. Singh J. Nat. Prod. 1998 61 297. 221 X. Fu M. L. G. Ferriera F. J. Schmitz and M. Kelly-Borges J. Nat. Prod. 1998 61 1226. 222 W. F. Tinto A. J. Lough S. McLean W. F. Reynolds M. Yu and W. R. Chan Tetrahedron 1998 54 4451. 223 M. V. R. Reddy M. K. Harper and D. J. Faulkner Tetrahedron 1998 54 10649. 224 J. A. Palermo M. F. R. Brasco E. Cabezas V. Balzaretti and A. M. Seldes J. Nat. Prod. 1998 61 488. 225 A. Randazzo F. Dal Piaz S. Orrù C. Debitus C. Roussakis P. Pucci and L. Gomez-Paloma Eur. J. Org. Chem. 1998 2659. 226 E. W. Schmidt and D. J. Faulkner Tetrahedron 1998 54 3043. 227 Y. Nakao N. Oku S. Matsunaga and N. Fusetani J. Nat. Prod. 1998 61 667. 228 E. W. Schmidt C. A. Bewley and D.J. Faulkner J. Org. Chem. 1998 63 1254. 229 H. Uemoto Y. Yahiro H. Shigemori M. Tsuda T. Takao Y. Shimonishi and J. Kobayashi Tetrahedron 1998 54 6719. 230 D. P. Clark J. Carroll S. Naylor and P. Crews J. Org. Chem. 1998 63 8757. 231 S. Li E. J. Dumdei J. W. Blunt M. H. G. Munro W. T. Robinson and L. K. Pannell J. Nat. Prod. 1998 61 724. 232 G. R. Pettit F. Gao and R. Cerny Heterocycles 1993 35 711. 233 R. B. Bates S. Caldera and M. D. Ruane J. Nat. Prod. 1998 61 405. 234 W. D. Clark T. Corbett F. Valeriote and P. Crews J. Am. Chem. Soc. 1997 119 9285. 235 P. A. Grieco and M. Reilly Tetrahedron Lett. 1998 39 8925. 236 M. Kobayashi S. Aoki N. Obyabu M. Kurosu W. Wang and I. Kitagawa Tetrahedron Lett. 1994 35 7969. 237 J. D. White J.Hong and L. A. Robarge Tetrahedron Lett. 1998 39 8779. 238 H. Arimoto I. Hayakawa M. Kuramoto and D. Uemura Tetrahedron Lett. 1998 39 861. 239 K. C. Bascombe S. R. Peter W. F. Tinto S. M. Bissada S. McLean and W. F. Reynolds Heterocycles 1998 48 1461. 240 W. F. Tinto Heterocycles 1998 48 2089. 241 M. Kobayashi K. Kawazoe and I. Kitagawa Chem. Pharm. Bull. 1989 37 1676. 242 M. Kobayashi Y. Miyamoto S. Aoki N. Murakami I. Kitagawa Y. In and T. Ishida Heterocycles 1998 47 195. 243 J. E. Baldwin A. Melman V. Lee C. R. Firkin and R. C. Whitehead J. Am. Chem. Soc. 1998 120 8559. 244 J. C. Braekman D. Daloze P. Macedo de Abreu C. Piccini-Leopardi G. Germain and M. Van Meerssche Tetrahedron Lett. 1982 23 4277. 245 J. C. Braekman D. Daloze N.Defay and D. Zimmerman Bull. Soc. Chim. Belg. 1984 93 941. 246 J. C. Braekman D. Daloze G. Cimino and E. Trivellone Bull. Soc. Chim. Belg. 1988 97 519. 247 R. W. Scott J. Epperson and C. H. Heathcock J. Org. Chem. 1998 63 5001. 248 C. H. Heathcock R. C. D. Brown and T. C. Norman J. Org. Chem. 1998 63 5013. 249 D. R. Beukes M. T. Davies-Coleman M. Kelly-Borges M. K. Harper and D. J. Faulkner J. Nat. Prod. 1998 61 699. 250 R. J. Capon J. K. MacLeod and P. J. Scammells Tetrahedron 1986 42 6545. 251 J. K. MacLeod A. Ward and A. C. Willis Aust. J. Chem. 1998 51 177. 252 X. Fu F. J. Schmitz R. S. Tanner and M. Kelly-Borges J. Nat. Prod. 1998 61 384. 253 R. J. Capon F. Rooney L. M. Murray E. Collins A. T. R. Sim J. A. P. Rostas M. S. Butler and A.R. Carroll J. Nat. Prod. 1998 61 660. 254 K. Bartik J. C. Braekman D. Daloze C. Stoller J. Huysecom G. Vandevyver and R. Ottinger Can. J. Chem. 1987 65 2118. 255 S. Tsujii K. L. Rinehart Jr. S. P. Gunasekera Y. Kashman S. S. Cross M. S. Lui S. A. Pomponi and M. C. Diaz J. Org. Chem. 1988 53 5446. 256 I. Kawasaki H. Katsuma Y. Nakayama M. Yamashita and S. Ohta Heterocycles 1998 48 1887. 257 C. Eder P. Schupp P. Proksch V. Wray K. Steube C. E. Müller W. Frobenius M. Herderich and R. W. M. van Soest J. Nat. Prod. 1998 258 P. S. Parameswaran C. G. Naik S. Y. Kamat and B. N. Pramanik 259 D. C. Radisky E. S. Radisky L. R. Barrows B. R. Copp R. A. Kramer 260 E. W. Schmidt M. K. Harper and D. J. Faulkner J. Nat. Prod. 1995 261 H. H. Sun S.Sakemi N. Burres and P. McCarthy J. Org. Chem. 262 M. Iwao O. Motoi T. Fukuda and F. Ishibashi Tetrahedron 1998 54 263 M. Alvarez M. A. Bros and J. A. Joule Tetrahedron Lett. 1998 39 61 301. Indian J. Chem. Sect. B 1998 37 1258. and C. M. Ireland J. Am. Chem. Soc. 1993 115 1632. 58 1861. 1990 55 4964. 8999. 679. 264 G. A. Kraus and N. Selvakumar J. Org. Chem. 1998 63 9846. 265 A. D. Patil N. V. Kumar W. C. Kokke M. F. Bean A. J. Freyer C. De Brosse S. Mai A. Truneh D .J. Faulkner B. Carte A. L. Breen R. P. Hertzberg R. K. Johnson J. W. Westley and B. C. M. Potts J. Org. Chem. 1995 60 1182. 266 B. B. Snider and J. Chen Tetrahedron Lett. 1998 39 5697. 267 G. Koren-Goldshlager Y. Kashman and M. Schleyer J. Nat. Prod. 268 D. E. Williams P.Lassota and R. J. Andersen J. Org. Chem. 1998 63 269 F. Kong E. I. Graziani and R. J. Andersen J. Nat. Prod. 1998 61 270 R. J. Clark K. L. Field R. L. Charan M. J. Garson I. M. Brereton and 271 D. Watanabe M. Tsuda and J. Kobayashi J. Nat. Prod. 1998 61 272 M. Tsuda D. Watanabe and J. Kobayashi Tetrahedron Lett. 1998 39 273 G. Cimino A. Spinella and E. Trivellone Tetrahedron Lett. 1989 30 274 Y. Guo E. Trivellone G. Scognamiglio and G. Cimino Tetrahedron 275 Y. Guo E. Trivellone G. Scognamiglio and G. Cimino Tetrahedron 276 R. Sakai T. Higa C. W. Jefford and G. Bernardinelli J. Am. Chem. 1998 61 282. 4838. 267. A. C. Willis Tetrahedron 1998 54 8811. 689. 1207. 133. Lett. 1998 39 463. 1998 54 541. Soc. 1986 108 6404. 277 M.Tsuda N. Kawasaki and J. Kobayashi Tetrahedron 1994 50 7957. 278 K. Kondo H. Shigemori Y. Kikuchi M. Ishibashi T. Sasaki and J. Kobayashi J. Org. Chem. 1992 57 2480. 279 J. D. Winkler and J. M. Axten J. Am. Chem. Soc. 1998 120 6425. 280 N. Fusetani N. Asai S. Matsunaga K. Honda and K. Yasumuro Tetrahedron Lett. 1994 35 3967. 281 M .J. Wanner and G.-J. Koomen Eur. J. Org. Chem. 1998 889. 282 J. E. Baldwin D. R. Spring C. E. Atkinson and V. Lee Tetrahedron 1998 54 13655. 283 N. Fusetani K. Yasumuro S. Matsunaga and H. Hirota Tetrahedron Lett. 1989 30 6891. 284 Y. Morimoto C. Yokoe H. Kurihara and T. Kinoshita Tetrahedron 1998 54 12197. 285 J. E. Baldwin and R. C. Whitehead Tetrahedron Lett. 1992 33 2059. 286 J. E. Baldwin T. D. W. Claridge A.J. Culshaw F. A. Heupel V. Lee D. R. Spring R. C. Whitehead R. J. Boughtflower I. M. Mutton and R. J. Upton Angew. Chem. Int. Ed. 1998 37 2661. 287 S. Forenza L. Minale R. Riccio and E. Fattorusso J. Chem. Soc. Chem. Commun. 1971 1129. 288 G. M. König A. D. Wright and A. Linden Planta. Med. 1998 64 443. 289 T. Iwagawa M. Kaneko H. Okamura M. Nakatani and R. W. M. Van Soest J. Nat. Prod. 1998 61 1310. 290 I. Mancini G. Guella P. Amade C. Roussakis and F. Pietra Tetrahedron Lett. 1997 38 6271. 291 A. Umeyama S. Ito E. Yuasa S. Arihara and T. Yamada J. Nat. Prod. 1998 61 1433. 292 F. Cafieri E. Fattorusso and O. Taglialatela-Scafati J. Nat. Prod. 1998 61 122. 293 C.-J. Li F. J. Schmitz and M. Kelly-Borges J. Nat. Prod. 1998 61 387.294 K. Inaba H. Sato M. Tsuda and J. Kobayashi J. Nat. Prod. 1998 61 693. 295 X. Shen T. L. Perry C. D. Dunbar M. Kelly-Borges and M. T. Hamann J. Nat. Prod. 1998 61 1302. 296 M. D’Ambrosio A. Guerriero C. Debitus O. Ribes J. Pusset S. Leroy and F. Pietra J. Chem. Soc. Chem. Commun. 1993 1305. 297 T. W. Hong D. R. Jíminez and T. F. Molinski J. Nat. Prod. 1998 61 158. 298 R. B. Kinnel H.-P. Gehrken and P. J. Scheuer J. Am. Chem. Soc. 1993 115 3376. 299 R. B. Kinnel H.-P. Gehrken R. Swali G. Skoropowski and P. J. Scheuer J. Org. Chem. 1998 63 3281. 300 L. Zeng Y. Zhu S. Yan and J. Su Chem. Res. Chin. Univ. 1998 14 426. 301 H. Nakamura Y. Ohizumi J. Kobayashi and Y. Hirata Tetrahedron Lett. 1984 25 2475. 302 T. Lindel and M. Hochgürtel Tetrahedron Lett.1998 39 2541. 303 S. Tsukamoto H. Kato H. Hirota and N. Fusetani Tetrahedron Lett. 1996 37 1439. 304 J. A. Ponasik S. Conova D. Kinghorn W. A. Kinney D. Rittschoff and B. Ganem Tetrahedron 1998 54 6977. 305 E. E. Garcia L. E. Benjamin and R. I. Fryer J. Chem. Soc. Chem. Commun. 1973 78. 306 J. J. Morales and A. D. Rodríguez J. Nat. Prod. 1991 54 629. 307 F. Cafieri E. Fattorusso A. Mangoni and O. Taglialatela-Scafati Tetrahedron Lett. 1996 37 3587. 308 A. Olofson K. Yakushijin and D. A. Horne J. Org. Chem. 1998 63 1248. 309 G. M. König and A. D. Wright Planta Med. 1998 64 88. 310 R. J. Capon S. P. B. Ovenden and T. Dargaville Aust. J. Chem. 1998 51 169. 311 S. Sperry and P. Crews J. Nat. Prod. 1998 61 859. 312 F.Cafieri E. Fattorusso and O. Taglialatela-Scafati J. Nat. Prod. 1998 61 1171. 313 S. Matsunaga T. Kamimura and N. Fusetani J. Nat. Prod. 1998 61 671. 314 B. Moon B. J. Baker and J. B. McClintock J. Nat. Prod. 1998 61 116. 315 A. Ahond M. B. Zurita M. Colin C. Fizames P. Laboute F. Lavelle D. Laurent C. Poupat J. Pusset M. Pusset O. Thoison and P. Potier C. R. Acad. Sci. Paris 1988 307 145. 316 S. Marchais A. Al Mourabit A. Ahond C. Poupat and P. Potier Tetrahedron Lett. 1998 39 8085. 317 F. S. de Guzman B. R. Copp C. L. Mayne G. P. Concepcion G. C. Mangalindan L. R. Barrows and C. M. Ireland J. Org. Chem. 1998 63 8042. 318 G. Cimino S. De Rosa S. De Stefano L. Cariello and L. Zanetti Experientia 1982 38 896. 51 Nat. Prod. Rep. 2000 17 7–55 319 R.Puliti S. De Rosa and C. A. Mattia Acta Crystallogr. Sect. C 1998 54 1954. 320 Y. F. Hallock J. H. Cardellina II and M. R. Boyd Nat. Prod. Lett. 1998 11 153. 321 S. J. Coval M. A. Conover R. Mierzwa A. King M. S. Puar D. W. Phife J.-K. Pai R. E. Burrier H.-S. Ahn G. C. Boykow M. Patel and S. A. Pomponi Bioorg. Med. Chem. Lett. 1995 5 605. 322 A. F. Barrero E. J. Alvarez-Manzaneda and R. Chahboun Tetrahedron 1998 54 5635. 323 F. J. Schmitz V. Lakshmi D. R. Powell and D. van der Helm J. Org. Chem. 1984 49 241. 324 J. C. Anderson and D. J. Pearson J. Chem. Soc. Perkin Trans. 1 1998 2023. 325 R. T. Luibrand T. R. Erdman J. J. Vollmer P. J. Scheuer J. Finer and J. Clardy Tetrahedron 1979 35 609. 326 S. Poigny M. Guyot and M. Samadi J.Org. Chem. 1998 63 5890. 327 Y. Zhu W. Y. Yoshida M. Kelly-Borges and P. J. Scheuer Heterocycles 1998 49 355. 328 H. Nakamura J. Kobayashi M. Kobayashi Y. Ohizumi and Y. Hirata Chem. Lett. 1985 6177. 329 D. M. Roll P. J. Scheuer G. K. Matsumoto and J. Clardy J. Am. Chem. Soc. 1983 105 6177. 330 M. Kobayashi N. Shimizu Y. Kyogoku and I. Kitagawa Chem. Pharm. Bull. 1985 33 1305. 331 A. Kojima T. Takemoto M. Sodeoka and M. Shibasaki Synthesis 1998 581. 332 F. Miyazaki K. Uotsu and M. Shibasaki Tetrahedron 1998 54 13073. 333 M. Balbin-Oliveros R. A. Edrada P. Proksch V. Wray L. Witte and R. W. M. Van Soest J. Nat. Prod. 1998 61 948. 334 R. Sakowicz M. S. Berdelis K. Ray C. L. Blackburn C. Hopmann D. J. Faulkner and L. S. B. Goldstein Science 1998 280 292.335 A. E. Flowers M .J. Garson K. A. Byriel and C. H. L. Kennard Aust. J. Chem. 1998 51 195. 336 Y. Venkateswarlu N. S. Reddy and P. Ramesh Nat. Prod. Sci. Korea 1998 4 158. 337 H. Hirota T. Okino E. Yoshimura and N. Fusetani Tetrahedron 1998 54 13971. 338 X. Fu J. R. Barnes M. B. Hossain F. J. Schmitz and D. Van der Helm Nat. Prod. Lett. 1998 12 75. 339 A. Montagnac M.-T. Martin C. Debitus and M. Païs J. Nat. Prod. 1996 59 866. 340 T. Nakano J. Villamizar and M. A. Maillo J. Chem. Res. (S) 1998 560. 341 A. E. Wright S. A. Pomponi O. J. McConnell S. Khomoto and P. J. McCarthy J. Nat. Prod. 1987 50 976. 342 T. Suguhara and K. Ogasawara Tetrahedron Asymmetry 1998 9 2215. 343 C. Fuganti and S. Serra Synlett 1998 1252.344 G. Cimino S. De Stefano A. Guerriero and L. Minale Tetrahedron Lett. 1975 1425. 345 A. M. Moiseenkov A. A. Surkova A. V. Lozanova and V. V. Veselovsky Russ. Chem. Bull. 1997 46 1956. 346 L. M. West P. T. Northcote and C. N. Battershill Aust. J. Chem. 1998 51 1097. 347 C.-J. Li F. J. Schmitz and M. Kelly-Borges J. Nat. Prod. 1998 61 546. 348 M. R. Kernan R. C. Cambie and P. R. Bergquist J. Nat. Prod. 1990 53 724. 349 T. W. Hambley A. Poiner and W. C. Taylor Aust. J. Chem. 1990 43 1861. 350 G. Pattenden L. Roberts and A. J. Blake J. Chem. Soc. Perkin Trans. 1 1998 863. 351 N. H. Tran J. N. A. Hooper and R. J. Capon Aust. J. Chem. 1995 48 1757. 352 K. Gerlach and H. M. R. Hoffmann Synlett 1998 682. 353 A. Umeyama M. Nozaki and S.Arihara J. Nat. Prod. 1998 61 945. 354 A. Umeyama M. Machida M. Nozaki and S. Arihara J. Nat. Prod. 1998 61 1435. 355 D. Wolf and F. J. Schmitz J. Nat. Prod. 1998 61 1524. 356 H. Miyaoka M. Shimomura H. Kimura Y. Yamada H.-S. Kim and Y. Wataya Tetrahedron 1998 54 13467. 357 X. Fu F. J. Schmitz R. S. Tanner and M. Kelly-Borges J. Nat. Prod. 1998 61 548. 358 T. Yosief A. Rudi Z. Stein I. Goldberg G. M. D. Gravalos M. Schleyer and Y. Kashman Tetrahedron Lett. 1998 39 3323. 359 S. Sperry F. A. Valeriote T. H. Corbett and P. Crews J. Nat. Prod. 1998 61 241. Nat. Prod. Rep. 2000 17 7–55 52 360 M. D’Ambrosio A. Guerriero E. Deharo C. Debitus V. Munoz and F. Pietra Helv. Chim. Acta 1998 81 1285. 361 R. J. Capon S. J. Rochfort S. P.B. Ovenden and R. P. Metzger J. Nat. Prod. 1998 61 525. 362 S. P. B. Ovenden and R. J. Capon Aust. J. Chem. 1998 51 573. 363 M. Yanai S. Ohta E. Ohta and S. Ikegami Tetrahedron 1998 54 15607. 364 S. Ohta M. Uno M. Yoshimura Y. Hiraga and S. Ikegami Tetrahedron. Lett. 1996 37 2265. 365 R. Takagi A. Sasaoka H. Nishitani S. Kojima Y. Hiraga and K. Ohkata J. Chem. Soc. Perkin Trans. 1 1998 925. 366 M. R. Kernan and D. J. Faulkner J. Org. Chem. 1988 53 4574. 367 L. V. Manes P. Crews M. R. Kernan D. J. Faulkner F. R. Fronczek and R. D. Gandour J. Org. Chem. 1988 53 570. 368 J. Kimura E. Ishizuka Y. Nakao W. Y. Yoshida P. J. Scheuer and M. Kelly-Borges J. Nat. Prod. 1998 61 248. 369 A. Carotenuto E. Fattorusso V. Lanzotti S. Magno R. Carnuccio and T.Iuvone Comp. Biochem. Physiol. 1998 119C 119. 370 S. De Rosa A. Crispino A. De Giulio C. Iodice R. Benrezzouk M. C. Terencio M. L. Ferrándiz M. J. Alcaraz and M. Payá J. Nat. Prod. 1998 61 931. 371 A. Randazzo C. Debitus L. Minale P. G. Pastor M. J. Alcaraz M. Payá and L. Gomez-Paloma J. Nat. Prod. 1998 61 571. 372 R. C. Cambie P. S. Rutledge X.-S. Yang and P. R. Bergquist J. Nat. Prod. 1998 61 1416. 373 S. De Rosa A. Crispino A. De Giulio C. Iodice G. Tommonaro and N. Zavodnik Tetrahedron 1998 54 6185. 374 N. Tsuchiya A. Sato T. Hata N. Sato K. Sasagawa and T. Kobayashi J. Nat. Prod. 1998 61 468. 375 G. R. Pettit Z. A. Cichacz R. Tan M. S. Hoard N. Melody and R. K. Pettit J. Nat. Prod. 1998 61 13. 376 G. R. Pettit R. Tan N. Melody Z.A. Cichacz D. L. Herald M. S. Hoard R. K. Pettit and J.-C. Chapuis Bioorg. Med. Chem. Lett. 1998 8 2093. 377 A. Rueda E. Zubía M. J. Ortega J. L. Carballo and J. Salvá J. Nat. Prod. 1998 61 258. 378 Y. Wan Q. Li L. Zeng and J. Su Acta Sci. Nat. Univ. Sunyatseni 1998 37 81. 379 S. P. Gunasekera P. J. McCarthy M. Kelly-Borges E. Lobkovsky and J. Clardy J. Am. Chem. Soc. 1996 118 8759. 380 J. Boukouvalas Y.-X. Cheng and J. Robichaud J. Org. Chem. 1998 63 228. 381 S. R. Magnuson L. Sepp-Lorenzino N. Rosen and S. J. Danishefsky J. Am. Chem. Soc. 1998 120 1615. 382 In the previous report in this series the structure of dysidolide was drawn with the incorrect absolute configuration. 383 Y. Kato N. Fusetani S. Matsunaga and K. Hashimoto Experientia 1986 42 1299.384 W. D. Schmitz N. B. Messerschmidt and D. Romo J. Org. Chem. 1998 63 2058. 385 W. Hofheinz and P. Schönholzer Helv. Chim. Acta. 1977 60 1367. 386 R. P. Gregson and D. Ouvrier J. Nat. Prod. 1982 45 412. 387 J. Uenishi R. Kawahama and O. Yonemitsu J. Org. Chem. 1997 62 1691. 388 J. Uenishi R. Kawahama T. Imakoga and O. Yonemitsu Chem. Pharm. Bull. 1998 46 1090. 389 E. D. de Silva and P. J. Scheuer Tetrahedron Lett. 1980 21 1611. 390 J. Coombs E. Lattmann and H. M. R. Hoffmann Synthesis 1998 1367. 391 S. Aoki Y. Yoshioka Y. Miyamoto K. Higuchi A. Setiawan N. Murakami Z.-S. Chen T. Sumizawa S. Akiyama and K. Akiyama Tetrahedron Lett. 1998 39 6303. 392 S. De Marino F. Zollo M. Iorizzi and C. Debitus Tetrahedron Lett.1998 39 7611. 393 S. Tsukamoto S. Matsunaga N. Fusetani and R. W. M. Van Soest J. Nat. Prod. 1998 61 1374. 394 M. V. D’Auria C. Giannini A. Zampella L. Minale C. Debitus and C. Roussakis J. Org. Chem. 1998 63 7382. 395 L. P. Ponomarenko T. N. Makar’eva and V. A. Stonik Russ. Chem. Bull. 1998 47 2017. 396 S. Ohta M. Uno M. Tokumasu Y. Hiraga and S. Ikegami Tetrahedron Lett. 1996 37 7765. 397 H. Hioki M. Hamano Y. Mimura M. Kodama S. Ohta M. Yanai and S. Ikegami Tetrahedron Lett. 1998 39 7745. 398 H. Hioki H. Ooi Y. Mimura S. Yoshio and M. Kodama Synlett 1998 729. 399 A. Rudi Z. Stein I. Goldberg T. Yosief Y. Kashman and M. Schleyer Tetrahedron Lett. 1998 39 1445. 400 X. Xu M. Wang J. Su and L. Zeng Tropic. Oceanology 1998 17 89. 401 K.Iguchi S. Kaneta K. Mori Y. Yamada A. Honda and Y. Mori Tetrahedron Lett. 1985 26 5787. 402 M. A. Ciufolini and S. Zhu J. Org. Chem. 1998 63 1668. 403 K. Watanabe K. Iguchi and K. Fujimori Heterocycles 1998 49 269. 404 M. Kuramoto K. Hayashi K. Yamaguchi M. Yada T. Tsuji and D. Uemura Bull. Chem. Soc. Jpn. 1998 71 771. 405 A. H. Daranos J. J. Fernández J. A. Gavín and M. Norte Tetrahedron 1998 54 7891. 406 S. Inoue S. Sugiura H. Kakoi K. Hashizumi T. Goto and H. Iio Chem. Lett. 1975 141. 407 H. Kakoi and S. Inoue Heterocycles 1998 48 1669. 408 A. D. Rodríguez A. Boulanger J. R. Martínez and S. D. Huang J. Nat. Prod. 1998 61 451. 409 P. L. Richardson A. D. Rodríguez A. Boulanger and S. D. Huang Acta Crystallogr. Sect. C 1998 54 66.410 M. Aknin A. Rudi Y. Kashman and E. M. Gaydou J. Nat. Prod. 1998 61 1286. 411 D. L. Martins and R. de A. Epifanio J. Braz. Chem. Soc. 1998 9 586. 412 L. A. Morris M. Jaspars K. Adamson S. Woods and H. M. Wallace Tetrahedron 1998 54 12953. 413 E. Ayanoglu T. Gebreyesus C. M. Beechan C. Djerassi and M. Kaisin Tetrahedron Lett. 1978 19 1671. 414 V. Singh S. Prathap and M. Porinchu J. Org. Chem. 1998 63 4011. 415 E. Ayanoglu T. Gebreyesus C. M. Beechan and C. Djerassi Tetrahedron 1979 35 1035. 416 J. M. MacDougal V. J. Santora S. K. Verma P. Turnbull C. R. Hernandez and H. W. Moore J. Org. Chem. 1998 63 6905. 417 P. S. Paramaswaran C. G. Naik S. Y. Kamat M. S. Puar P. Das and V. R. Hegde J. Nat. Prod. 1998 61 832. 418 A. Rudi T. L.-A.Dayan M. Aknin E. M. Gaydou and Y. Kashman J. Nat. Prod. 1998 61 872. 419 F. J. McEnroe and W. Fenical Tetrahedron 1978 34 1661. 420 G. M. König and A. D. Wright J. Nat. Prod. 1998 61 494. 421 A. S. R. Anjaneyulu N. S. K. Rao and K. S. Sagar Indian J. Chem. Sect. B 1998 37 267. 422 C.-Y. Duh S.-W. Wang H.-K. Tseng J.-H. Sheu and M. Y. Chiang J. Nat. Prod. 1998 61 844. 423 A. D. Rodríguez and A. L. Acosta J. Nat. Prod. 1998 61 40. 424 C.-Y. Duh S.-W. Wang H.-K. Tseng and J.-H. Sheu Tetrahedron Lett. 1998 39 7121. 425 A. M. Sulcimenova Khim. Prir. Soedin. 1988 4 535. 426 Y. Xing W. Cen Y. Li and Y. Li Chin. Sci. Bull. 1998 43 1403. 427 G. F. Matthée G. M. König and A. D. Wright J. Nat. Prod. 1998 61 237. 428 R. A. Endrada P. Proksch V. Wray L.Witte and L. van Ofwegen J. Nat. Prod. 1998 61 358. 429 J. Shin and W. Fenical J. Org. Chem. 1991 56 3153. 430 H. Kosugi O. Yamabe and M. Kato J. Chem. Soc. Perkin Trans. 1 1998 217. 431 M. Zhang and Z. Huang J. Nat. Prod. 1998 61 1300. 432 T. Iwagawa J. Kawasaki and T. Hase J. Nat. Prod. 1998 61 1513. 433 J. C. Coll P. S. Kearns and J. A. Rideout J. Nat. Prod. 1998 61 835. 434 A. D. Rodríguez J.-G. Shi and S. D. Huang J. Org. Chem. 1998 63 4425. 435 A. D. Rodríguez and J.-G. Shi J. Org. Chem. 1998 63 420. 436 S. A. Look M. T. Burch W. Fenical Q.-T. Zheng and J. Clardy J. Org. Chem. 1985 50 5741. 437 J. A. Marshall and J. Liao J. Org. Chem. 1998 63 5962. 438 A. D. Rodríguez and J. J. Soto J. Nat. Prod. 1998 61 401. 439 A. S. R.Anjaneyulu M. J. R. V. Venugopal P. Sarada G. V. Rao J. Clardy and E. Lobkovsky Tetrahedron Lett. 1998 39 135. 440 A. S. R. Anjaneyulu M. J. R. V. Venugopal P. Sarada J. Clardy and E. Lobkovsky Tetrahedron Lett. 1998 39 139. 441 A. S. R. Anjaneyulu P. M. Gowri and M. V. R. K. Murthy Indian J. Chem. Sect. B 1998 38 1090. 442 P. Ramesh N. S. Reddy Y. Venkateswarlu M. V. R. Reddy and D. J. Faulkner Tetrahedron Lett. 1998 39 8217. 443 M. Sugano T. Shindo A. Sato Y. Iijima T. Oshima H. Kuwano and T. Hata J. Org. Chem. 1990 55 5803. 444 J. Aigner E. Gössinger H. Kählig G. Menz and K. Pflugseder Angew. Chem. Int. Ed. 1998 37 2226. 445 A. D. Rodríguez E. González and S. D. Huang J. Org. Chem. 1998 63 7083. 446 A. D. Rodríguez A. L. Acosta and H. Dhasmana J.Nat. Prod. 1993 56 1843. 447 S. A. Look and W. Fenical J. Org. Chem. 1982 47 4129. 448 E. J. Corey and R. S. Kania Tetrahedron Lett. 1998 39 741. 449 K. Mori K. Iguchi N. Yamada Y. Yamada and Y. Inouye Chem. Pharm. Bull. 1988 36 2840. 450 H. Miyaoka Y. Isaji Y. Kajiwara I. Kunimune and Y. Yamada Tetrahedron Lett. 1998 39 6503. 451 J. Tanaka N. Ogawa J. Liang T. Higa and D. G. Gravalos Tetrahedron 1993 49 811. 452 T. Geller H.-G. Schmalz and J. W. Bats Tetrahedron Lett. 1998 39 1537. 453 T. Geller J. Jakupovic and H.-G. Schmalz Tetrahedron Lett. 1998 39 1541. 454 T. Lindel P. R. Jensen W. Fenical B. H. Long A. M. Casazza J. Carboni and C. R. Fairchild J. Am. Chem. Soc. 1997 119 8744. 455 S. Ketzinel A. Rudi M. Schleyer Y. Benayahu and Y.Kasman J. Nat. Prod. 1996 59 873. 456 M. D’Ambrosio A. Guerriero and F. Pietra Helv. Chim. Acta 1987 70 2019. 457 X.-T. Chen C. E. Gutteridge S. K. Bhattacharya B. Zhou T. R. R. Pettus T. Hascall and S. J. Danishefsky Angew. Chem. Int. Ed. 1998 37 185. 458 X.-T. Chen B. Zhou S. K. Bhattacharya C. E. Gutteridge T. R. R. Pettus and S. J. Danishefsky Angew. Chem. Int. Ed. 1998 37 789. 459 K. C. Nicolaou S. Kim J. Pfefferkorn J. Xu T. Ohshima S. Hosokawa D. Vourloumis and T. Li Angew. Chem. Int. Ed. 1998 37 1418. 460 K. C. Nicolaou J. Y. Xu S. Kim J. Pfefferkorn T. Ohshima D. Vourloumis and S. Hosokawa J. Am. Chem. Soc. 1998 120 8661. 461 K. C. Nicolaou T. Ohshima S. Hosokawa F. L. van Delft D. Vourloumis J. Y. Xu J. Pfefferkorn and S.Kim J. Am. Chem. Soc. 462 J. Rodríguez R. M. Nieto and C. Jiménez J. Nat. Prod. 1998 61 463 T. Iwagawa N. Takenoshita H. Okamura M. Nakatani M. Doye K. 464 J.-H. Sheu P.-J. Sung M.-C. Cheng H.-Y. Liu L.-S. Fang C.-Y. Duh 465 C. Subrahmanyam R. Kulatheeswaran and R. S. Ward J. Nat. Prod. 466 S. A. Look W. Fenical D. van Engen and J. Clardy J. Am. Chem. Soc. 467 D. Banjoo A. R. Maxwell B. S. Mootoo A. J. Lough S. McLean and 468 A. Fontana M. L. Ciavatta and G. Cimino J. Org. Chem. 1998 63 469 R. Koljak A. Lopp T. Pehk K. Varvas A.-M. Müürisepp I. Järving 470 C.-Y. Duh S.-K. Wang M.-J. Chu and J.-H. Sheu J. Nat. Prod. 1998 471 R. de A. Epifanio L. F. Maia A. C. Pinto I. Hardt and W. Fenical J. 472 Y. Seo K. W. Cho H. Chung H.-S. Lee and J. Shin J.Nat. Prod. 1998 120 8674. 313. Shibata and M. Shiro Heterocycles 1998 48 123. and M. Y. Chiang J. Nat. Prod. 1998 61 602. 1998 61 1120. 1984 106 5026. W. F. Reynolds Tetrahedron Lett. 1998 39 1469. 2845. and N. Samel Tetrahedron 1998 54 179. 61 1022. Braz. Chem. Soc. 1998 9 187. 1998 61 1441. 473 Y. Seo J. Shin and J.-I. Song J. Nat. Prod. 1995 58 1291. 474 N. Fusetani H. Nagata H. Hirota and T. Tsuyuki Tetrahedron Lett. 475 G. Della Sala I. Izzo F. De Riccardis and G. Sodano Tetrahedron 476 A. D. Rodríguez J. Rivera and A. Boulanger Tetrahedron Lett. 1998 477 L. A. Morris E. M. Christie M. Jaspars and L. P. van Ofwegen J. Nat. 478 M. Ankin V. Costantino A. Mangoni E. Fattorusso and E. M. 1989 30 7079. Lett. 1998 39 4741.39 7645. Prod. 1998 61 538. Gaydou Steroids 1998 63 575. 479 B. D. Morris and M. R. Prinsep J. Org. Chem. 1998 63 9545. 480 H. Lin Y. Yi W. Li X. Yao and H. Wu Chin. J. Mar. Drugs 1998 17 1. 481 G. R. Pettit C. L. Herald Y. Kamano D. Gust and R. Aoyagi J. Nat. Prod. 1983 46 528. 482 D. A. Evans P. H. Carter E. M. Carreira J. A. Prunet A. B. Charette and M. Lautens Angew. Chem. Int. Ed. 1998 37 2354. 483 P. A. Wender J. De Brabander P. G. Harran J.-M. Jimenez M. F. T. Koehler B. Lippa C.-M. Park and M. Siozaki J. Am. Chem. Soc. 484 P. A. Wender J. De Brabander P. G. Harran K. W. Hinkle B. Lippa 485 K. Suenaga T. Shibata N. Takada H. Kigoshi and K. Yamada J. Nat. 486 G. R. Pettit J.-P. Xu F. Hogan and R. L. Cerny Heterocycles 1998 487 C.R. Kaiser L. F. Pitombo and A. C. Pinto Spectrosc. Lett. 1998 31 1998 120 4534. and G. R. Pettit Tetrahedron Lett. 1998 39 8625. Prod. 1998 61 515. 47 491. 573. 53 Nat. Prod. Rep. 2000 17 7–55 488 T. Kusumi H. Uchida Y. Inouye M. Ishitsuka H. Yamamoto and H. Kakisawa J. Org. Chem. 1987 52 4597. 489 M. E. Jung B. T. Fahr and D. C. D’Amico J. Org. Chem. 1998 63 2982. 490 E. I. Graziani and R. J. Andersen J. Nat. Prod. 1998 61 285. 491 A. Spinella L. A. Alvarez and G. Cimino Tetrahedron Lett. 1998 39 2005. 492 G. Cimino A. Passeggio G. Sodano A. Spinella and G. Villani Experientia 1991 47 61. 493 A. Spinella L. A. Alvarez A. Passeggio and G. Cimino Tetrahedron 1993 49 1307. 494 H. L. Sleeper and W. H. Fenical J. Am. Chem. Soc. 1977 99 2367.495 R. Alvarez and A. R. de Lera Tetrahedron Asymmetry 1998 9 3065. 496 R. Alvarez M. Herrero S. López and A. R. de Lera Tetrahedron 1998 54 6793. 497 J. A. Roesener and P. J. Scheuer J. Am. Chem. Soc. 1986 108 846. 498 J. Maddock G. Pattenden and P. G. Wright J. Comput. Aided Mol. De. 1993 7 573. 499 S. K. Chattopadhyay and G. Pattenden Tetrahedron Lett. 1998 39 6095. 500 J. E. Biskupiak and C. M. Ireland Tetrahedron Lett. 1983 24 3055. 501 A. A. Birkbeck and D. Enders Tetrahedron Lett. 1998 39 7823. 502 M. Ochi K. Kataoka S. Ariki C. Iwatsuki M. Kodama and Y. Fukuyama J. Nat. Prod. 1998 61 1043. 503 Y. Fukuyama C. Iwatsuki M. Kodama M. Ochi K. Kataoka and K. Shibata Tetrahedron 1998 54 10007. 504 Y. Nakao W. Y. Yoshida C.M. Szabo B. J. Baker and P. J. Scheuer J. Org. Chem. 1998 63 3272. 505 K. Iken C. Avila M. L. Ciavatta A. Fontana and G. Cimino Tetrahedron Lett. 1998 39 5635. 506 C. A. Gray M. T. Davies-Coleman and C. McQuaid Nat. Prod. Lett. 1998 12 47. 507 A. Fontana C. Muniaín and G. Cimino J. Nat. Prod. 1998 61 1027. 508 K. McPhail M. T. Davies-Coleman and P. Coetzee J. Nat. Prod. 1998 61 961. 509 J. Hellou J. E. Thompson and R. J. Andersen Tetrahedron 1982 38 1875. 510 A. K. Bannerjee J. A. Correa and M. Laya-Mimo J. Chem. Res. (S) 1998 710. 511 D. E. Williams and R. J. Andersen Can. J. Chem. 1987 65 2244. 512 A. Srikrishna and T. J. Reddy Tetrahedron 1998 54 8133. 513 M. Satake K. Ofuji H. Naoki K. J. James A. Furey T. McMahon J. Silke and T.Yasumoto J. Am. Chem. Soc. 1998 120 9967. 514 K. Sasaki J. L. C. Wright and T. Yasumoto J. Org. Chem. 1998 63 2475. 515 D. Uemura T. Chou T. Haino A. Nagatsu S. Fukuzawa S. Zheng and H. Chen J. Am. Chem. Soc. 1995 117 1155. 516 J. A. McCauley K. Nagasawa P. A. Lander S. G. Mischke M. A. Semones and Y. Kishi J. Am. Chem. Soc. 1998 120 7647. 517 P. Ciminiello E. Fattorusso M. Forino S. Magno R. Poletti and R. Viviani Tetrahedron Lett. 1998 39 8897. 518 K. Murata M. Satake H. Naoki H. F. Kaspar and T. Yasumoto Tetrahedron 1998 54 735. 519 R. Durán E. Zubía M. J. Ortega S. Naranjo and J. Salvá Tetrahedron 1998 54 14597. 520 T. C. McKee D. L. Galinis L. K. Pannell J. H. Cardellina II J. Laakso C. M. Ireland L. Murray R. J. Capon and M.R. Boyd J. Org. Chem. 1998 63 7805. 521 C. J. Smith R. L. Hettich J. Jompa A. Tahir M. V. Buchanan and C. M. Ireland J. Org. Chem. 1998 63 4147. 522 S. Miao and R. J. Andersen J. Org. Chem. 1991 56 6275. 523 J. Boukouvalas N. Lachance M. Ouellet and M. Trudeau Tetrahedron Lett. 1998 39 7665. 524 B. S. Davidson and C. M. Ireland J. Nat. Prod. 1990 53 1036. 525 R. Rossi F. Bellina M. Biagetti and L. Mannina Tetrahedron Lett. 1998 39 7799. 526 M. A. Expósito B. López R. Fernández M. Vázquez C. Debitus T. Iglesias C. Jiménez E. Quiñoá and R. Riguera Tetrahedron 1998 54 7539. 527 A. Rudi M. Aknin E. M. Gaydou and Y. Kashman Tetrahedron 1998 54 13203. 528 S. G. Toske and W. Fenical Tetrahedron Lett. 1995 36 8355. 529 C. D. J. Boden M. C. Norley and G.Pattenden Tetrahedron Lett. 1996 37 9111. 530 M. C. Norley and G. Pattenden Tetrahedron Lett. 1998 39 3087. Nat. Prod. Rep. 2000 17 7–55 54 531 X. Fu T. Do F. J. Schmitz V. Andrusevich and M. H. Engel J. Nat. Prod. 1998 61 1547. 532 H. Sato M. Tsuda K. Watanabe and J. Kobayashi Tetrahedron 1998 54 8687. 533 R. G. S. Berlinck R. Britton E. Piers L. Lim M. Roberge R. M. da Rocha and R. J. Andersen J. Org. Chem. 1998 63 9850. 534 H. C. Vervoort S. E. Richards-Gross W. Fenical A. Y. Lee and J. Clardy J. Org. Chem. 1997 62 1486. 535 T. V. Hughes and M. P. Cava Tetrahedron Lett. 1998 39 9629. 536 A. Loukaci M. Guyot A. Chiaroni and C. Riche J. Nat. Prod. 1998 61 519. 537 L. H. Franco E. B. de K. Joffé L. Puricelli M. Tatian A. M. Seldes and J.A. Palermo J. Nat. Prod. 1998 61 1130. 538 R. A. Davis A. R. Carroll and R. J. Quinn J. Nat. Prod. 1998 61 959. 539 J. Kobayashi H. Nakamura Y. Ohizumi and Y. Hirata Tetrahedron Lett. 1986 27 1191. 540 Y. Murakami T. Watanabe H. Takahashi H. Yokoo Y. Nakazawa M. Koshimizu N. Adachi M. Kurati T. Yoshino T. Inagaki M. Ohishi M. Watanabe M. Tani and Y. Yokoyama Tetrahedron 1998 54 45. 541 M. Chbani M. Païs J.-M. Delauneux and C. Debitus J. Nat. Prod. 1993 56 99. 542 B. E. A. Burm M. M. Meijler J. Korver M. J. Wanner and G.-J. Koomen Tetrahedron 1998 54 6135. 543 B. R. Copp J. Jompa A. Tahir and C. M. Ireland J. Org. Chem. 1998 63 8024. 544 G. Koren-Goldschlager M. Aknin E. M. Gaydou and Y. Kashman J. Org. Chem. 1998 63 4601.545 A. Plubrukarn and B. S. Davidson J. Org. Chem. 1998 63 1657. 546 F. J. Schmitz F. S. de Guzman M. B. Hossain and D. van der Helm J. Org. Chem. 1991 56 804. 547 N. Bontemps I. Bonnard B. Banaigs G. Combaut and C. Francisco Tetrahedron Lett. 1994 35 7023. 548 Y. Kitahara F. Tamura M. Nishimura and A. Kubo Tetrahedron 1998 54 8421. 549 J. Kim E. O. Pordesimo S. I. Toth F. J. Schmitz and I. van Altena J. Nat. Prod. 1993 56 1813. 550 S. Nakahara J. Matsui and A. Kubo Tetrahedron Lett. 1998 39 5521. 551 B. S. Lindsay C. N. Battershill and B. R. Copp J. Nat. Prod. 1998 61 857. 552 H. Kang and W. Fenical Tetrahedron Lett. 1997 38 941. 553 T. Itaya Y. Hozumi T. Kanai and T. Ohta Tetrahedron Lett. 1998 39 4695. 554 A. Rueda E. Zubía M. J.Ortega and J. Salvá Nat. Prod. Lett. 1998 11 127. 555 L. A. Lenis M. J. Ferriero C. Debitus C. Jiménez E. Quiñoá and R. Riguera Tetrahedron 1998 54 5385. 556 K. Yamada E. Hara T. Miyamoto R. Higuchi R. Isobe and S. Honda Eur. J. Org. Chem. 1998 371. 557 K. Yamada Y. Harada Y. Nagaregawa T. Miyamoto R. Isobe and R. Higuchi Eur. J. Org. Chem. 1998 2519. 558 M. S. Maier A. Kuriss and A. M. Seldes Lipids 1998 33 825. 559 M. Inagaki R. Isobe Y. Kawano T. Miyamoto T. Komori and R. Higuchi Eur. J. Org. Chem. 1998 129. 560 Y. Kawano R. Higuchi R. Isobe and T. Komori Liebigs Ann. Chem. 1988 19. 561 R. Higuchi M. Kagoshima and T. Komori Liebigs Ann. Chem. 1990 659. 562 N. Chida N. Sakata K. Murai T. Tobe T. Nagase and S. Ogawa Bull. Chem. Soc.Jpn. 1998 71 259. 563 S. V. A. S. P. Kumar N. Dhananjaya and G. B. S. Reddy J. Chem. Res. (S) 1998 404. 564 A. J. Roccatagliata M. S. Maier and A. M. Seldes J. Nat. Prod. 1998 61 370. 565 E. V. Levina P. V. Andriyaschenko A. I. Kalinovsky and V. A. Stonik J. Nat. Prod. 1998 61 1423. 566 A. A. Kicha A. I. Kalinovskii N. V. Ivanchina and V. A. Stonik Russ. Chem. Bull. 1998 47 2032. 567 M. Iorizzi S. De Marino L. Minale F. Zollo V. Le Burt and C. Roussakis Tetrahedron 1996 52 10997. 568 I. Izzo F. De Riccardis and G. Sodano J. Org. Chem. 1998 63 4438. 569 S. De Marino M. Iorizzi E. Palagiano F. Zollo and C. Roussakis J. Nat. Prod. 1998 61 1319. 570 S. A. Avilov O. A. Drozdova V. I. Kalinin A. I. Kalinovsky V. A. Stonik E. A. Gudimova R.Riguera and C. Jiménez Can. J. Chem. 1998 76 137. 571 A. S. R. Anjaneyulu M .J. R. V. Venugopal L. Minale M. Iorizzi and E. Palagiano Indian J. Chem. Sect. B 1998 37 262. 572 A. Togi K. Kamino K. Adachi and Y. Shizuri Tetrahedron Lett. 1998 39 2775. 573 A. Togi K. Kamino K. Adachi and Y. Shizuri Tetrahedron 1998 54 15581. 574 N. Watanabe S. Watanabe J. Ide Y. Watanabe K. Sakata and K. Okamoto J. Mar. Biotechnol. 1998 6 11. 575 E. Zeeck T. Harder and M. Beckmann J. Chem. Ecol. 1998 24 13. 576 G. R. Pettit R. Tan J. Xu Y. Ichihara M. D. Williams and M. R. Boyd J. Nat. Prod. 1998 61 955. 577 G. R. Pettit M. Inoue Y. Kamano D. L. Herald C. Arm C. Dufresne N. D. Christie J. M. Schmidt D. L. Doubek and T. S. Krupa J. Am. 578 T. G. LaCour C. Guo S.Bhandaru M. R. Boyd and P. L. Fuchs J. Am. Chem. Soc. 1988 110 2006. Chem. Soc. 1998 120 692. 579 M. Satake M. Fukui A.-M. Legrand P. Cruchet and T. Yasumoto Tetrahedron Lett. 1998 39 1197. 580 R. J. Lewis J.-P. Vernoux and I. M. Brereton J. Am. Chem. Soc. 1998 120 5914. 581 H. Ishida H. Nakayasu H. Miyamoto H. Nukaya and K. Tsuji Chem. Pharm. Bull. 1998 46 12. 582 H. Okuni K. Tachibana N. Fusetani Tetrahedron Lett. 1993 34 5609. 583 H. Onuki K. Ito Y. Kobayashi N. Matsumori K. Tachibana and N. Fusetani J. Org. Chem. 1998 63 3925. 584 K. S. Moore S. Wehrli H. Roder M. Rogers J. N. Forrest Jr. D. McCrimmon and M. Zasloff Proc. Natl. Acad. Sci. USA 1993 90 1354. 585 X. Zhang M. N. Rao S. R. Jones B. Shao P. Feibush M. McGuiga N.Tzodikov B. Feibush I. Sharkansky B. Snyder L. M. Mallis A. Sarkahian S. Wilder J. E. Turse W. A. Kinney H. J. Kjærsgaard and R. S. Michalak J. Org. Chem. 1998 63 8599. 586 L. Zaman O. Arakawa A. Shimosu Y. Shida and Y. Onoue Toxicon 1998 36 627. Review a809395d 55 Nat. Prod. Rep. 2000 17 7–55

ISSN:0265-0568    

DOI:10.1039/a809395d

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Amaryllidaceae muscarine imidazole oxazole thiazole and peptide alkaloids and other miscellaneous alkaloids John R. Lewis Department of Chemistry University of Aberdeen Meston Walk Old Aberdeen UK AB24 3UE Received (in Cambridge UK) 20th August 1999 Covering July 1997 to June 1998 Previous review 1999 16 389 1 Introduction 2 Amaryllidaceae alkaloids 3 Muscarine imidazole oxazole and thiazole alkaloids 4 Peptide alkaloids 5 Miscellaneous alkaloids 6 References 1 Introduction This article now contains a section on amaryllidaceae alkaloids. In recent years the paucity of information on this alkaloid group suggested that it did not warrant a chapter in its own right. Even so there are annual fluctuations as to the quantity and the quality of publications of this alkaloid family.The remaining groups of alkaloids reviewed herein namely muscarine imidazole oxazole and thiazole alkaloids are grouped into the second section while peptide alkaloids continue to require their own section. Needless to say some overlap occurs in this section as the amide grouping is sometimes only a minor functionality compared to a more significant nitrogen–heteroatom arrangement where consequently classification requires it to be elsewhere in this review. 2 Amaryllidaceae alkaloids A comprehensive review on amaryllidaceae alkaloids has appeared in the 1998 edition of ‘Alkaloids’ vol. 51 by O. Hoshino it contains two hundred and three references to their biological sources and their synthesis.1 Galanthamine 1 continues to dominate the literature mostly in investigations into the search for better sources either in tissue culture or in new Narcissus cultivars and in synthesis.Four Narcissus cultivars have been evaluated for galanthamine production. The investigation showed that planting depth density bulb size or flower bud removal did not effect the galanthamine 1 content.2 It is now possible to evaluate the quantities of galanthamine 1 and related alkaloids in wild plants Dr Lewis graduated at University College Swansea; was Fulbright Fellow in 1958 at University of Iowa Ames later becoming Senior Lecturer in Organic Chemistry at Aberdeen University. He is now retired. This journal is © The Royal Society of Chemistry 2000 or tissue cultures of Narcissus confusus using HPLC.An isocratic system employing water–acetonitrile as mobile phase supplemented with octanesulfonic acid enabled alcoholic extracts of wild Narcissus confusus bulbs leaves scapes roots and flowers to be analysed while the buds from in vitro cultures were also included in the survey.3 Narcissus confusus cultures have been examined for their galanthamine 1 content. When grown with different amounts of sucrose the alkaloid content varied with sugar concentration (8–18% w/v) optimising after fourteen days growth in a sugar concentration of 9%.4 As reported in earlier reviews on amaryllidaceae alkaloids5,6 several syntheses of chiral (2)-galanthamine 1 depend upon the synthesis of its precursor (2)-narwedine 2.Recently two syntheses have been reported for the conversion of 3,4-dimethoxybenzaldehyde into (2)-galanthamine 1 one in kilogram quantities. Basically using the same steps the first report7 57 Nat. Prod. Rep. 2000 17 57–84 coupling steps only gave a less than 2% yield. Surely this step will be even further improved in the near future. A resolution of racemic narwedine type compounds has been achieved through formation of a salt of the alkaloid with a chirally enriched organic acid e.g. di-p-toluoyl-d-tartaric acid. Thus (+)-narwedine 2 gave predominantly the (2)-narwedine salt in 83% yield which upon reduction with l-selectride gave a 73% yield of (2)-galanthamine 1. The method is applicable to numerous narwedine derivatives.9 Brunsvigia littoralis bulbs have been shown to contain four alkaloids.10 They were identified as lycorine 6 1,2-di-Oacetyllycorine 7 ambelline 8 and crinine 9.Two studies on the constituents of Crinum latifolium have reported that the leaves contain a new alkaloid 6-hydroxycrinamidine 10,11 while the dried powdered bulbs obtained also from Crinum latifolium12 have been shown to contain two pyrrolophenanthridine alkaloids namely lycorine 6 and pratosine 11. In another study13 on this plant the rhizomes have been shown to contain lycorine 6 and 3a-1,2-didehydroxycrinan- 3-ol 12. The leaves of Crinan oliganthum native to Cuba has been studied phytochemically and a new alkaloid isolated.14 Called cribetamine its structure was determined by spectroscopic measurements and comparisons with nerbowdin 13.A second report15 on this plant describes a new alkaloid called crinatine 14. It is also a member of the crinidine group of alkaloids. The recognition that cripowelline 1 14 and cripowelline 2 15 have anti-insect repellent properties has led to their being patented.16 Both these naturally occurring alkaloids were obtained from Crinum powellii. The alkaloids have also been reported in detail with the bulbs being identified as a good source for them.17 describes the half molar quantity preparation of 6-bromoisovanillin in a one-pot procedure. The oxidative cyclisation which was carried out on 4 used potassium ferricyanide in toluene– aqueous sodium bicarbonate and gave yields of ~ 30% of (+)-bromonarwedine 3.Debromination and resolution gave an overall yield of about 19% of (2)-galanthamine 1. In the second method8 a tonne quantity of 6-bromoisovanillin was produced and twelve kilogram quantities employed in the oxidative coupling step now using 5 led to an efficient conversion into (+)-bromonarwedine 3 and thence to (2)-galanthamine 1. The quantity production of this alkaloid can be seen as one of the highlights of organic chemistry since originally the oxidative Lycorine 6 has been isolated from the leaves of the tropical plant Eucharis grandiflora.18 Nat. Prod. Rep. 2000 17 57–84 58 Hymenocallis cayamansis seeds have been shown to contain four members of the tazettine group of alkaloids.19 They are marconine 16 tazettine 17 criwelline 18 and pretazattine 19.An extraction of the plant Narcissus asturiensis has shown20 that it contains hemanthamine 20 hemanthidine 21 tazettine 17 and epimacronine 22. An X-ray crystallographic study of the alkaloid ismine obtained from Narcissus asturiensis and crystallised from n-hexane–chloroform shows that it has two non-equivalent molecules in the asymmetric unit 23 through intermolecular hydrogen bonding involving the hydroxy groups.21 Pancratium foetidum has been examined for its alkaloid content and trispheradine 24 crinamine 25 haemanthidine 21 lycorine 6 and crinine 9 were found to be present.22 Many of the amaryllidaceae alkaloids are biosynthetically created by a phenol activated oxidative coupling reaction. In the laboratory a large number of oxidising agents have been successful in emulating nature.One of merit is the relatively non-toxic phenyliodine(iii) bis(trifluoroacetate) (PIFA). This hypervalent iodine reagent in poorly nucleophilic polar solvents can induce ortho–para and para–para coupling. Thus beladine derivative 26 cyclised intramolecularly to give 27 in 61% yield at 240 °C in five minutes.23 A variant in intramolecular ring closures is the dehydrobromination of phenylamine 28 by palladium acetate to give crinasiadine 29. If a palladium chloride catalyst was used triphaeridine 30 resulted.24 A rather well thought out procedure for the synthesis of (+)-narciclasine 33 involves a cyclisation of amide 31 which incorporated an epoxide grouping as a synthon for the 3,4-dihydroxy functions.This together with a hydrogen bonded carbonyl group so as to exert conformational control promoted photocyclisation. A 43% conversion to the tricyclic trans-fused phenanthridone also produced only a single diastereoisomer 32. Further manipulation resulted in (+)-narciclasine 33 in 37% overall yield.25 Pancratistatin 36 and related alkaloids such as narciclasine lycoricidine and its 7-deoxy-derivative all possess excellent antitumour properties. A new synthesis of (+)-pancratistatin 36 employs an intramolecular electrophilic aromatic substitution procedure resulting in ether 34 being converted into a diastereomeric mixture 35 upon treatment with Tf2O in base.26 Further manipulation most of which has already been published, 27 gave the natural product.Benzo[c]phenanthridine alkaloid chelerythrine 39 is also synthesised by an intramolecular ring closing reaction involving an amide. In this case 6-halo-2,3-dimethoxy-N-methyl-N-(6,7-methylenedioxy- 1-naphthyl)benzamide 37 upon treatment with Heck reagent palladium(iii) acetate with ligand POT in DMF under reflux gave oxychelerythrine 38 in < 90% yield. A small improvement in yield was achieved with the iodo-precursor rather than using the bromo-amide. Reductive deoxygenation gave chelerythrine 39.28 An intramolecular concerted pericyclic allenesilane imino ene cycloaddition is the key step in the synthesis of the 5,11-methanomorphanthridine alkaloids (2)-montanine 44 (2)-coccinine 45 and (2)-pancracine 46. Thus 40 prepared from 41 and 42 by heating in mesitylene at 50 °C followed by TBAF treatment at 0 °C and deprotection enabled reduction to ene 43 which could be converted into natural products 44 45 and 46.29,30 Tetracyclic tazettine 17 has been synthesised in sixteen steps and in 11% yield.31 Several synthetic steps deserve mention in the creation of the stereochemistry required for this alkaloid.Firstly acyl azide 47 reacted with an excess of Warkentin oxadiazoline 48 to give 49. Acid hydrolysis of the acetal gave a 59 Nat. Prod. Rep. 2000 17 57–84 cyclic alcohol which after acid treatment and methylation gave enone 50. Samarium iodide HMPA–NaBH4 reduction gave the trans fused product 51 which on reintroduction of the double bond affording 52 and manipulation of ring A via 53 gave racemic tazettine 17 It appears that tazettine is not a natural product but an artefact derived from pretazettine 19 during work up.Pavine alkaloid thalimonine 55 has been synthesised by an acid-mediated cyclisation of the 1,2-dihydroisoquinoline 54. The resulting racemic mixture being resolved to give the natural (2)-enantiomer.32 3 Muscarine imidazole oxazole and thiazole alkaloids A facile synthesis of (2)-allomuscarine 58 has been reported33 which starts from easily obtainable 1-dimethylamino-1,3,6-trideoxyhexitol 56 whereby HF treatment gives the 2,5-anhydride 57 that upon methylation produces (2)-allomuscarine 58. In principle (+)-allomuscarine could be synthesised utilising the enantiomer of 56.A number of marine sponge metabolites contain the imidazole ring system and frequently it is substituted in the two position by an amino-grouping. It has now been established that NCS oxidation of 59 in methanol gives the trans adduct 60 predominantly (99%). Thermal elimination of methanol gives diene 61 which can be acylated with brominated pyrrole carboxylic acids to give a variety of natural products.34 Employing a Stille coupling procedure it has been found that the protected bromoindolylmaleimide 62 reacts with 5-tributylstannyl-1-methyl-1H-imidazole to give 63 which was subsequently converted into didemnimide C 64. Irradiation of 63 with a halogen lamp in the presence of iodine gave pentacyclic 65 and it is thought that these cyclodidemnimides will soon be found as natural products.35 A Streptomyces species isolated from a soil sample has been found to produce a novel amino acid.36 Designated TU-185 it has an imidazole-ornithine structure 66.Nat. Prod. Rep. 2000 17 57–84 60 (2)-Phenylahistin 67 is a new type of mammalian cell cycle inhibitor obtained as a racemic mixture from the fungus Aspergillus ustus.37 Separation of the enantiomeric mixture by HPLC gave the S-enantiomer which was active but the R-isomer was not. In a series of Caribbean sponges belonging to the Agelas family all four namely Agelas clathrodes Agelas conifera Agelas dispar and Agelas longissima contained a number of known bromopyrrolo imidazole alkaloids interestingly they all contained the novel alkaloid dispacamide C 68.38 Taurocidin A and taurocidin B are bioactive constituents of a marine sponge of the Hymeniacidon family.Their structures were elucidated by spectroscopic measurements and they have both been shown to have a taurine residue attached to the 2-amino-imidazole ring i.e. 69 and 70.39 A synthesis of the marine imidazole alkaloids croidine 72 clathrodine 73 and hymenidine 74 has established a general synthetic route to imidazole alkaloids starting with the ‘trans’ propene amine 71 whereby condensation with the appropriate brominated pyrrole-2-carboxylic acid led to each of the natural products. A synthesis of the ‘cis’ propene amine 75 ultimately led to the first formal synthesis of keramadin 76.40 2-Thiohydantoin 77 is the starting point for the first synthesis of the marine sponge natural product dispacamide 81.41 Its condensation with aldehyde 78 in the presence of piperidine afforded stereochemically (Z) pure alkylidene thiohydantoin 79.Regioselective S-methylation produced 80 and thence to dispacamide 81 by heating to 60 °C in a sealed tube with ammonia. Alternatively thiohydantoin 79 could be directly converted into 81 by treatment with tert-butyl hydroperoxide in aqueous ammonia at room temperature. A synthesis of polycarpine 83 the sulfur containing alkaloid found in the ascidian Polycarpa aurata has been achieved first through the synthesis of key intermediate 82. Reaction with Sethylthiourea in base followed by treatment with S2Cl2 in acetic acid gave polycarpine 83 as its dihydrochloride salt.42 The Micronesian sponge Leucetta cf chagosensis contains four new imidazole alkaloids as well as the known isonaamidine B 84.The new ones are isonaamine B 86 and isonaamidine D 85 together with the zinc complex of isonaamidine B 87 and a mixed zinc complex 88 containing both isonaamidine B and isonaamidine D.43 Pyronaamidine 9-(N-methylimine) 89 is a new imidazole alkaloid isolated from a sponge of the Leucetta family. This coloured sponge was characterised as Leucetta sp cf chagosensis and was located in Micronesia near Rota Island. It is made up of small bright lemon coloured semispherical masses.44 A total synthesis of the imidazole alkaloid kealiiquinone 91 has resulted in a tautomeric compound 92 being prepared.45 This may be due to the penultimate step of oxidation of phenol 90 in the presence of salcomine and oxygen in acetonitrile giving preferentially 92.There is an equilibrium between 91 and 92 which depends upon the solvent. The synthesis of a number of sarcodictyins which includes the first total synthesis of sarcodictyin B 93 has allowed some structure–activity relation- 61 Nat. Prod. Rep. 2000 17 57–84 ships to be made of the antitumour activity of these marine natural products and to relate this to the eleutherobins.46 The antitumour active metabolite obtained from Streptomyces species NA 22598 has been identified as 94.47 The oxazoline ring system has been found in the secondary metabolite obtained from the culture broth of Actinomadura species MJ502-77F-8.Methyl 2-(2A-hydroxyphenyl)-4,5-dihydro-oxazole-4-carboxylate 95 was identified by spectroscopic methods and was reported to be an antibiotic.48 Two novel oxazole alkaloids have been isolated from two species of ladybirds.49 Both insects Epilachna varivestis and Epilachna borealis contain bicyclic alkaloids 96 and 98 together with their cogeners 97 and 99. Martefragin A 100 is a metabolite found in the red alga Martensia fragilis. Structure elucidation was achieved by spectroscopic measurements on its methyl ester.50 A total synthesis of rhizoxin D 109 employs a convergent enantiocontrolled procedure.51 The difficult macrolactonization steps 106 to 107 were circumvented by first assembling 106 through Wittig reaction of aldehyde 101 with bromodiene 102 which gave a mixture of epimeric alcohols which could be separated by flash chromotography to give the required epimer 103.Its enantiomer 104 could be recyclised to 103 by oxidation and reduction using (R)-2-methyl-CBS-oxazaborolidine. Extension to the ester 105 was followed by release of aldehyde 106 so that an intramolecular ring closure employing the Horner– Emmons procedure created macrocycle 107. Modification via deprotection and attachment of the oxazole terminus completed the synthesis (Scheme 1). Two papers52,53 describe approaches to the synthesis of rhizoxin 110 in convergent terms by dividing the molecule into two sections as indicated in structure 110 (wavy lines). The synthesis is yet to be completed.Verongida sponges Aplysina acrophoba and Aplysina cavernicota contain a number of modified tyrosine derivatives related to the bromotyrosines. Two new metabolites recently found are oxohomoaerothionin 111 and 11-hydroxyfistularin 112.54 The marine sponge Discodermia calx contains the bioactive marine metabolite dephosphonocalyculin A 113.55 Its absolute stereochemistry was determined by converting 113 and calyculin A56 into a common compound. A new antimicrobial and cytotoxic substance 16-methyloxazolomycin 114 has been obtained from a species of Streptomyces. 57 The Horner–Emmons procedure for intramolecular cyclisation through lactone formation has also been successfully applied58 in the synthesis of the antibiotic (2)-madumycin 115.The determination of the absolute configuration of natural products normally involves X-ray crystallographic measurements or chemical degradation. Using hennoxazole A 116 it has been shown that applying ab initio calculations it is possible to combine molar rotation angles for ‘molecular fragments’ of the parent molecule and so determine which stereochemical arrangement is correct. Thus fragments 117 118 and 119 gave the required data for hennoxazole A’s absolute stereochemistry. 59 A synthesis of (+)-nostocyclamide 120 has supported the stereochemical assignment as 2S,12R even though the optical rotation of the synthetic product is +51° while the natural product was +25°. The discrepancy is possibly due to the fact that only a small quantity of the natural product has been available.60 Scheme 1 Reagents i BuLi (2 equiv.) THF–Et2O–pentane (4+1+1); 2120 °C to 90 °C then 102 290 °C to 278 °C; ii TPAP NMO 4 Å sieves CH2Cl2; iii (R)-2-methyl-CBS-oxazaborolidine BH3 THF 210 °C; iv SEMCl iPrEtN CH2Cl2; v TBAF THF; vi diisopropylphosphonoacetic acid 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide methyl toluene-psulfonate DMAP 4 Å series CH2Cl2; vii HOAc–H2O (4+1) 48 h; viii NaIO4 THF–H2O; ix DBu (2 equiv.) CH3CN; LiCl (15 equiv.) 4.6 31024 M; x Horner–Emmons cyclization; DDQ H2O CH2Cl2; xi MnO2; xii KHMDS 4-(3-diphenylphosphinoyl)-2-(methylpropenyl)-2-methyloxazole; xiii Me Dolastin 1 121 is a cyclic hexapeptide isolated from the Japanese sea hare Dolabella auricularia and it has been identified by spectroscopic analysis.61 Its absolute stereochemistry came from its hydrolysis and identification of the chirality of the amino-acid components so released.Dolastin 18 122 has been isolated also from the sea-hare Dolabella auricularia but 2BBr THF–CH2Cl2 0 °C. Nat. Prod. Rep. 2000 17 57–84 62 by using a cancer cell growth inhibitor test62 so as to focus on the active constituent. (+)-Curacin A 123 is a relatively unstable molecule and consequently is unlikely to become a drug for cytotoxic purposes. Its mode of action through colchicine binding and consequently causing tubulin polymerisation inhibition has prompted several synthetic procedures. The latest63 offers yet another route to the natural product and its modification will lead to analogues.A series of bactericidal and antimycotic agents have been obtained from the culture broth of strain DSM10320 of Sorangium cellulosum.64 Two such metabolites are thuggacin A 124 and thuggacin B 125. The total synthesis of (2)-pateamine A 128 the novel immunosuppressive agent found in the Mycale sponge family has been reported.65 A novel feature involves the use of a blactam functionality so that its hydrolysis causes an intramolecular lactonisation to take place. Thus 126 upon treatment with 9 equiv. of Et4NCN in chloroform at room temperature gave a 68% yield of 127. Although epothilone A 129 and epothiline B 130 have been synthesised previously the newest approach employs solid state methodology. This enables a variety of analogues to be created and to be assessed66 for their effectiveness against taxol resistant cancer cell lines.Oriamide 131 is a cyclic peptide containing the unprecedented amino acid 4-propenoyl-2-tyrosylthiazole. This unusual thiazole containing alkaloid was obtained from a sponge of the Theonella family.67 In the convergent synthesis of (2)-mirabazole B 133 a linear tripeptide amide 132 which contains three S-benzyl-2-methylcysteine residues could be converted into the thiazoline/thiazole rings using titanium tetrachloride and thence to 133.68 A bioassay guided fractionation has led to the isolation of a new cyclic peptide preulithiacyclamide 134 from the ascidian Lissoclinium patella. It has a high macrophage scavenger receptor inhibitor property but it was not as active as ulithiacyclamide69 135 which was also present in the extract.70 Thiostrepton Sch40832 is a new minor component found in the antibiotic complex produced by Micromonospora carbonacea africana. This disaccharide containing sulfur rich metabolite 136 is an active Gram-positive bacteriostat.71 4 Peptide alkaloids A succinylanthranilic acid ester 137 has been obtained from the methanolic extract of the dark brown alga Jolyna laminarioides. This metabolite exhibited chymotrypsin inhibitory activity and some antifungal activity.72 Circinamide 138 is a novel and the first papain inhibitor to be isolated from the cyanobacterium Anabaena circinalis which was cultured on a CB medium under aerobic conditions and the freeze dried cells extracted with ether–water.Activity was 63 Nat. Prod. Rep. 2000 17 57–84 metabolites namely myxopyronin A 141 and myxopyronin B 142 differ only in one of the side chains and consequently a found in the aqueous layer and 138 was isolated as a bright yellow solid.73 A new ceramide 139 isolated from the epiphylic dinoflagellate Coolia monolis has an unusual side chain in that it is branched. This also gives rise to the recognition of a new type of fatty acid one with nineteen carbon atoms.74 Inhibitor activity in vitro is displayed by metabolite 140 isolated from a Fusarium mycotoxin both Gram-positive and Gram-negative bacteria being affected. Its synthesis was easily undertaken by the condensation of 5-ethoxyfuran-2(5H)-one with acetamide which occurred in hot concentrated hydrochloric acid to give the natural product.Synthetic analogues only showed minimal biological activity.75 Myxopyronins were the RNA polymerase inhibitors isolated from gliding bacteria in the early 1980’s. Two of these Nat. Prod. Rep. 2000 17 57–84 64 synthesis has been devised to introduce side chains onto a core pyrone. This procedure however resulted in racemic products. 76 Giganticine 143 is a novel nonprotein amino acid isolated from the root bark of Calotropis gigantea. It has some antifeedant properties as well as a variety of homeopathic applications.77 cis-p-Coumaroylaginatine 144 is a genuine leaf opening substance isolated from Albizzia julibrissin. As it easily opens the leaves of this plant it has stimulated the research for an unknown substance that causes its leaf closing.78 Nat.Prod. Rep. 2000 17 57–84 Radiosumin 149 is a trypsin inhibitor obtained from the fresh water blue–green alga Plectonema radiosum. Its synthesis79 was based primarily on the assumption that both amino-acid components possessed the same stereochemistry namely S at C- 7. Thus the synthesis of methyl 2-amino-3-(4-acetylaminocy- 65 clohex-2-en-1-ylidene)propionate 145 and of methyl 2-methoxyimino-3-(4-aminocyclohexylidene)propionic acid 146 protected respectively as the benzyloxycarbonyl group 147 and with the tert-butoxycarbonyl group 148 thus enabled condensation to be achieved with diethyl phosphorocyanidate [DEPC(EtO)2P(O)CN].Diastereoisomer separation gave 150 whereupon deprotection produced the natural product 149. Epoxyquinomicins A B C and D 154 are new antibiotics isolated from the fungal broth of an Amycolatopsis fungus. Their structures80 and biological properties81 have been described in some detail. Rufulamide 155 is an oligopeptide analogue isolated from the liverwort Metzgeria rufula. Its structure consists of two anthranilic acid units coupled through l-glutamic and malonic acids. Its synthesis was achieved by normal peptide procedures. 82 Korormicin 156 had been isolated from the marine bacterium Pseudoalteromonas species F-420 found on the surface of a species of a macroalga of the Halimeda family. It appears to exhibit antimicrobial activity against marine Gram-negative bacteria.83 Substance FA-70D 157 is produced by a Strepto- Nat.Prod. Rep. 2000 17 57–84 66 myces species called strain FA-70D. It has been reported and patented84 as useful for the treatment of osteoporosis due to its ability to inhibit specifically cathepsin proteases. Malyngamides M and N have been isolated from the Hawaiian red alga Gracilaria coronopifolia. This alga had been previously found to have been associated with an unusual food poisoning epidemic in Hawaii but these two new metabolites 158 and 159 are not thought to be the causative agents.85 The three gymnastatins namely A B and C are produced by a strain of the fungus Gymnascella dankaliensis obtained from the sponge Halichondria japonica.86 Structural modification occurs mainly in the six membered ring A is 160 B is 161 and C 162.A novel antibiotic has been produced by shake culture of species 2128 of a Penicillium fungus. Designated E-2128-1 163 shows an inhibitory effect on 1L-1 production.87 Andrimide (164) isolated from the natural bacterium Pseudomonas fluorescens has been found to be bacteriostatic towards Gram-(+) and Gram-(2) bacteria and preferentially inhibited RNA polymerase and UMP kinase activities.88 Microginin 299A and microginin 299B are metabolites produced by the cyanobacterium Microcystis aeruginosa which is a causative agent for bloom in fresh water lakes. Both these 4 dioxane reflux 20 h; vi 70% HClO4 Scheme 2 Reagents i (i) EtOH EtONa reflux 2 h then acrylonitrile H2O dioxane reflux 2.5 h; ii CH2N2 ether then NaBH4 CeCl3 MeOH 0 °C to rt 3 h then H+; iii (CH2OH)2 TsOH benzene reflux 8 h; iv LiAlH4 ether 0 °C 3 h; v 17% HClO dioxane reflux 20 h.colourless amorphous compounds 165 and 166 have leucine aminopeptidase inhibitor properties.89 A glutamate receptor antagonist called kaitecephalin 167 has been isolated from the fungus Eupenicillium shearii species PF 1191.90 Yunnanmycin antibiotics which are claimed to have low toxicity are produced by culturing Streptomyces species strain 2321.91 Typical is yunnanmycin 168 R = H but other antibiotics found in this culture fluid are its acid derivatives where R = H Na K NH2 Me or Et. Dipeptides TAN A B C and D are antibiotics successful in the treatment of methicillin resistant Strephylococcus aureus.92 These metabolites isolated from the bacterium Flexibacter species PK-72 and PK-176 have been synthesised and their structures thus confirmed.A and B are stereochemically related at C-5 (169) as are C and D at C-2 (170). Two cytotoxic macrolides found in the common Caribbean sea whip Eunicea succinea possess a salicyl grouping involved in a twelve membered ring 171. Structurally they are related by being geometric isomers at C-17. Salicylihalamide A is the Eisomer and salicylihalamide B is the Z-isomer. From an analysis of structures recorded on the NCI data base these metabolites represent a new class of cytotoxic agents.93 Celenamide E 172 is a tripeptide alkaloid obtained from the Patagonian sponge Cliona chilensis.An unusual feature structurally is its dehydro amino-acid moiety.94 Cherinonaine is a novel dimeric amide found in the stems of the plant Annona cherimola.95 It has a unique ether bridge between two monomeric amides 173. Amonabactin 174 is the name given to a family of novel siderophores isolated from a pathogenic bacterium. These iron chelating compounds found in Aeromonas hydrophilia are thought to be paramount in the organisms growth under low iron concentrations.96 Cymbimicin A 175 and cymbimicin B 176 possess novel cyclophilin binding behaviour; A being one hundred times more active than B; they were isolated from a strain of Micromonospora by a bioassay monitored separating procedure.97 67 Nat. Prod. Rep. 2000 17 57–84 The tunicate Aplidium lobatum contains two novel cytotoxic macrolides99 Lobatamide A 178 occurs with its isomer B.A mixture of antimycin A5 and A6 can now be produced in a shake culture of Streptomyces species POL-129. A6 179 is marginally in excess.100 Antifungal antibiotic UK-3A has the novel structure 180 although somewhat related structurally to Nat. Prod. Rep. 2000 17 57–84 68 The structural elucidation of YM-75518 an antibiotic isolated from Pseudomonas species Q 38009 was obtained by extensive NMR spectroscopy revealing the novel macrolide structure 177.98 2 Pd–C CH2Cl2–MeOH (90+10) rt 10 h; vii Scheme 3 Reagents i EDCl DMAP CH2Cl2 rt 4 h; ii O3 CH2Cl2 278 °C 0.5 h; iii H-Leu-OBut CH2Cl2 278 °C 1 h; iv AgNO3 THF– H2O (4+1) rt 24 h; v TFA–CH2Cl2 (1+1) rt 1.5 h then DPPA NaHCO3 DMF 215 °C 40 h; vi H 6-methylhept-2-enoic acid EDCl rt 3 h.antimycin A it is much weaker in activity. It was found in the mycelial cake of Streptomyces species 571-02.101 Another chaetoglobosin designated P 181 has been obtained from a fungus of the genus Discosia.102 dioxane to give cyanide 185. Protection of the diketone as its enol ether enabled reduction of one keto group which was dehydrated in situ to produce a,b-unsaturated ketone 186. Ketalization allowed reduction to amine 187 and thence to dienamine 188. A tandem Michael addition and intramolecular Hannich reaction between 188 and 189 gave the tetracyclic molecule 190 which could then be manipulated to create (+)-huperzine B 191 Scheme 2.105 Puberulin A 192 is a new diketopiperazine alkaloid isolated from the fungus Penicillium regulosum.106 Xylaria hypoxylon is a fungus isolated from soil containing decayed wood chips.On cultivation it produced six new cytochalasins.107 They are designated 19,20-epoxycytochalasin R 193 18-deoxy- 19,20-epoxycytochalasin R 194 18-deoxy-19,20-epoxycytochalasin Q 195 19,20-epoxycytochalasin N 196 19,20-epoxycytochalasin C 197 and 19,20-epoxycytochalasin D 198. Two known bengamides A and B together with five related new amino acid derivatives have been isolated from the marine sponge Jaspia carteri.108 Designated bengamides G H I J and K they are 199 200 201 202 while K is a relative of bengamide B having a shorter side chain 203. Four thirteen membered ring spermidine alkaloids have been synthesised using a common synthon namely the diazalactam 204.109 Addition of the appropriate acyl residue was introduced using the Mukaiyama procedure i.e.the carboxylic acid Nmethyl-2-chloropyridinium iodide in triethylamine–methylene chloride was stirred at room temperature prior to the addition of synthon 204. After several hours the reaction mixture was worked up to give the natural product (2)-(S)-celacinnine 205 (2)-(S)-celabenzine 206 or (2)-(S)-celafurine 207. Acetylation of (2)-(S)-celacinnine 205 gave its N-acetyl derivative namely (2)-(S)-viburnine 208. Using the established synthetic strategy for spermidine alkaloids reported in a previous review,110 the spermidine alkaloids (+)-(2S)-dihydromyricoidine 209 and (+)-(2S)-myricoidine 210 have been synthesised.111 Apochalasins are antibiotic metabolites produced by the fungus Aspergillus.A new species FO-4282 has been cultivated and it produced two new metabolites apochalasin F 211 and apochalasin G 212.112 A biamide with an unusual structure called bahamamide 213 has been isolated from an undescribed marine bacterium designated CNE-852.113 Antitumour metabolite FE 399 214 is produced by cultivating the filamentous fungus Ascochyla.114 The synthesis of eurystatin A 223 has been achieved using an acyl cyanophosphorane methodology first to produce the a,b-diketo-amide group necessary for its synthesis. Thus protected alanine 215 upon treatment with cyanophosphorane 216 gave 217 which on ozonolysis gave diketonitrile 218 which reacted in situ with leucine tert-butyl ester.Further peptide extension with ornithine gave 219. This was followed by deprotection of 219 and intramolecular cyclisation of this peptide 220 to give macrocycle 221 which on further deprotection gave amine 222 whereby 6-methylhept-2-enoic acid could be attached via EDCl mediation115 to give the natural product 223 (Scheme 3). A methanol extract of the seeds of Albizia lebbek contained three new macrocyclic alkaloids belonging to the budmuchiamine family. They are budmuchiamine L4 224 budmuchiamine L5 225 and budmuchiamine L6 226. Budmuchiamines A B C and D were also found in this extract.116 Verballoscenine 227 is the Z-isomer of verbascenine 228 and was found in the leaves of the plant Verbascum phoeniceum.117 Also present were the N-unacetylated analogues verbacine and verballocine.Using a new test procedure for identifying mitotic inhibitors it has been possible to isolate a new mammalian cell cycle inhibitor in the culture fluid of a Phoma species (SNF 1778). Compound 182 belongs to the cytochalasin group of natural products and is accompanied by its 6,7-deepoxy compound which is presumably its biogenetic precursor.103 Rubrobramide 183 is a cytotoxic and phytoxic metabolite found in the culture filtrate of Cladobotryum rubrobrunnesceus.104 The first total synthesis of huperzine-B 191 produced this Lycopodium alkaloid in racemic form. It took twelve steps with an overall 6.6% yield.Thus ketoester 184 via an intramolecular Dieckmann condensation added to acrylonitrile in refluxing Antitumour substances designated BE 42303 229 are manufactured with a Streptomyces species A42303. In all four metabolites A B C and D were isolated and the patent describes the synthesis of C and D from A and B respectively.118 A synthesis of both antitumour macrolides cryptophycin 1 233 and cryptophycin 8 234 has been described.119 The procedure is 69 Nat. Prod. Rep. 2000 17 57–84 70 Nat. Prod. Rep. 2000 17 57–84 efficient and enantiospecific and a particularly interesting feature is the creation of the epoxide grouping using reagent 4-azido-1,1,1-trimethoxybutane so as to give the ester 230 which was employed to stereospecifically create chloro-ester 231 which could then be hydrolysed under mild conditions so as to create chloro-alcohol 234 and thence cryptophycin D 233.Lebstatin 235 is a cell cycle inhibitor manufactured from Streptomyces hygroscopicus.120 An expeditious synthesis of geodiamolide A 236 has employed an efficient combination of tripeptide and polypropionate units using an Evans asymmetric alkylation the Mitsunobu esterification and the macrolactamization proceeded through use of di-phenylphosphorazidate.121 Cremimycin 237 is a novel nineteen membered macrocyclic lactam antibiotic isolated from a Sreptomyces strain.122 A total synthesis by solid phase methodology of oscillamide Y 239 has been reported.123 An aminomethyl polystyrene resin was used as the core and subsequently six amino acids were connected to give the protected open chain peptide precursor 238.Deprotection allowed cyclisation to be induced using PyBroP and DIPEA in DMF and the resulting cyclic peptide was cleaved from its core suport using weakly diluted trifluoroacetic acid. Since all four enantiomeric amino acids were used in this synthesis individually the natural products’ structure was confirmed as having l-N-methylalanine and lhomotyrosine incorporated in the metabolite. Cyclocinamide A 240 is an unusual cytotoxic halogenated hexapeptide isolated from the marine sponge Psammocinia. One of its unusual features is its tetrapeptide core.124 A total synthesis of (2)-mycotrienol 242 and (+)-mycotrenin-1 243 used as a penultimate step a tandem Stille coupling procedure to produce configurationally pure (E,E,E)triene 241 which could be oxidised with ceric nitrate to quinone and then to 242.If addition of the cyclohexylcarbonyl-d-alanine entity proceeded CAN oxidation it produced (+)-mycotrenin 1 243.125 The total synthesis of macbecin-1 245 was also obtained by elaboration of an aromatic carboxylic acid precursor 244 which was cyclised and oxidised to the quinone macbecin-1 245.126 A total synthesis of (+)-damavaricin D 246 a member of the streptovaricin group of antibiotic alkaloids also used the amide link as the macrolide forming step.127 Goniothalactam 247 is a new alkaloid found in the bark of Goniothalamus borneensis.128 In all twelve natural products were isolated in this investigation but the other eleven were nonalkaloidal.A novel cinnamide dimer 248 has been isolated as a minor component of the Indian Ocean soft coral Sinularia flexibilis. 129 More cyclopeptide alkaloids have been isolated from Scutia buxifolia found in South America. Scutianine K 249 and scutianine 250 have been characterised by spectroscopic analysis.130 71 Nat. Prod. Rep. 2000 17 57–84 Exumolides A and B are cyclic hexadepsipeptides possessing antimicrobial activity. Isolated from a species of the marine fungus Scytalidium they have been characterized as 251 and 252 respectively.131 A further examination of the sea hare Dolabella auricularia guided by bioassay has located another human cancer cell growth inhibitor called dolastin 16 it has structure 253.132 Dolastin 17 (254) isolated from the same species of sea hare is reported to have an unusual alkyne feature.It also exhibited significant human cancer cell growth inhibitory activity.133 An examination of the metabolites of the mollusc Philinopsis speciosa has yielded information into the interrelationships of their diet. This latest study134 has found five new depsipeptides namely kulolide-2 255 kulolide-3 256 kulokainalide-1 257 kulomo’opunalide-1 258 kulomo’opunalide-2 259 together with linear peptide pupukeamide 260 and macrolide tolytoxin 23-acetate 261. From these metabolites it has been suggested that the algal diet of sea hares and molluscs plays an important part in the creation of these more structurally complex metabolites.Cupolamide A 262 is a cytotoxic cyclic heptapeptide found in two samples of the sponge Theonella cupola.135 Another total synthesis of cyclotheonamide B 265 uses two key intermediates 263 and 264 in a flexible convergent procedure. The yield being 1.8% over seventeen steps.136 Mozamide A 266 and moxamide B 267 are new metabolites found in a sponge belonging to the Theonellid family.137 Thiocoraline 268 is a novel depsipeptide alkaloid found in the mycelium of the marine fungus Micromonospora species l- 13-ACM2 = 092. This interesting cyclic thiodepsipeptide has antitumour antibiotic properties.138 Octapeptide cyclogossine B 269 is found in the latex of the Euphorbiaceae tree Jatropha gossypifolia.139 Omphalotin is a new cyclic peptide alkaloid isolated from Omphalotus oleaurius.Its structure has been determined as 270 the structure of the decapeptide ring being established by hydrolysis followed by Nat. Prod. Rep. 2000 17 57–84 72 HMBC and NOESY correlations to determine the sequence of amino acids.140 A cyclic peptide named RP-1776 (271) has been obtained from the aerobic culture fluid of a Streptomyces species.141 Compound 271 possesses antibacterial activity. The total synthesis of himastatin 272 has resulted in a revision of its previous stereochemistry.142 Complestatin 273 and chloropectin 274 its isomeric congener are both bicyclic hexapeptides isolated from a Streptomyces species.143 Acid treatment of 273 results in the formation of 273 and it has been suggested that this transformation occurs through a cyclopropane intermediate 275.5 Miscellaneous alkaloids The fresh pods of Moringa oleifera contain an unusual glycoside called miazidin it contains an O-nitrile thiocarbamate grouping 276.144 The new lysine derivative 277 has been found in two species of marine sponges. The first was Axinyssa terpnis and the second source of this zwitterion was Axinella carteri.145 A new juvenile hormone biosynthesis inhibitor called brevioxime 278 has been isolated from the microorganism Penicillium brevicompactum. This unusual heterobicyclic ring system was identified primarily by X-ray crystallography and as the first inhibitor produced by a fungus with this type of activity.146 Macrocyclic polyamines are defence substances associated with the pupal stage of the coccinellid beetle Epitachna borealis.These are made up of large ring lactonic structures derived from a set of 2-(hydroxyethylamino)alkanoic acids. Epiachnene 279 is the simplest and the most abundant macrocyclic metabolite isolated.147 Of the more complex polyamines is 280 where n m o p and q can have values of five six or seven. The growth stimulator produced by the fungus Propiolacterium freudenreichii was found to be 2-amino-3-carboxynaphtho-1,4-quinone 281.148 (+)-Norlumicine’s structure 282 has been completely elucidated by X-ray analysis.149 73 Nat. Prod. Rep. 2000 17 57–84 Nat. Prod. Rep. 2000 17 57–84 74 3N 2Cl2 0 °C 1 h; iii NaI acetone reflux 3–4 h; iv DMPU–THF (1+1) Sixteen alkaloids have been identified as being present in the roots of Aristolochia triangularis.150 The new ones are triangularine A 283 and triangularine B 284.Lissoclin disulfide 285 is a novel dimeric alkaloid found in a bioassay guided fractionation of a methanol extract of an ascidian of the Lissoclinum family.151 The phenazine alkaloid from a marine Streptomycete species is new,152 it is 5,10-dihydrophencomycin methyl ester 286. Two phenazine alkaloids produced by a new halophilic marine bacterium called culture LL-141352 were Scheme 4 Reagents i NaH BnBr DMF 0 °C > rt 15 h; ii MsCl Et CH 215 °C 30 min to rt overnight; v excess Na ButOH NH3 Et2O 240 °C 3–4 days; vi LDA 3-picoline 307 THF 278 °C 30 min then 309 or 310; vii MCPBA CH2Cl2 0 °C 5 h to rt overnight; viii KI CH3CN reflux 4 days.identified as pelagiomicin A 287 and pelagiomicin B 286. Both are quite toxic substances.153 The tunicate Ritterella tokioka is a prolific producer of alkaloids of the ritterazine group some twenty nine compounds have been isolated. The most recent publication describes thirteen new ones namely ritterazines N to Z.154 Their structures are based largely on two hexacyclic ring systems connected through nitrogen. Thus ritterazine N is 287 O is 290 P is 291 75 Nat. Prod. Rep. 2000 17 57–84 Q is 292 while Z is 293. All thirteen alkaloids have been evaluated for cytotoxic activity and some structure activity assessment made. A stereoselective synthesis of penaresidin A 300 has been achieved starting with the Gamer aldehyde 294.155 It was first converted into its extended aldehyde 295 and when condensed with Wittig reagent 296 it gave a diastereomeric mixture at C15 and C16 297.Ring opening of the N,O-acetonide gave after protection and mesylation of the hydroxy groups 298. Ring closure of the azetane 299 then proceeded to give penaresidin A 300. Several amino acids of a non-protein nature have been isolated from the seeds of Cycas revoluta.156 Two new ones are Nat. Prod. Rep. 2000 17 57–84 76 cycasindene 301 and cycasthioamide 302. Haliclamine A 316 is said to be biogenetically related to the manzamines in that it is the nearest bisdihydropyridine so far found naturally. Its total synthesis has been reported.157 Butane-1,4-diol (303) was modified to the protected mesylate 304 which could be condensed with lithioalkyne 305 to give 306 which upon reduction with sodium metal in tert-butyl alcohol simultaneously removed the protecting group and produced E-alkene 307 which was mesylated and iodinated to give 309.In a similar manner related alkyl chain 310 was prepared and it remained for both to be attached to 3-methylpyridine (311). This was achieved by LDA activation of the methyl-group on 311 and attachment occurred by iodide displacement to give 312 and thence to the mesylate 314. Similarly 316 was prepared from 310 and 3-methylpyridine (311). Protection of the heterocyclic nitrogen in 314 by N-oxide formation 315 enabled it to condense with 316 giving 317. Mesylation and N-deoxygenation allowed ring closure where upon sodium borohydride reduction resulted in the formation of haliclamine A 318 (Scheme 4).Malonylniphimycin 319 is a macrolide antibiotic obtained from the culture fluid of Streptomyces hygroscopicus B-7.158 Polaramycin A 320 and polaramycin B 321 are two new antifungal antibiotics isolated from the culture fluid of hygroscopicus species LP-93.159 Some fourteen alkaloids have been isolated from the prosobranch mollusc Lamellaria in the past fourteen years and now the first synthesis of lamarin class marine alkaloids namely laminarin D 327 and laminarin H 328 has been reported.160 Firstly benzylisoquinoline 322 synthesised in a conventional procedure was condensed with ester 323 through the use of LDA to give 324.Quaternization of 324 with ethyl bromoacetate gave 325 which could be cyclised to the laminarin type structure 326 through removal of the MOM protecting group and treatment of the resulting phenol with triethylamine – all in a one pot procedure. Finally removal of the benzyl protecting groups gave laminarin D 327. Lamarin H 328 was also synthesised from 326 through simultaneous Odemethylation and deprotection with BBr3. A different synthetic approach is the convergent synthesis of lamellarin K 333. In this procedure161 an intramolecular [3+2] cycloaddition of 331 occurred in situ when 329 and 330 were mixed in dichloroethane in the presence of Hunig’s base and heated to 83 °C giving 332. Removal of the isopropyl ether groups with aluminium trichloride produced alkaloid 333.The shrub originating from Lijiang in China Cephalotaxus forturnei has been found to contain three alkaloids;162 the new one is called fortunine and its structure is 334. A stereocontrolled synthesis of (±)-9,10-dideoxynorribasine 338 an alkaloid found in Fumariaceae plants was successfully completed163 by treating cis-2-amino-1-inandol 335 to aqueous basic conditions whereupon the nitrile group was hydrolysed and intramolecularly cyclised to 336. This lactam was reduced to aminoindanol 336 which with Fremy’s salt produced indanobenzazepine 338 and thence to alkaloid 339. This synthetic procedure has also been applied to the synthesis of (±)-ribasin 340.164 Makaluvic acid A 341 and makaluvic acid B 342 are novel alkaloids found in the sponge Zyzzya fuliginosus.165 Hanishin 343 is a semi-racemic bioactive C9 alkaloid found in the axinellid sponge Acanthella carterie.166 It is thought that this metabolite is a degradation product of other metabolites found in this sponge as these are all C11 containing metabolites e.g.oroidin. Nothapodytine A 344 and nothapodytine B 345 are constituents of the stems of Nothapodytes foetida. Although this stem extract displayed significant cytotoxic activity no assess- Nat. Prod. Rep. 2000 17 57–84 77 ment of these alkaloids activity was reported.167 Two new pyrroloquinqaolinoquinoline alkaloids have been isolated from the ariel parts of Peganum nigellastrum. Called luotonins A and luotonius B they are 346 and 347 respectively.168 Nat.Prod. Rep. 2000 17 57–84 78 Four alkaloids obtained from the marine sponge Aaptos aaptos have been identified as dimethyl(oxy)aaptamine 348 and aaptosine 349 and the known alkaloids aaptamine and isoaaptamine. 169 The first reported synthesis of isotatzelline B 353 is based on the creation of the ring system 1,3,4,5-tetrahydropyrrolo- [4,3,2,de]quinoline common to a wide range of marine alkaloids. Reduction of 350 (i NaBH4 NiCl2 ii HCO2H) and ring closure gave 351. This was followed by introduction of the methylthio group (MeSSMe SO2Cl2) and oxidation to quinone 352 which enabled the amino group to be introduced leading to isobatzelline B 353.170 Eupomatidines are alkaloids containing the iminoquinoline quinone structure e.g.eupomatidine 2 354. Through an aza Diels–Alder reaction between 355 and 356 followed by condensation with DMF–diethyl acetal the crude imine 357 so Scheme 5 Reagents i NaI acetone 50 °C 16 h filter then tetrahydrothiophene AgBF4 rt 1 h; ii ButLi THF 278 °C 15 min then 9-bromononanal 278 °C to rt; iii Methyl (phenylsulfonyl)acetate KH 3 mmol DMF rt then 394 DMF rt 72 h; iv Pd(PPh 6 h reflux; v TBAF NH 3)4 dppe THF then 395 4F THF rt 30 min; vi Dess–Martin periodane reagent; vii BnNH2 Pd(Ph3P) THF 35 °C 1.5 h; viii 1-(N,N- 2Cl2 2 h rt; ix ZnCl2 dimethylamino)-1-chloro-2-methylprop-1-ene CH TMEDA THF MeLi 0 °C 15 min then PriMgCl THF 5 min then 400; x Ca liq NH3 THF 230 °C 2 h; xi KH DMF rt 5 min then SEMCl 45 min rt; xii BunLi THF 278 °C argon 30 min rt ZnCl2 278 °C to 0 °C then Pd(PPh3)4 THF and 403; xiii pyridinium toluene-p-sulfonate MeOH 55 °C 14 h; xiv KH THF 0 °C TIPSCl 30 min rt; xv BunLi THF 250 °C 5 h; xvi CeCl3 THF 278 °C 5 h then 401 2 h 278 °C to rt; xvii TBAF THF rt 10 min; 60 °C 45 min.produced could be cyclised to 354. Modification of naphthoquinone 355 led to the other eupomatidines.171 An extension of this synthetic procedure using azadiene 359 and a quinoline dione 358 has resulted in the synthesis of the pentacyclic azaaromatic alkaloid cystodamine 360.172 Plakinidine D 361 is a new pyrroloacridine alkaloid found in a previously undescribed red coloured Didemnum species.173 Extraction of Didemnum rubeus produced not only plakinidine D but also 3,5-diiodo-4-methoxyphenylethylamine.A consecutive publication174 also describes the isolation of this alkaloid together with 11-deoxyplakinidine D 362. Three steps were used to synthesis the pentacyclic alkaloid kuanoniamine A 365.175 Condensation of 6-methoxybenzothiazole-4,7-dione 363 with 2-aminoacetophenone gave the anilinoquinone 364 directly when CeCl3 was used in the presence of air. 79 Nat. Prod. Rep. 2000 17 57–84 Introduction of the aminoethylene side chain 365 was followed by ring closure to kuanoniamine 366. Using quinolinedione 367 resulted in the synthesis of neocalliactine acetate 368. Bioactive pyridoacridine alkaloids have been found in a species of the Micronesian sponge Oceanapia. All belong to the kuanoniamine type.176 Known kuanoniamine C 369 and kuanoniamine D 370 were found together with a new one Ndeacetylkuanoniamine 371.Asperazine 372 is a selective cytotoxic alkaloid obtained from a culture of Aspergillus niger growing on a saltwater Caribbean sponge belonging to the Hyrtios family.177 Antibiotic RF-1061 373 and its analogues can be prepared from the fungus Streptomyces species SN-1061M which is a mutant of Streptomyces species RK-1061.178 Dragmacidin E 374 is the newest member of metabolites obtained from the deep water Australian marine sponge of the Spongosorites species. It possesses a fluorescent yellow colour and is an active inhibitor of protein phosphatase.179 Moschamide 375 is an alkaloid found in the seeds of Centaurea moschata.Extensive spectroscopic analysis revealed its unusual structure.180 A series of antibacterial agents have been manufactured using an Actunomadura fungus species A45722. The active principal metabolite is BE-45772 376. Derivatives include substitution at the pyrrole itself.181 Callipeltoside A and callipeltoside B are two novel cytotoxic metabolites obtained from the marine lithistid sponge Callipelta.182 Both contain macrolide rings with heterocyclic appendages as indicated by 377 for A and 378 for B. A novel platelet activating factor and acetyltransferase inhibitor has been obtained from Penicillium rubrum.183 Extensive NMR studies on ZG-1494a have suggested it to have structure 379. Callipeltoside A 380 is a cytotoxic macrolide of a new type isolated from the marine lithistida sponge of the Callipelta family.184 Scheme 6 The sponge Batzella after a large scale extraction and examination has produced nineteen guanidine alkaloids;185 typical are the three new ones 8a,8b,dehydro-ptilocaulin 381 8a,8b-dehydro-8-hydroxyptilocaulin 382 and 1,8a;8b,3a-dihydro-8-hydroxyptilocaulin 383.Hydroxyakalone 384 is a novel xanthine oxidase inhibitor produced by the marine bacterium Agrobacterium aurantiacum.186 Some new saxitoxin analogues have been obtained from the fresh water mat-forming filamentous cyanobacterium Lyngbya wollei.188 All are based on saxitoxin 386 itself. Agelastatin C 387 and agelastatin D 388 are two new tetracyclic pyrroles found in a marine sponge of the Cymbastela family.189 The ‘living fossil’ sponge Astrosclera willeyana has been found to contain a metabolite with an unprecedented structure.Called A new purine metabolite erinacean 385 was found in the sponge Isodictya erinecea with antifeedant properties towards the antartic sponge predator Perknaster fuscus.187 Nat. Prod. Rep. 2000 17 57–84 80 manzacidin D 389 it contains the unusual unbrominated non Nmethylated pyrrole addendum.190 Konbu’acidin A 390 is an alkaloid isolated from an Hymeniacidon sponge.191 Compound 390 showed inhibitory activity against cyclin dependent kinase 4. A new member of the banumycin group of antibiotics has the ability to convert rastransformed cells NiH3T3 and T cells back into normal. The toxicology isolation biological characterisation and structure of 391 are described in detail.192 The first total synthesis of roseophilin 410 an antitumour agent produced by Streptomyces griseoviridis has been reported.193 The molecule can be made up of two entities a macrotricyclic component and a furanopyrrole. In the first case protected chlorobutene 392 condensed with tetrahydrothiophene via a halide exchange (chlorine to iodine) to give 393 which upon treatment with base gave the ylide for reaction with 9-bromononanal thereby generating oxirane 394. Introduction of the methyl(sulfonyl)acetate grouping gave 395 which was found to smoothly cyclise to the eighteen membered ring by treatment with a Pd[0] reagent. Desilylation gave the strained lactone 397 which upon Dess–Martin oxidation and treatment of the ketone 398 with another Pd[0] catalyst and benzylamine produced pyrrole 399 which could be cyclised to ketone 400.A 1,4-elimination and concomitant introduction of an isopropyl group created 401 which was deprotected and reprotected by the SEM group 402. The thiophenepyrrole synthon 405 was made from acid chloride 403 and pyrrolester 404 which combined to give 405 and hence 406. Combination of 402 and 406 occurred by converting the chloropyrrole 406 into its cerium derivative 408 thus giving the protected natural product 409 whereupon deprotection gave the red coloured salt of roseophilin hydrochloride 410 Scheme 5. The dried rhizomes of the Nuphar pumilum plant have been shown to contain four new thiasperane sulfoxide type dimeric alkaloids called nupharpumilamine A 411 nupharpumilamine B 412 nupharpumilamine C 413 and nupharpumilamine D 414 they all possess immunosuppressive activity.194 A revised structure for araguspongine B 415 and araguspongine E 416 has been suggested in that the C-9 stereochemistry is reversed.195 The absolute stereochemistry of isosaraine-1 417 and isosaraine 2 418 has been determined by applying the Mosher procedure.196 Two new alkaloids have been obtained from the roots of Isatis indigolica.197 X-Ray measurements combined with spectral analyses established the structures of isaindigotidione 1 as 419 and isaindigotone 2 as 420.Spirotryprostatin 421 is a cell cycle inhibitor and an antitumour agent which was produced by Aspergillus fumigatus.198 Lymphostin (LK6-A) is a novel immunosuppressant isolated from the culture broth of Streptomyces SP KY11783.199 Its structure contains the novel aromatic tricyclic ring system 422.Madangamines B to E are pentacyclic alkaloids obtained from the marine sponge Xestospongia ingens.200 Structural variation occurs in the ring designated X thus B is 423 C is 424 D is 425 and E is 426. A novel hexacyclic manzamine related alkaloid has been isolated from an Amphimedon sponge.201 Structurally it has been shown to have a novel furan ring 427 and it is proposed that it is biosynthesised from ircinol A 428. The first total synthesis of a number of these manzamine and related alkaloids has been reported.202 The novel pentacyclic ring system common to these alkaloids is based on ircinol A 428 which was synthesised rather elegantly starting from the secondary amine 429 which combined with 430 to give vinylogous amide 431.This amide 431 upon irradiation induced a photoaddition and retro-Mannich fragmentation through O-closure of the ketoiminium intermediate 432 to give aminal 434 presumably via 433. On treatment with pyridinium acetate this aminal 434 isomerized to the mangamine tetracycle 435. Manipulation of the substituents on ring B created 436 which could be ring closed to 437 and thence to manzamine A 438. 6 References 1 O. Hoshino Alkaloids (Academic Press) 1998 51 324. 2 R. M. Moraes-Cerdira C. L. Burandt J. K. Bastos N. P. N. Dhammika J. Mikell J. Thurn and J. D.McChesmey Planta Med. 1997 63 472; (Chem. Abstr. 1998 127 283247). 3 M. Selles J. Bastido F. Viladomat and C. Codina Analusis 1997 25 156; (Chem. Abstr. 1998 127 268097). 4 M. Selles S. Bergonon F. Viladamat J. Bastida and C. Codina Plant Cell Tissue Organ Cult. 1997 49 129; (Chem. Abstr. 1998 127 290600). 5 J. R. Lewis Rodd’s Chemistry of Carbon Compounds ed. M. Sainsbury Elsevier 1997 2nd suppl. vol. 4 part B 1997 165. 6 J. R. Lewis Nat. Prod. Rep. 1998 15 107. 7 D. A. Chaplin N. Fraser and P. D. Tiffin Tetrahedron Lett. 1997 38 8 L. Czollner W. Frantsits B. K�uenburg U. Hedenig J. Fr�ohlich and U. 9 D. A. Chaplin N. R. Johnson J. M. Paul and G. A. Potter PCT. Int. 7931. Jordis Tetrahedron Lett. 1998 39 2087. Appl. WO9745 431; (Chem.Abstr. 1998 128 61674). 10 W. E. Campbell J. J. Nair D. W. Gammon J. Bastida C. Codina F. Viladomat P. J. Smith and C. F. Albrecht Planta Med. 1998 64 91; (Chem. Abstr. 1998 128 221515). 11 T. B. H. Vo K. Q. C. Nguyen and V. T. Ngo Tap. Chi. Duoc Hoc 1997 9; (Chem. Abstr. 1998 128 292716). 12 T. H. Ngnyen B. D. Tran T. A. Nguyen and T. S. Phan Hoa Hoc Cong Nghiep Hoa Chat 1997 13; (Chem. Abstr. 1998 128 255168). 13 T. Van Sung and P. L. Trinh Tap Chi Hoa Hoc 1997 35 64; (Chem. Abstr. 1998 127 217828). 14 Z. Trimino C. Iglesias M. Iglesias I. Spengler and M. Basterrechea Rev. Cubana Quim. 1997 9 123; (Chem. Abstr. 1998 128 268257). 15 Z. Trimino C. Iglesias M. Iglesias I. Spengler and M. Basterrechea Rev. Cubana Quim. 1997 9 119; (Chem. Abstr.1998 129 268256). 16 M. Gehlung H.-F. Moeschler R. Velten D. Wendisch W. Andersch C. Erdelen A. Harder N. Mencke A. Turberg and U. Wachendorff- Neumann Ger. Offen. DE 19,610,279; (Chem. Abstr. 1997 127 278406). 17 R. Velten C. Erdelen G. Matthias A. Gohrt D. Gondol J. Lenz O. Lockoff U. Wachendorff and D. Wendish Tetrahedron Lett. 1998 39 1737. 18 N. Kushida S. Atsumi T. Koyano and K. Umezawa Drugs Exp. Clin. Res. 1997 23 151; (Chem. Abstr. 1998 128 136246). 19 Z. Trimino I. Spengler J. Borrego C. Iglesias G. W. Depke and E. Swerin Rev. Cubana Quim 1996 8 53; (Chem. Abstr. 1998 28 255165). 20 F. Viladomat M. Selles C. Codina and J. Bastida Planta Med. 1997 63 583; (Chem. Abstr. 1998 128 106290). 21 F. Viladomat C. Codina J. Bastida X.Solans and M. Font-Bardia Acta Cryst. Sect. C Cryst. Struct. Commun. 1998 C54 81; (Chem. Abstr. 1998 128 167582). 22 T. Sarg M. Zenk S. El-Dahmy A. Abdel Ghani and M. Abou- Hoshem Bull. Fac. Pharm. (Cairo Univ.) 1997 35 159; (Chem. Abstr. 1998 128 99820). 23 Y. Kita T. Takedo M. Gyoten H. Tohma M. H. Zenk and J. Eirchhorn J. Org. Chem. 1996 61 5857. 24 H. W. Shao and J. C. Cai Chin. Chem. Lett. 1997 8 493; (Chem. Abstr. 1997 127 135976). 25 J. H. Rigby and M. E. Mateo J. Am. Chem. Soc. 1997 119 12655. 26 T.-J. Doyle M. Hendrix D. Van Derveer S. Javanmard and J. Haseltine Tetrahedron 1997 53 11153. 27 B. M. Trost and S. R. Pulley J. Am. Chem. Soc. 1995 117 10143. 28 T. Harayama T. Akiyama and K. Kawano Chem. Pharm. Bull. 1996 44 1634. 29 J.Jin and S. M. Weinreb J. Am. Chem. Soc. 1997 119 2050. 30 J. Jin and S. M. Weinreb J. Am. Chem. Soc. 1997 119 5773. 31 J. H. Rigby A. Cavezza and J. M. Heeg J. Am. Chem. Soc. 1998 120 32 V. Pabuccuoglu and M. Hesse Heterocycles 1997 45 1751; (Chem. 33 J. C. Norrild and C. Pedersen Synthesis 1997 1128; (Chem. Abstr. 34 A. Olofson K. Yakushijin and D. A. Horne J. Org. Chem. 1998 63 35 A. Terpin C. Winkloher S. Schumann and W. Steglich Tetrahedron 3664. Abstr. 1997 127 293444). 1997 127 358974). 1248. 1998 54 1745. 81 Nat. Prod. Rep. 2000 17 57–84 36 T. Tajika I. Bando T. Furuta N. Moriya H. Koshino and M. Uramoto Biosci. Biotechnol. Biochem. 1997 61 1007; (Chem. Abstr. 1997 127 187912). 37 K. Kanoh S. Kohno T. Asari T. Harada J. Katada M.Muramatsu H. Kawashima H. Sekiya and I. Uno Bioorg. Med. Chem. Lett. 1997 7 38 I. Duranton M. Tane M. Avella and P. Poujeol Bioorg. Med. Chem. 39 J. Kobayashi K. Inaba and M. Tsuda Tetrahedron 1997 53 40 S. Daninos-Zeghal Ali Al Mourabit A. Ahond C. Poupat and P. 2847; (Chem. Abstr. 1998 128 86272). Lett. 1997 7 2283. (Chem. Abstr. 1997 127 305548). 16679. Potier Tetrahedron 1997 53 7605. 41 T. Lindel and H. Hoffmann Tetrahedron Lett. 1997 38 8935. 42 O. S. Radchenko V. L. Novikov R. H. Willis P. T. Murphy and G. B. Elyakov Tetrahedron Lett. 1997 38 3581. 43 X. Fu F. J. Schmitz R. S. Tanner and M. Kelly-Borges J. Nat. Prod. 1998 61 384. 44 A. Plubrukam D. W. Smith R. E. Cramer and B. S. Davidson J. Nat. Prod. 1997 60 712. 45 I.Kawasaki N. Taguchi M. Yamashita and S. Ohta Chem. Pharm. Bull. 1997 45 1393. 46 K. C. Nicolalou S. Kim J. Pfefferkorn J. Zu T. Ohshima S. Hosokawa D. Vourloumis and T. Li Angw. Chem. Int. Ed. 1998 37 1418. 47 Anon J. Antibiotics 1997 50 712; (Chem. Abstr. 1997 127 259852). 48 T. Sasaki T. Otani K.-I. Yoshida N. Unemi M. Hamada and T. Takeuchi J. Antibiot. 1997 50 881; (Chem. Abstr. 1998 128 32166). 49 P. Radford A. B. Attygalle and J. Meinwald J. Nat. Prod. 1997 60 755. 50 S. Takahashi T. Matsunaga C. Hasegawa H. Saito D. Fiyita F. Kiuchi and Y. Tsuda Toyama-ken Yakuji Kenkyusho Nenpo 1996 24 51 D. R. Williams K. M. Werner and B. Feng Tetrahedron Lett. 1997 52 J. D. White C. S. Nylund and N. J. Green Tetrahedron Lett. 1997 38 53 J. D.White M. A. Holoboski and N. J. Green Tetrahedron Lett. 1997 54 P. Ciminiello E. Fatturusso M. Formo and S. Magno Tetrahedron 55 S. Matsunga T. Wakimoto N. Fusetani and M. Suganuma Tetra- 53; (Chem. Abstr. 1998 128 72758). 38 6825. 7329. 38 7333. 1997 53 6565. hedron Lett. 1997 38 3763. 56 J. R. Lewis Nat. Prod. Rep. 1996 12 135. 57 G. Ryu S. Hwang and S.-K. Kim J. Antibiot. 1996 50 1064; (Chem. Abstr. 1998 128 164767). 58 A. K. Ghosh and W. Liu J. Org. Chem. 1997 62 908. 59 R. K. Kondru P. Wipf and D. N. Beratan J. Am. Chem. Soc. 1998 120 2204. 60 C. J. Moody and M. C. Bagley J. Chem. Soc. Perkin Trans. 1 1998 601. 61 H. Sone H. Kigoshi and K. Yamada Tetrahedron 1997 53 8149. 62 G. R. Pettit J.-P. Xu M. D. Williams F. Hogan and J.M. Schmidt Bioorg. Med. Chem. Lett. 1997 7 827; (Chem. Abstr. 1997 127 3099). 63 M. Z. Hoemann K. A. Agrios and J. Aube Tetrahedron 1997 53 1087. 64 G. Hofle H. Reichenbach H. Irschik and R. Jansen PCI Int. Appl. WO97 18 217; (Chem. Abstr. 1997 127 32937). 65 R. M. Rzasa H. A. Shea and D. Romo J. Am. Chem. Soc. 1998 120 591. 66 J. C. Nicolaou N. Winssinger J. Pastor S. Nukovic F. Sarabia Y. He D. Vourloumis Z. Yang T. Li P. Giannakakou and E. Hamel Nature 1997 387 268. 67 L. Chill Y. Kashman and M. Schleyer Tetrahedron 1997 52 16147. 68 N. Kuriyama K. Akaji and Y. Kiso Tetrahedron 1997 53 8323. 69 J. R. Lewis Nat. Prod. Rep. 1992 9 81. 70 A. D. Patil A. J. Freyer L. Killmer C. Chamberjers and R. K. Johnson Nat. Prod. Lett.1997 9 181; (Chem. Abstr. 1997 127 159205). 71 M. S. Puar T. M. Chan V. Hegde M. Patel P. Bartner K. J. Ng B. N. Pramanik and R. D. Macfarlane J. Antibiot. 1998 51 221; 72 Attar-Ur-Rahman M. I. Choudhary A. Majeed A. M. M. Stabbir U. 73 H. J. Shin H. Matsudo M. Murakami and K. Yamaguchi Tetra- 74 I. Tanaka S. Matsuoka M. Murata and K. Tachibana J. Nat. Prod. (Chem. Abstr. 1998 128 280634). Ghani and M. Shameel Phytochemistry 1997 46 1215. hedron 1997 53 5747. 1998 61 685. Nat. Prod. Rep. 2000 17 57–84 82 75 A. Valla M. Giraud R. Labia and A. Morand Bull. Soc. Chem. Fr. 1997 134 601. 76 T. Hu J. V. Schaus K. Lam M. G. Palfreyman M. Wuonola G. Guistafson and J. S. Panek J. Org. Chem. 1998 63 2401. 77 K. Pari P. J. Rao C. Devakumar and J.N. Rastogi J. Nat. Prod. 1998 61 102. 78 M. Ueda C. Tashiro and S. Yamamura Tetrahedron Lett. 1997 38 3253. 79 H. Noguchi T. Aoyama and T. Shioiri Tetrahedron Lett. 1997 38 2883. 80 N. Matsumoto T. Tsuchida M. Umekita N. Kusoshita H. Iinuma T. Sawa M. Hamada and T. Takeuchi J. Antibiot. 1997 50 900; (Chem. Abstr. 1998 128 72713). 81 N. Matsumoto T. Tsuchida R. Sawa H. Ginuma H. Nagamawa T. Sawa and T. Takeuchie J. Antibiot. 1998 50 912; (Chem. Abstr. 1998 128 72712). 82 L. Kraut T. Klaus R. Mues T. Eicher and H. D. Zinmeister Phytochemistry 1997 45 1621. 83 K. Yoshikawa T. Takadera K. Adachi M. Nishijima and H. Sano J. Antibiot. 1997 50 949; (Chem. Abstr. 1998 128 72718). 84 S. Kitano T. Sasaki K. Yoshida T. Otani L. Yu Y. Wu and N. Katsunnuma PCT Int.Appl. WO 9731 122; (Chem. Abstr. 1997 127 306677). 127 204536). 85 Y. Kan T. Fujita H. Nagai B. Sakamoto and Y. Hokama J. Nat. Prod. 1998 61 152. 86 A. Numata T. Amagata K. Minoura and T. Ito Tetrahedron Lett. 1997 38 5675. 87 T. Tanaka F. Koizumi T. Agatsuma H. Kondo Y. Saitoh K. Ando and Y. Matsuda PCT Int. Appl. WO 9737 034; (Chem. Abstr. 1997 88 M. P. Singh M. J. Mroczenski D. A. Steinberg R. J. Andersen W. M. Maiese and M. Greenstein J. Antibiot. 1997 50 270; (Chem. Abstr. 1997 127 47611). 89 K. Ishida H. Matsuda M. Murakami and K. Yamaguchi Tetrahedron 1997 53 10281. 90 K. Shin-ya J.-S. Kim K. Furihata Y. Hayakawa and H. Seto Tetrahedron Lett. 1997 38 7079. 91 C. Qi Y. Zhen W. Chen Faming Zhuanli Shenquing Gongkai Shuomingshu CN 1,124 778; (Chem.Abstr. 1998 128 320647). 92 C. Yuan and R. M. Williams J. Am. Chem. Soc. 1997 119 11777. 93 K. L. Erickson J. A. Beutler J. H. Cardellina II and M. R. Boyd J. Org. Chem. 1997 62 8188. 94 J. A. Palermo M. F. R. Braseo E. Cabezas V. Balzaretti and A. M. Seldes J. Nat. Prod. 1998 61 488. 95 C.-Y. Chen F.-R. Chang and Y.-C. Wu Tetrahedron Lett. 1998 39 407. 96 J. R. Telford and K. N. Raymond J. Biol. Inorg. Chem. 1997 2 75; (Chem. Abstr. 1998 128 190238). 97 T. Feh J. Valerie J.-J. Sanglier L. Oberer L. Gschwind M. Ponelle W. Shilling S. Wehrli A. Enz G. Zenke and W. Schuler J. Antibiot. 1997 50 893; (Chem. Abstr. 1998 128 72706). 98 K.-I. Suzumura I. Takahashi H. Matsumoto K. Nagai B. Setiawan R. M. Rantiatmojo K.-I.Suzuki and N. Nagano Tetrahedron Lett. 1997 38 7573. 99 D. L. Galinis T. C. McKnee L. K. Pannell J. H. Cardellina II and M. R. Boyd J. Org. Chem. 1997 62 8968. 100 S. Hisano T. Ito M. Goto S. Kazuhiro N. Suenobu and K. Goto Jpn. Kokai Tokkyo Koho 10 45 747; (Chem. Abstr. 1998 128 229419). 101 M. Ueki A. Kusumoto M. Hanafi K. Shabata T. Tanaka and M. Taniguchi J. Antibiot. 1997 50 551; (Chem. Abstr. 1997 127 217524). 102 R. Donos A. Rivera-Sagredo J. A. Hueso-Rodriques and S. W. Elson Nat. Prod. Lett. 1997 10 49; (Chem. Abstr. 1997 127 62967). 103 H. Kakeya M. Morishita C. Onozowa R. Usami K. Horikoshi K. Kimura M. Yoshimama and H. Osada J. Nat. Prod. 1997 60 669. 104 C. Wagner H. Anke and O. Sterner J. Nat. Prod. 1998 61 501. 105 B.Wu and D. Bai J. Org. Chem. 1997 62 5978. 106 T. F. Solov’eva B. P. Baskunov and T. A. Reshitov Prikl. Bikhim. 107 A. Espada A. Rivera-Sagredo J. M. de la Fuente J. A. Hueso- 108 M. V. D’Auria C. Giannini L. Minale A. Zampella C. Debitus and 109 P. Kuchne A. Guggisberg and M. Hesse Helv. Chim. Acta 1997 80 Mikrobiol. 1997 33 66; (Chem. Abstr. 1997 127 92499). Rodriques and S. W. Elson Tetrahedron 1997 53 6485. M. Frostin J. Nat. Prod. 1997 60 814. 1802. 110 J. R. Lewis Nat. Prod. Rep. 1999 16 389. 111 U. A. Hausermann and M. Hesse Tetrahedron Lett. 1998 39 257. 112 F. Fang H. Hi K. Shiomi R. Masuma Y. Yamaguchi G. G. Zhang X. W. Zhang Y. Tamaka and S. Omura J. Antibiot. 1997 50 919; (Chem. Abstr. 1998 128 72715). 113 M. Boehler P. R.Jensen and W. Fenical Nat. Prod. Lett. 1997 10 75; (Chem. Abstr. 1997 127 31339). 114 X. Obayashi T. Yoshimura Y. Ikenoue R. Fudo M. Murata and T. Ando PCT Int. Appl. WO 9744 479; (Chem. Abstr. 1998 128 47384). 115 H. H. Wasserman and A. K. Petersen J. Org. Chem. 1997 62 8972. 116 A. K. Dexit and L. N. Misra J. Nat. Prod. 1997 60 1036. 117 K. Drandarov Phytochemistry 1997 44 971. 118 A. Hirano B. Nakajima H. Suzuki K. Ojiri and H. Suda Jpn. Kokai Tokkyo Koho 0987284; (Chem. Abstr. 1997 127 16574). 119 K. M. Gardiner and J. W. Leahy J. Org. Chem. 1997 62 7098. 120 T. Takatsu A. Muramatsu M. Otsuki S. Kurakata and R. Enokida Jpn. Kokai Tokkyo Koho 09286779; (Chem. Abstr. 1998 128 21927). 121 T. Shiori I. Imaeda and Y. Hamada Heterocycles 1997 46 421; (Chem.Abstr. 1998 128 270859). 122 M. Igarashi T. Tsuchida N. Kimoshita M. Kamijima R. Sawa H. Naganawa M. Hamada T. Takeuchi K. Yamazaki and M. Ishizuka J. Antibiot. 1998 51 1231; (Chem. Abstr. 1998 128 268002). 123 I. R. Marsh M. Bradley and S. J. Teague J. Org. Chem. 1997 62 6199. 124 W. D. Clark T. Corbett F. Valeriote and P. Crews J. Am. Chem. Soc. 1997 119 9285. 125 C. E. Masse M. Yang J. Soloman and J. S. Panek J. Am. Chem. Soc. 1998 120 4123. 126 J. S. Panek F. Xu and A. C. Rondon J. Am. Chem. Soc. 1998 120 4113. 127 W. R. Roush D. S. Coffey and D. J. Madar J. Am. Chem. Soc. 1997 119 11331. 128 S.-G. Cao X.-H. Wu K.-Y. Sim B. K. H. Tan J. T. Pereira and S.-H. Goh Tetrahedron 1998 54 2143. 129 A. S. R. Ammanamanchi K.S. Sagar and N. S. K. Rao Nat. Prod. Lett. 1997 11 5; (Chem. Abstr. 1998 128 190575). 130 A. F. Morel E. C. S. Machado J. J. Moreira A. S. Memezis M. A. Mostardeiro N. Zanatta and L. A. Wessjohann Phytochemistry 1997 47 125. 131 K. M. Jenkins M. K. Renner P. R. Jensen and W. Fenical Tetrahedron Lett. 1998 39 2463. 132 G. R. Pettit J.-P. Xu F. Hogan M. D. Williams D. L. Doubek J. M. Schmidt R. L. Cerny and M. R. Boyd J. Nat. Prod. 1997 60 752. 133 G. R. Pettit J.-P. Xu F. Hogan and R. L. Cerny Heterocycles 1998 47 491; (Chem. Abstr. 1998 128 280953). 134 Y. Nakao W. Y. Yoshida C. M. Szabo B. J. Baker and P. J. Scheuer J. Org. Chem. 1998 63 3272. 135 L. S. Bonnington J. Tanaka T. Higa J. Kimura Y. Yoshimura Y. Nakao W. Y. Yoshida and P. J.Scheuer J. Org. Chem. 1997 62 7765. 136 H. M. M. Bastiaans J. L. van der Baan and H. C. J. Ottenheijm J. Org. Chem. 1997 62 3880. 137 E. W. Schmidt M. K. Harper and D. J. Faulkner J. Nat. Prod. 1997 60 779. 138 J. P. Baz L. M. Canedo J. L. F. Puentes and M. V. S. Elipe J. Antibiot. 1997 50 738; (Chem. Abstr. 1997 127 316605). 139 C. Auvun-Guette C. Baraguey A. Blond Jean-Louis Pousset and B. Bodo J. Nat. Prod. 1997 60 1155. 140 O. Sterner A. Mayer and H. Anke Nat. Prod. Lett. 1997 10 33; (Chem. Abstr. 1997 127 62966). 141 S. Toki T. Azuma H. Saito K. Ochiai K. Ando and Y. Matsuda Jpn. Kokai Tokkyo Koho 09,227,594; (Chem. Abstr. 1997 127 189743). 142 T. M. Kamenecka and S. J. Danishefsky Angew. Chem. Int. Ed. 1998 37 2995. 143 H. Jayasuriya G.M. Salitiro S. K. Smith J. V. Heck S. J. Gould S. B. Singh C. F. Homnick M. K. Holloway S. M. Pitzenberger and M. A. Patane Tetrahedron Lett. 1998 39 2247. 144 S. Faizi B. S. Siddiqui R. Saleem F. Noor and S. Husnain J. Nat. Prod. 1997 60 1317. 145 C.-J. Li F.-J. Schmitz and M. Kelly-Borges J. Nat. Prod. 1998 61 387. 146 P. Moyo M. Castillo E. Primo-Yufera F. Gouitland R. Martines- Manez M. D. Garcera M. A. Miranda J. Primo and R. Martinez- Pardo J. Org. Chem. 1997 62 8544. 147 F. C. Schroder J. J. Fermer A. B. Attygalle S. R. Sinedley T. Eisner and J. Meinwald Science 1998 281 428. 148 H. Mori Y. Sato N. Taketoma T. Kamiyama Y. Yoshiyama S. Meguro H. Sato and T. Kaneko J. Dairy Sci. 1997 80 1959; (Chem. Abstr. 1997 127 316616). 149 E.Tykarska M. Chrzanowsha and Z. Kosturkiewicz Pol. J. Chem. 1998 72 433; (Chem. Abstr. 1998 128 205001). 150 W. Lin H. Fu H. Yoshio and N. Taro J. Chin. Pharm. Sci. 1997 61 8; (Chem. Abstr. 1997 127 290547). 151 A. D. Patil A. J. Freyer L. Killmer G. Zuber B. Carte A. J. Jurewicz and R. K. Johnson Nat. Prod. Lett. 1997 10 225; (Chem. Abstr. 1997 127 232111). 152 K. Pusecker H. Laatsch E. Helmke and H. Weyland J. Antibiot. 1997 50 479; (Chem. Abstr. 1997 127 146903). 153 M. P. Singh A. T. Menendex P. J. Petersen W.-D. Ding M. William and M. Greenstein J. Antibiot. 1997 50 785; (Chem. Abstr. 1997 127 316741). 154 S. Fukuzawa S. Matsunaga and N. Fusetani J. Org. Chem. 1997 62 4484. 155 S. Knapp and Y. Dong Tetrahedron Lett. 1997 38 3813.156 M. Pan T. J. Mabry J. M. Beale and B. M. Mamiya Phytochemistry 1997 45 517. 157 Y. Morimoto and C. Yokoe Tetrahedron Lett. 1997 38 8981. 158 V. Ivanova and A. Gushterova J. Antibiot. 1997 50 965; (Chem. Abstr. 1998 128 72720). 159 W. Jin W. Meng Y. Wang C. Zhu W. Zhang and X. Xu Zhongguo Kangshengsu Zazhi 1997 22 1; (Chem. Abstr. 1998 128 2927). 160 F. Ishibashi Y. Miyazaki and M. Iwao Tetrahedron 1997 53 5951. 161 M. Banwell B. Flynn and D. Hockless Chem. Commun. 1997 2258. 162 M. Qui B. Lu X. Ma and R. Nei Yunnan Zhiwu Yanjiu 1997 19 97; (Chem. Abstr. 1997 127 275355). 163 L. Ollero L. Castedo and D. Dominguez Tetrahedron Lett. 1997 38 5723. 164 L. Ollero L. Castedo and D. Dominguez Tetrahedron Lett. 1998 39 1413. 165 X. Fu P.-L.Ng F. J. Schmitz M. B. Hossain D. van der Helm and M. Kelly-Borges J. Nat. Prod. 1996 59 1104. 166 I. Mancini G. Guella P. Amada C. Raussakis and F. Pietra Tetrahedron Lett. 1997 38 6271. 167 T.-S. Wu Y.-Y. Chan Y.-L. Leu C.-Y. Chern and C.-F. Chen Phytochemistry 1996 42 907. 168 Z.-Z. Ma Y. Hano T. Nomura and Y.-J. Chen Heterocycles 1997 46 541; (Chem. Abstr. 1998 128 292714). 169 Y.-C. Shen C.-C. Chein P.-W. Hsieh and C.-Y. Dub Taiwan Shuichan Xuehuikan 1997 24 117; (Chem. Abstr. 1997 127 357119). 170 M. Alvarez M. A. Bros and J. A. Joule Tetrahedron Lett. 1998 39 679. 171 Y. Kitahara H. Onikura Y. Shibano S. Watanabe Y. Mikami and A. Kubo Tetrahedron 1997 53 6001. 172 Y. Kitahara F. Tamura and A. Kubo Tetrahedron Lett. 1997 38 4441.173 C. J. Smith D. A. Venables C. Hopemann C. E. Salomon J. Jompa A. Takir J. Faulkner and C. M. Ireland J. Nat. Prod. 1997 60 1048. 174 P. W. Ford and D. S. Davidson J. Nat. Prod. 1997 60 1051. 175 Y. Kitahara S. Nakahara T. Yonezawa M. Nagatsu Y. Shibano and A. Kubo Tetrahedron 1997 53 17029. 176 C. Elder P. Schupp P. Proksch V. Wray K. Steube C. E. Muller W. Frobenius M. Herderich and R. W. M. Soest J. Nat. Prod. 1998 61 301. 177 M. Varaoglu T. H. Corbett F. A. Vocleriote and P. Crews J. Org. Chem. 1997 62 7078. 178 K.-I. Kimura Y. Ikeda S. Kagami H. Takahashi K. Takahashi M. Ubukata and K. Isono PCT Int. Appl. WO 9741248; (Chem. Abstr. 1998 128 2974). 179 R. J. Capon F. Rooney L. M. Murray E. Collins A. T. R. Sim J. A. P.Rostas M. S. Butler and A. R. Carroll J. Nat. Prod. 1998 61 660. 180 S. D. Sarker L. Dinan V. Sik E. Underwood and P. G. Watermann Tetrahedron Lett. 1998 39 1421. 181 K. Torigoe S. Nakajima H. Suzuki M. Nagashima K. Ojiri and H. Suda Jpn. Kokai Tokkyo Koho 09227587; (Chem. Abstr. 1997 127 184 A. Zampella M. V. D’Auria L. Minale C. Debitus and C. Roussakis 261794). 182 A. Zampella M. V. D’Auria L. Minale and C. Debitus Tetrahedron 1997 53 3243. 183 R. R. West J. Van Ness A.-M. Varming B. Rassing S. Briggs S. Gasper P. A. Mackernan and J. Piggot J. Antibiot. 1996 49 967; (Chem. Abstr. 1997 126 28911). J. Am. Chem. Soc. 1996 118 11085. 185 A. D. Patel A. J. Freyer P. Offen M. F. Bean and R. K. Johnson J. Nat. Prod. 1997 60 704. 83 Nat. Prod.Rep. 2000 17 57–84 186 H. Iziumida K. Adachi A. Mihara T. Yasuzawa and H. Sano J. Antibiot. 1997 50 916; (Chem Abstr. 1998 128 72714). 187 B. Moon B. J. Baker and J. B. McClintock J. Nat. Prod. 1998 61 116. 188 H. Onodera M. Satake Y. Oshima T. Yasumoto and W. N. Carmichael Nat. Toxins 1997 5 146; (Chem Abstr. 1998 128 86289). 189 T. H. Hong D. R. Jimenez and T. F. Molinski J. Nat. Prod. 1998 61 158. 190 T. Jahn G. M. Konig A. D. Wright G. Worheide and J. Reitner Tetrahedron Lett. 1997 38 3883. 191 J. Kobayashi M. Suzuki and M. Tsuda Tetrahedron 1997 53 15681. 192 T. Kawauchi T. Sasaki K.-I. Yoshida H. Matsumoto R.-X. Chen and M. Y. Huang J. Antibiot 1997 50 297; (Chem Abstr. 1997 127 31287). 193 A. Furstner and H. Weintritt J. Am. Chem. Soc. 1998 120 2817. 194 M. Yoshikawa T. Murakami M. Johji and H. Matsuda Heterocycles 1997 46 301; (Chem Abstr. 1998 128 268205) Nat. Prod. Rep. 2000 17 57–84 84 195 M. Kobayashi Y. Miyamoto S. Aoki N. Murakami I. Kitagawa Y. In and T. Ishida Heterocycles 1998 47 195; (Chem Abstr. 1998 128 321796). 196 Y. Guo E. Travellone G. Scognamiglio and G. Ciminoi Tetrahedron Lett. 1998 39 463. 197 X. Wu G. Qin K. K. Cheung and K. F. Cheng Tetrahedron 1997 53 13323. 198 H. Osada S. L. Choi H. Kakeya K. Isono and F. Yamashita Jpn. Kokai. Tokyo. Koho 09255680; (Chem Abstr. 1997 127 261790). 199 Y. Aotani H. Nagata and M. Yoshida J. Antibiot. 1997 50 543; (Chem Abstr. 1997 127 217522). 200 F. Kong E. I. Graziani and R. J. Anderson J. Nat. Prod. 1998 61 267. 201 J. Kobayashi D. Watanabe N. Kawasaki and M. Tsuda J. Org. Chem. 1997 62 9236. 202 J. D. Winkler and J. M. Axten J. Am. Chem. Soc. 1998 120 6425. Review a809403i

ISSN:0265-0568    

DOI:10.1039/a809403i

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Lysine biosynthesis and metabolism in fungi T. Mark Zabriskie* and Michael D. Jackson College of Pharmacy Oregon State University Corvallis OR 97331 USA Received (in Cambridge) 15th July 1999 Covering 1985–April 1999 Role of a-aminoadipate pathway intermediates in 6 1 Introduction lysine biosynthesis 1.1 The a-aminoadipate pathway to l-lysine 2 Enzymes of the a-aminoadipate pathway 2.1 Homocitrate synthase 2.2 Homoaconitate hydratase 2.3 Homoisocitrate dehydrogenase 2.4 a-Aminoadipate aminotransferase 2.5 a-Aminoadipate reductase 2.6 Saccharopine reductase 2.7 Saccharopine dehydrogenase 345 Role of pipecolic acid in lysine biosynthesis Lysine catabolism secondary metabolism The a-aminoadipate pathway in archaea and bacteria Conclusion Acknowledgements References 789 1 Introduction lysine biosynthesis Among the 20 common proteinogenic amino acids L-lysine is unusual in that two diverse pathways have evolved for its biosynthesis.In bacteria lower fungi (some Phycomycetes) and green plants l-lysine is synthesized via the diaminopimelate Mark Zabriskie was born in Salt Lake City in 1960. He attended the University of Utah where he received his Bachelors Degree in Chemistry in 1985. Continuing at Utah he studied marine natural products chemistry with Prof Chris Ireland and obtained a PhD in Medicinal Chemistry. In 1989 he began a postdoctoral fellowship at the University of Alberta working with Prof John Vederas on the mechanism and inhibition of peptide amide hormone formation.He joined the medicinal chemistry faculty of the College of Pharmacy at Oregon State University in 1992 where he now holds the rank of Associate Professor and is also a faculty member of the Center for Gene Research and Biotechnology and the program in Molecular and Cellular Biology. His research interests center on primary and secondary metabolism of amino acids with particular focus on transformations of lysine and arginine. His group is also involved in studying the molecular genetics and enzymology of nonribosomal peptide biosynthesis. Dr Zabriskie lives in Corvallis Oregon with his wife and their two sons with whom he enjoys mountain sports travel and baseball. This journal is © The Royal Society of Chemistry 2000 pathway in seven steps starting with aspartate semialdehyde and pyruvate.In addition to the lysine required for protein biosynthesis this pathway is the source of the diaminopimelate (DAP) and lysine incorporated into bacterial cell wall peptidoglycan. The pivotal role that enzymes of the DAP pathway play in cell viability fuelled extensive investigation into targeting these enzymes for the development of new antibacterial agents and the area has been recently reviewed.1,2 Likewise the molecular genetics of the bacterial diaminopimelate pathway has received a great deal of attention. With the recent finding that the argD-encoded N-acetylornithine aminotransferase also exhibits N-succinyl-l,l-diaminopimelate+a-ketoglutarate aminotransferase (DapC) activity all the genes in the DAP pathway have been cloned.2,3 In Euglenoids and higher fungi (Ascomycetes and Basidomycetes) de novo l-lysine biosynthesis proceeds through the intermediacy of l-a-aminoadipate in a series of transformations entirely unrelated to the bacterial diaminopimelate route.Work with auxotrophic mutants during the 1950’s and 60’s established the identity of the intermediates in the pathway and characterization of the biochemical steps proceeded simultaneously. Most of the biochemical and genetic understanding of the pathway results from studies with the yeast Saccharomyces cerevisiae. Significant findings also stemmed from work with Yarrowia lipolytica Neurospora crassa and some Candida species. Research in the aminoadipate pathway area has witnessed a recent resurgence in activity due to in a large part heightened efforts in cloning and characterizing fungal genes.The availability of these genes has facilitated a number of significant advances in recent years. Several important insights Michael D. Jackson was born in Ogden Utah in 1968. He studied both chemistry and biology at Western Oregon State College and became interested in doing graduate work at the interface between chemistry and biology. During his undergraduate studies he received a WOSC/Teledyne Wah Chang internship in analytical chemistry. Michael entered the graduate program in the Chemistry Department at Oregon State University in 1992 where he worked initially with Dr Steven J.Gould and later joined Dr Mark Zabriskie’s group in the College of Pharmacy. His graduate work entails studying arginine secondary metabolism in the antibiotic-producing soil bacteria Streptomyces lavendulae and S. capreolus. Upon completing his PhD in late 1999 he will join the laboratory of Dr John M. Denu at Oregon Health Sciences University as a postdoctoral fellow working on the mechanism of protein phosphatases. When not busy with his research Michael likes spending time in the great outdoors golfing and building remote-controlled airplanes. 85 Nat. Prod. Rep. 2000 17 85–97 into catalytic and regulatory mechanisms in the pathway are directly attributed to leads identified through sequence homology with other genes in the databases.The main purpose of this review is to provide an overview of the aminoadipate pathway for lysine biosynthesis in fungi and present the properties of the individual enzymes and associated genes. The reader is referred to an excellent review for coverage of progress in the field prior to 1985.4 Bhattacharjee has more recently published an overview of the aminoadipate pathway with special consideration of the evolutionary features.5 Where relevant direct reference to the older literature will be cited. Different ways of designating genes appear in the lysine molecular genetics literature. Because this overview is not targeted towards genetics specialists a common representation will be used here in order to prevent confusion. Mutants are identified by lower case letters in italics (e.g.lys1) genes are denoted by upper case italic letters (e.g. LYS1) and gene products are symbolized by the same three letters as the gene with only the first letter capitalized (e.g. Lys1). Another area of potential confusion arises in instances where genes encoding the same enzyme in different organisms will have different names. Table 1 correlates each enzyme of the pathway with the various genes and organisms. Table 1 Correlation of enzymes of the a-aminoadipate pathway with the respective genes and producing organisms Enzyme Homocitrate synthase Homoaconitate hydratase Homoisocitrate dehydrogenase a-Aminoadipate aminotransferase a-Aminoadipate reductase Saccharopine reductase Saccharopine dehydrogenase Scheme 1 Enzymes of the fungal a-aminoadipate pathway to lysine i homocitrate synthase EC 4.1.3.21; ii & iii homoaconitase EC 4.2.1.36; iv homoisocitrate dehydrogenase EC 1.1.1.87; v aminoadipate aminotransferase EC 2.6.1.39; vi aminoadipate reductase EC 1.2.1.31; vii saccharopine reductase EC 1.5.1.10; viii saccharopine dehydrogenase EC 1.5.1.7.Nat. Prod. Rep. 2000 17 85–97 86 Yeast/Fungus Gene S. cerevisiae Y. lipolytica P. chrysogenum S. cerevisiae A. nidulans LYS20 LYS1 LYS1 LYS4 LYSF S. cerevisiae S. pombe C. albicans P. chrysogenum S. cerevisiae S. cerevisiae Y. lipolytica C. albicans LYS2 LYS1 LYS2 LYS2 LYS9 LYS1 LYS5 LYS1 1.1 The a-aminoadipate pathway to l-lysine Lysine biosynthesis in fungi requires eight steps involving seven free intermediates.Several steps involve transient or enzyme-bound intermediates and some transformations require the action of two gene products. The overall process is detailed in Scheme 1. Steps comprising the first half of the pathway leading to a-aminoadipate take place in the mitochondria; the exception being the synthesis of homocitrate in the nucleus. The latter steps converting a-aminoadipate to l-lysine are carried out in the cytoplasm. The first half of the aminoadipate pathway shares many similarities with the tricarboxylic acid (TCA) cycle; the early intermediates in the lysine pathway are simply one carbon higher homologs. As such the enzymology of much of the aminoadipate pathway is quite similar to that found in the TCA cycle.Fungal lysine biosynthesis begins with the condensation of aketoglutarate (1) and acetyl-CoA catalyzed by homocitrate synthase. The resulting homocitric acid (2) undergoes a dehydration yielding cis-homoaconitic acid (3) which in turn is converted to homoisocitric acid (4) by homoaconitase. Oxidation of 4 by homoisocitrate dehydrogenase results in the transient formation of oxaloglutarate followed by loss of carbon dioxide to yield a-ketoadipic acid (5). Glutamate-dependent transamination of a-ketoadipate by aminoadipate aminotransferase gives rise to l-a-aminoadipic acid (6). The second half of the pathway begins with the reduction of the side chain carboxy of 6 to form l-a-aminoadipic acid-d-semialdehyde (7) by aminoadipate reductase in a process requiring ATP and NADPH.Saccharopine reductase then catalyzes the condensation of 7 with l-glutamate and subsequent reduction of the imine to give l-saccharopine (8). The last step in the pathway is the cleavage of the carbon–nitrogen bond within the glutamate moiety of 8 carried out by saccharopine dehydrogenase. The final products are l-lysine (9) and a-ketoglutarate (1). 2 Enzymes of the a-aminoadipate pathway 2.1 Homocitrate synthase The condensation of one molecule of acetyl CoA with aketoglutarate to form homocitrate catalyzed by homocitrate synthase (acetyl-CoA+2-ketoglutarate C-acetyl transferase; EC 4.1.3.21) represents the first committed step of fungal lysine biosynthesis (Scheme 2).Enyzmatic formation of homocitrate in Saccharomyces cerevisiae was first reported in 1964.6 It was later demonstrated that two homocitrate synthase isozymes could be separated by isoelectric focussing.7 Both isozymes were inhibited by lysine but only one form was transcriptionally repressed when the yeast was grown in medium supplemented with lysine.8 Scheme 2 An early subcellular localization study reported that 80% of the total homocitrate synthase activity in a S. cerevisiae cell lysate resided in the particulate fraction and was presumed to be associated with the mitochondria. It was not determined if the observed activity was due to both isozymes.9 This report also suggested that an observed inhibition of homocitrate synthase by low concentrations of coenzyme-A could be a regulatory mechanism.A more recent investigation into the subcellular forms of homocitrate synthase in the penicillin G producer Penicillium chrysogenum Q176 found the mitochondrial enzyme to be highly unstable whereas the cytosolic form could be purified 500-fold to near homogeneity.10 The cytosolic isozyme exhibited a native molecular mass of 155 kDa by gel filtration chromatography and a subunit size of 54 kDa by SDSPAGE. Contrary to findings in S. cerevisiae 75% of the total enzyme activity was located in the cytosol and no inhibition by coenyzme-A was observed. During the sequencing of chromosome IV from S. cerevisiae an open reading frame (ORF D1298) was identified that shared significant sequence similarity with the NIFV gene of Azotobacter vinelandii and a-isopropylmalate isomerase an enzyme involved in leucine biosynthesis.11 NifV catalyzes the formation of homocitrate not as a precursor to lysine but rather as an element of the iron–molybdenum cofactor in nitrogenase.This cofactor is composed of a Fe7S9Mo metal sulfur core and one molecule of homocitrate. Because S. cerevisiae has no known ability to fix nitrogen ORF D1298 is presumed to encode a homocitrate synthase functioning in lysine biosynthesis. Disruption of this gene named LYS20 in S. cerevisiae resulted in transformants exhibiting a three-fold decrease in homocitrate synthase activity.12 The failure to completely eliminate homocitrate formation by disrupting a single gene is consistent with earlier findings of two homocitrate synthase isozymes in this organism.Because the N-terminus of the predicted amino acid sequence contained no mitochondrial targeting sequence it was proposed that Lys20 is cytosolic. Expression of the homocitrate synthase isoform encoded by LYS20 was shown to be repressed by lysine. Using monoclonal antibodies against nuclear proteins from S. cerevisiae Chen et al. made the surprising discovery that two isozymes of homocitrate synthase are localized in the nucleus.13 Immunoscreening a yeast expression library allowed identification of two ORFs from chromosome IV corresponding to YDL182w (LYS20) and YDL131w in the S. cerevisiae database. LYS20 and YDL131w were shown to direct the expression of 47 and 49 kDa proteins respectively.The sequence of the YDL131w product is predicted to be 90% identical to Lys20. Localization of the proteins to the nucleus was based upon cell and nuclear fractionation and immunofluorescence studies. This finding was quite unexpected given the number of earlier reports that identified homocitrate synthase activity in the mitochondria and cytoplasm. While most of the homocitrate synthase was localized to the nucleus the remainder could account for the activity detected elsewhere in the cell. Furthermore it was suggested that crudely prepared mitochondria fractions may have contained nuclear fragments. The LYS1 gene encoding homocitrate synthase has been cloned and sequenced from the yeast Yarrowia lipolytica.14 Northern blot analyses indicate a single homocitrate synthase transcript is produced and Southern hybridization revealed a single copy of the gene is found in this species.The Y. lipolytica LYS1 is predicted to encode a 446 residue protein (48 kDa) possessing 84% identity at the amino acid level with the predicted sequence of S. cerevisiae Lys20. Deletion of Y. lipolytica chromosomal LYS1 produced lysine auxotrophs that regained lysine independent growth when further transformed with a self-replicating plasmid carrying LYS1. The LYS1 gene from P. chrysogenum was recently cloned and shown to be 71.1% and 71.7% similar in amino acid sequence with homocitrate synthases from Y. lipolytica and S. cerevisiae respectively.15 The gene codes for a 474 amino acid protein with an expected mass of 52 kDa.Expression of LYS1 was mildly repressed by high lysine concentrations in the growth medium and it was proposed that repression is a weak regulatory mechanism in comparison to lysine feedback inhibition of homocitrate synthase. 2.2 Homoaconitate hydratase In early studies on the aminoadipate pathway S. cerevisiae lys4 mutants were characterized that were auxotrophic for lysine accumulated homocitrate and cis-homoaconitate and lacked homoaconitate hydratase activity.16 Also identified were lys7 mutants which accumulated homocitrate and exhibited homocitrate synthase and homoaconitate hydratase activity. Based on these findings it was proposed that two distinct enzymes are needed for the conversion of homocitrate to homoisocitrate (Scheme 3).The enzymatic conversion of homoisocitrate to cis- Scheme 3 homoaconitate was first demonstrated in 1966 by following the formation of a chromophore at 240 nm.17 The transformation of cis-homoaconitate but not the trans-isomer to homoisocitrate by cell free extracts was also documented. The enzyme responsible for the activity homoaconitate hydratase (homoaconitase; EC 4.2.1.36) could be separated from the highly similar cis-aconitate hydratase by ammonium sulfate precipitation. Subsequent studies showed that cis-homoaconitate hydratase is a mitochondrial enzyme that is repressed by both lysine and glucose and established homoisocitrate as an intermediate in the biosynthesis of lysine and cis-homoaconitate as a potential intermediate.18 References to homocitrate dehydrase an enzyme proposed to form cis-homoaconitate from homocitrate appear in the literature but the activity has not been correlated with a purified protein.The two-step conversion of homocitrate to homoisocitrate is analogous to the aconitase reaction for the transformation of citrate to isocitrate in the TCA cycle. The reaction proceeds via enzyme bound cis-aconitate and is carried out by a single protein. Isopropylmalate isomerase catalyzes similar sequential elimination–addition reactions in the leucine biosynthetic 87 Nat. Prod. Rep. 2000 17 85–97 pathway. Thus while cis-homoaconitate can be detected in the cells and serves as a precursor to homoisocitrate the majority of cis-homoaconitate may be enzyme bound during the normal reaction.A small amount of free cis-aconitate is detectable in cells and in labeled form and it has been shown to serve as a precursor to isocitrate. The LYS4 gene was originally cloned by functional complementation on a 7.8 kb fragment of S. cerevisiae genomic DNA that also contained the linked LYS15 gene.19 When inserted into the YEp13 vector this fragment complemented lys4 lys15 and lys4lys15 mutations. Gamonet and Lauquin also cloned LYS4 and submitted the sequence of the homoaconitase gene to GenBank (accession X93502). Weidner et al. cloned the LYSF gene from the filamentous fungus Aspergillus nidulans and showed it encodes homoaconitase.20 The gene is 2397 bp in size contains a single 72 bp intron and the ORF encodes a 775 amino acid protein of approximately 84 kDa.Growing A. nidulans in the presence of lysine decreased homoaconitase specific activity by six-fold suggesting regulation by lysine. The A. nidulans enzyme exhibits 55% sequence identity at the amino acid level with S. cerevisiae homoaconitase. The greatest similarity is seen in regions containing cysteines believed to be involved in forming an Fe–S cluster analogous to that found in aconitase. Both the A. nidulans and S. cerevisiae homoaconitases share only 20% similarity with S. cerevisiae aconitase.20,21 A sequence analysis study of homoaconitase and members of the aconitase-family proteins appeared that explores the evolutionary relationship of the enzyme from the lysine biosynthetic pathway with aconitase isopropylmalate isomerase and iron-responsive element binding proteins from eukaryotes archaea and eubacteria.22 Sequence similarities are found primarily in residues associated with the Fe4–S4 cluster and the findings are proposed to provide an evolutionary link between genes found in the aminoadipate pathway and organisms other than fungi.It was suggested that homoaconitase be added to the aconitase-family proteins. As mentioned above lys7 mutants accumulate homocitrate while exhibiting homocitrate synthase and homoaconitate hydratase activity. This was interpreted as evidence that LYS7 may code for a homocitrate dehydrase. The S. cerevisiae LYS7 gene has now been cloned and is predicted to encode a unique 249 amino acid protein.23 Transcription was not regulated by lysine-specific or general amino acid control mechanisms and mutants lacking the entire LYS7 gene displayed phenotypes including pH and temperature sensitivity in addition to requiring lysine for growth.The multiple phenotypes observed in LYS7 null mutants and the constitutive expression pattern suggested that the gene product does not have a role confined to lysine biosynthesis. Insight into the actual role of Lys7 came from studies on copper trafficking in yeast. Culotta et al. identified Lys7 as a Cu–Zn superoxide dismutase-specific copper chaperone.24 S. cerevisiae mutants lacking the LYS7 gene had normal amounts of Cu–Zn superoxide dismutase (SOD1) but lacked enzyme activity.When 64Cu was used to label SOD1 in wild-type yeast a single radioactive band was detected. The lys7 null mutants were not radiolabeled with 64Cu but the defect could be complemented by the human copper chaperone for SOD1. Gamonet et al. observed similar results in their work with lys7 mutants.21 S. cerevisiae mutants in which LYS7 had been deleted were auxotrophic for lysine and methionine sensitive to oxygen- and superoxide-generating agents and light irradiation. 21 The latter finding suggests that Lys7 is involved in oxidative stress protection. Normal amounts of Cu–Zn superoxide dismutase (SOD1) were found but there was no detectable dismutase activity. Addition of Cu2+ to the growth medium of cell-free extracts restored enzyme activity.Subcellular localization revealed that the Lys7 is cytosolic and sequence analysis showed it possessed a metal-binding domain similar to other Cu-transporting ATPases. Stretches of the Lys7 sequence share Nat. Prod. Rep. 2000 17 85–97 88 similarity with the dimerization domains of superoxide dismutase but yeast two-hybrid screening failed to confirm an interaction between the two proteins. 2.3 Homoisocitrate dehydrogenase Homoisocitrate dehydrogenase (3-carboxy-2-hydroxyadipate dehydrogenase; EC 1.1.1.87) catalyzes the NAD+-dependent conversion of homoisocitrate to a-ketoadipate (Scheme 4) and Scheme 4 activity is monitored spectrophotometrically by following the reduction of NAD+ at 340 nm.25 The S.cerevisiae enzyme has been purified approximately 500-fold and has an estimated molecular mass of 48 kDa. The enzyme is separable from isocitrate dehydrogenase and has a KM for homoisocitrate of 10 mM a pH optimum of 8.5 for the oxidative decarboxylation of homoisocitrate and a pH optimum of 7.0 for the reductive carboxylation of a-ketoadipate. The Y. lipolytica dehydrogenase has been purified to electrophoretic homogeneity and appears as a single 48 kDa band under denaturing and nondenaturing conditions.26 Native molecular weight estimation by gel filtration revealed several peaks of activity between 49 and 90 kDa. Addition of homoisocitrate to the buffer caused most of the activity to elute at a volume corresponding to 90 kDa and indicates that native homoisocitrate dehydrogenase may function as a dimer.Two mutants lys9 and lys10 were identified which lacked homoisocitrate dehydrogenase activity. The lys9 mutant exhibited some carboxylating activity whereas the lys10 mutant retained NAD+-reducing activity. Other fungi in which homoisocitrate dehydrogenase activity has been detected include the pathogens Candida albicans Filobasidiella neoformans Aspergillus fumigatus and the fission yeast Schizosaccharomyces pombe.27 Levels of homoisocitrate dehydrogenase activity are repressed in S. cerevisiae 7305d (lys14) mutants whether grown in lysine-supplemented or minimal media.28 The activity is constitutively derepressed in lys9 mutants which are deficient in levels of saccharopine reductase.29 The relationship of lys9 and lys14 and the role of Lys14 in regulating lysine biosynthesis gene expression is discussed in Section 2.6.2.4 a-Aminoadipate aminotransferase a-Aminoadipate aminotransferase (EC 2.6.1.39) is a pyridoxal 5A-phosphate-requiring enzyme that catalyzes the l-glutamatedependent reversible formation of a-aminoadipate from aketoadipate (Scheme 5). a-Aminoadipic acid is a key branch Scheme 5 point metabolite that can enter into secondary metabolism leading to the b-lactam antibiotics in some fungi and actinomy-cetes or continue on in the biosynthesis of lysine. Aminotransferase activity has been identified in Torulopsis utilis N. crassa S. cerevisiae and a S. cerevisiae threonine auxotroph thr5.30,31 The majority of information on this step comes from early studies conducted by Matsuda and Ogur in S.cerevisiae. 32,33 The aminoadipate aminotransferase activity is associated with two isozymes that are separable by ion exchange and size exclusion column chromatography. a- Aminoadipate aminotransferase I has a molecular mass of 100 kDa is located in the mitochondria and is noncompetitively inhibited by a-ketoglutarate. This isozyme accepts either glutamate or aspartate as the amine source in the forward reaction but shows weak activity in the reverse direction wherein a-aminoadipate serves as amine donor. a-Aminoadipate aminotransferase II is a cytosolic enzyme with a molecular mass of 140 kDa and a strict requirement for glutamate as the amine source.Unlike a-aminoadipate aminotransferase I the forward reaction catalyzed by isozyme II is not inhibited by aketoglutarate. Neither enzyme was significantly affected by lysine. In analyzing the effect of media composition on enzyme activity a-aminoadipate aminotransferase II was found to be derepressed by a-aminoadipate and slightly repressed by glucose while a-aminoadipate aminotransferase I activity varied only slightly under different growth conditions. A kynurenine aminotransferase (EC 2.6.1.7) was isolated from the yeast Hansenula schneggii which had physical characteristics comparable to those of S. cerevisiae aminoadipate aminotransferase I and utilized a-aminoadipate as a modest alternate substrate.34 This enzyme is associated with tryptophan catabolism and catalyzes the transamination between l-kynurenine and a-ketoglutarate to form glutamate and kynurenic acid (Scheme 6).When a-ketoadipate is used as the amine acceptor activity is nearly identical to that observed with a-ketoglutarate. Scheme 6 Kynurenine and a-aminoadipate aminotransferase activities are well documented in mammalian systems and the reactions appear to be catalyzed by a number of different pyridoxal 5Aphosphate-dependent aminotransferases. Several studies suggested that kynurenine and a-aminoadipate aminotransferase activities are attributed to the same enzyme when efforts to separate the activities were unsuccessful. Mawal and Deshmukh provided evidence that the two activities in rat kidney are associated with two separate proteins whereas Buchli et al.cloned and expressed a soluble protein from the same tissue able to catalyze both reactions.35,36 Cloning of an a-aminoadipate aminotransferase gene solely associated with lysine biosynthesis in fungi remains to be reported. Taking this into consideration with the broad substrate specificity observed for several yeast aminotransferases suggests the transamination reaction converting a-ketoadipate to aaminoadipate may be conducted by an enzyme with dual functions. Aromatic aminotransferase I from S. cerevisiae has been suggested as possibly having such a role.37 This constitutively expressed form of aromatic aminotransferase is active not only with the aromatic amino acids but also with aaminoadipate methionine and leucine when phenylpyruvate is the amine acceptor.The action of aromatic aminotransferase I was reported to account for half of the glutamate:a-ketoadipate transaminase activity detected in cell-free extracts and the enzyme was suggested to be identical to one of the two known a-aminoadipate aminotransferases. Aromatic aminotransferase I has properties of a general aminotransferase which like several aminotransferases of E. coli may be able to play a role in several otherwise unrelated metabolic pathways. 2.5 a-Aminoadipate reductase Reduction of a-aminoadipate to the semialdehyde by aaminoadipate reductase (a-aminoadipate-d-semialdehyde dehydrogenase; EC 1.2.1.31) is arguably the most fascinating transformation in the fungal lysine biosynthetic pathway and is an entirely unique mechanism in primary metabolism (Scheme 7).It was reported as early as 1959 that the reduction Scheme 7 of a-aminoadipate required ATP Mg2+ NADPH and glutathione. Later work suggested that an adenylated intermediate is formed prior to reduction as opposed to the generation of a phosphate mixed anhydride which precedes carboxy reductions in proline and arginine biosynthesis. The activation of amino acid carboxy groups as acyladenylates is most commonly associated with the protein synthesis on ribosomes. It is also the means of activating carboxy groups utilized by nonribosomal peptide synthetases involved in secondary metabolism. Evidence that the reduction required two distinct gene products in S.cerevisiae was first reported by Bhattacharjee’s group in 1970.38 It was observed that both lys2 and lys5 mutants of S. cerevisiae lacked a-aminoadipate reductase activity. Subsequent in vitro studies using crude cell free extracts of lys2 and lys5 mutants revealed that reductase activity could be regained by complementation and established that LYS2 and LYS5 were unlinked structural genes.39 In the same study the S. cerevisiae a-aminoadipate reductase was partially purified and found to have an estimated Mr of 180 kDa based on calibrated gel-filtration analysis. The earliest mechanistic proposal for the reduction involved a process whereby the d-carboxy was activated as the adenylate in the first step thus facilitating hydride transfer from NADPH (Scheme 8).Decomposition of the hemiacetal in a third step Scheme 8 yields AMP and a-aminoadipic-d-semialdehyde (7). Support for this mechanism came from demonstrating an a-aminoadipate-dependent ATP–PPi exchange activity and from the observed accumulation of an adenylated a-aminoadipate derivative in a lysine auxotroph unable to grow on a-aminoadipate. 89 Nat. Prod. Rep. 2000 17 85–97 The original mechanistic proposal suggested the first two steps were catalyzed by Lys2 and the third step was catalyzed by Lys5.40 These gene products were proposed to form a heterodimeric multifunctional a-aminoadipate reductase. Wild-type S. cerevisiae cannot use a-aminoadipate as a sole nitrogen source whereas lys2 and lys5 mutants can.In fact growth of wild-type cells is inhibited by a-aminoadipate when the yeast is grown in a medium containing other amino acids as the primary nitrogen source. The mutant strains are able to use the exogenous a-aminoadipate as amine donor in the reversal of the normal a-aminoadipate aminotransferase reaction to yield l-glutamate which then serves as a more general nitrogen donor. Zaret and Sherman investigated why normal strains of S. cerevisiae were unable to use a-aminoadipate as a nitrogen source and found that high levels of 6 resulted in the accumulation of a toxic metabolite.41 The accumulated intermediate was not structurally characterized but was suggested to be the semialdehyde 7. They also demonstrated that the product did not accumulate in lys2 and lys5 mutants.Growth of lys9 mutants which are deficient in saccharopine reductase the enzyme that uses 7 as a substrate was inhibited to a greater extent by a-aminoadipate than that of wild-type cells. Growth of lys2lys9 and lys5lys9 double mutants was unaffected by aaminoadipate. Insight into the roles of the LYS2 and LYS5 gene products emerged with the cloning and sequencing of the respective genes. The high frequency of obtaining lys2 mutants coupled with the ease of positive selection using a-aminoadipate as the sole nitrogen source facilitated the cloning of LYS2 by functional complementation. The first reported cloning of LYS2 from S. cerevisiae appeared in 1983 and was followed shortly after by two other reports.42–44 The complete nucleotide sequence of S.cerevisiae LYS2 was reported in 1991 and showed the gene encoded a 1392 amino acid protein having a calculated molecular weight of 155 kDa.45 When the translated sequence of the LYS2 ORF was used to search the GenBank database for proteins with similar amino acid sequences Lys2 showed the greatest homology with the adenylation and thiolation domains of tyrocidine synthetase 1. This enzyme is the product of the Bacillus brevis tycA gene and a component of the nonribosomal peptide synthetase complex involved in the assembly of the peptide antibiotic tyrocidine.46 Nonribosomal peptide synthetases are multifunctional modular proteins that catalyze the sequence-specific condensation of amino acids into peptides without involvement of a nucleic acid template.The ATP-dependent activation of the amino acid carboxy group results in the formation of an amino acyladenylate. This prepares the amino acid for transfer to the thiol group of a 4A-phosphopantetheine (Ppant) cofactor to form a covalent thioester intermediate. The Ppant cofactor is covalently attached to a strictly conserved serine in the thiolation domain of the enzyme. At this stage the amino acid may be structurally modified (e.g. epimerized or N-methylated) or condense to form a peptide bond with an amino acid on an adjacent module which has been similarly activated and attached to the peptide synthetase. During studies on the biosynthesis of saframycin Mx1 in the myxobacterium Myxococcus xanthus Pospiech et al.identified a peptide synthetase ORF (SafA2) coding for two amino acid activation modules one of which is followed by a 370 amino acid region exhibiting 33% identity to the carboxy terminus of S. cerevisiae Lys2.47 The region is similar to ketoreductase domains associated with polyketide synthases and possesses a characteristic sequence motif for a NAD(P)H binding site. This represented the first report of an oxidoreductase domain associated within a peptide synthetase module. The LYS5 gene was subsequently cloned by Borell and Bhattacharjee in 1988 by functional complementation of a S. cerevisiae lys5 mutant.48 The gene was contained on a 7.5 kb DNA fragment and shown by restriction analysis to have no Nat. Prod. Rep.2000 17 85–97 90 homology with LYS2. Further subcloning established that the LYS5 gene could not be any greater than 1.65 kb.49 Hence the encoded protein must be significantly smaller than the 155 kDa LYS2 product. In 1996 the complete nucleotide sequence of the S. cerevisiae LYS5 gene was determined and predicted to encode a 272 amino acid 31 kDa protein.50 In combination with the 155 kDa Lys2 protein this was viewed as supporting evidence of a 180 kDa heterodimeric reductase. Database searching at the time failed to identify any proteins with significant homology to Lys5. The fission yeast S. pombe also requires two distinct genes for the ATP-dependent reduction of a-aminoadipate. The S. pombe LYS1 and LYS7 genes correspond to S. cerevisiae LYS2 and LYS5 respectively.The LYS1 gene was cloned and partially characterized and the predicted amino acid sequence from a fragment of the gene was found to share 49% amino acid sequence identity with the amino terminal region of S. cerevisiae Lys2.51 More recently the S. pombe LYS1 gene has been shown to encode a 1415 residue protein with a calculated molecular weight of 155.8 kDa.52 Analysis of the deduced amino acid sequence of S. pombe Lys1 revealed a 52% overall identity to S. cerevisiae Lys2 and a strong homology to peptide synthetases including ACV synthetases from P. chrysogenum and A. nidulans. ACV synthetase adenylates the d-carboxylate of a-aminoadipate in the process of forming the tripeptide d-(la-aminoadipyl)-l-cysteinyl-D-valine (ACV) the linear precursor to the penicillins and cephalosporins (Scheme 9).Scheme 9 Initial steps of penicillin biosynthesis assembly of the primary amino acid precursors into ACV and conversion to isopenicillin N. A 4.8 kb fragment of C. albicans DNA able to complement lys2 mutants of both C. albicans and S. cerevisiae has been cloned and characterized.53 Sequence analysis of this DNA fragment revealed an ORF corresponding to a 1391 residue protein with an estimated Mr of 154 kDa. This C. albicans LYS2 ORF showed 63% identity to the corresponding S. cerevisiae gene at the nucleotide level. Analysis of the deduced amino acid sequence revealed regions with a high level of similarity to ACV synthetases from several species and a region toward the C-terminus similar to a signature sequence found in short chain alcohol dehydrogenases.The study reporting the cloning of C. albicans LYS2 also provided insight into the repression of gene transcription and regulation of a-aminoadipate reductase activity by lysine. Northern analysis of mRNA levels in cells grown in minimal medium showed that transcription of LYS2 is substantially depressed when the medium is supplemented with lysine. When the cells were grown in a rich medium the LYS2 mRNA could not be detected suggesting the gene is under general amino acid control and also regulated to a certain degree by lysine. The same trend was observed for a-aminoadipate reductase activity. Enzyme activity in cells grown in minimal medium supplemented with lysine was 40% lower and that from cells grown in rich medium was 66% lower compared to cells grown in minimal medium.Lysine also causes feedback inhibition of a-aminoadipate reductase. Addition of 50 mM lysine to assay mixtures reduced a-aminoadipate reductase activity by 70% and a 1 mM concentration of the lysine analog (S)-2-aminoethyl-l-cysteine reduced activity by 92%. The P. chrysogenum LYS2 gene has also been cloned and characterized.54 The gene codes for a 1409 residue protein and exhibits 49.9% identity to the S. cerevisiae gene and 51.3% and 48.1% identity to the S. pombe and C. albicans a-aminoadipate reductase genes respectively. When compared with the aaminoadipate activating region of ACV synthetase a modest 12.4% identity at the amino acid level was observed.The P. chrysogenum LYS2 gene is located on chromosome III in strain AS-P-78 and on chromosome IV in strain P2 whereas the penicillin biosynthetic gene cluster is located on chromosome I in both strains. This is consistent with evidence that the aminoadipate pool required for penicillin production originates from lysine degradation rather than from the pool generated during lysine biosynthesis.55 A 160 kDa a-aminoadipate reductase has been partially characterized from Candida maltosa and exhibits properties similar to those observed for the enzyme from S. cerevisiae.56 A subsequent report by the same group revealed that C. maltosa mutants deficient in a-aminoadipate reductase activity could have the activity partially restored by transformation with plasmids carrying S.cerevisiae LYS2.57 The partial (8–22%) recovery of activity was attributed to unstable plasmids rapid degradation of S. cerevisiae Lys2 weak transcription of the S. cerevisiae gene and/or incorrect processing. With the finding that Lys2 must be post-translationally modified by Lys5 (see below) the latter explanation may include S. cerevisiae Lys2 serving only as a poor substrate for C. maltosa Lys5. In 1996 Lambalot et al. described a new enzyme family involved in the post-translational modification of enzymes requiring a covalent Ppant cofactor.58 These phosphopantetheinyl transferases (PPTases) catalyze the transfer of the 4Aphosphopantetheine moiety from coenzyme A to a conserved serine residue found in all peptidyl carrier protein (PCP) domains of nonribosomal peptide synthetases.Similar PPTases are involved in cofactor attachment to the acyl carrier domains of polyketide synthases thereby converting the inactive apo form of the enzyme to the active holo form. Sequence homology searching revealed that Lys5 showed a strong similarity to members of this newly described family of enzymes and the proposal was made that Lys5 promoted the phosphopantetheinylation of Lys2 and that Lys2 carries out both the adenylation and reduction of the a-aminoadipate side chain carboxy. Very recently Walsh and co-workers further dissected the relationship of Lys2 and Lys5.59 Sequence analysis of Lys2 revealed three functional domains; a 60 kDa peptide synthetaselike adenylation (A) domain (residues 225–808) a 14 kDa peptidyl carrier protein (PCP) domain (residues 809–924) and the reductase (R) domain (amino acids 925–1392).The first 224 residues of the protein may constitute a fourth domain but this region has not been assigned a function. Recombinant Lys5 Lys2 and truncated fragments of Lys2 were all overproduced in E. coli and used to assess the function of Lys5 and the roles of the A PCP and R domains. Using autoradiography and mass spectrometry Lys5 was shown to be capable of transferring [3H]coenzyme A to the 14 kDa Lys2-PCP domain. To obtain evidence that the Lys2 A domain adenylates a-aminoadipate a 105 kDa Lys2 A/PCP fragment was used in ATP–[32P]PPi exchange assays. This truncated Lys2 catalyzed the l-aaminoadipate-dependent incorporation of [32P]PPi into ATP whereas D-a-aminoadipate and the homologs DL-diaminopimelate and l-glutamate were poor substrates or produced no exchange activity.The aminoadipate analog (S)-carboxymethyl-l-cysteine served as a modest alternate substrate for the adenylation reaction and was used to demonstrate the formation of a covalent thioester intermediate. Thus incubation of [35S]- (S)-carboxymethyl-l-cysteine with Lys2 A/PCP followed by protein precipitation resulted in the association of 35S with the protein. Covalent radiolabeling could also be demonstrated by autoradiography after gel electrophoresis. However when [35S](S)-carboxymethyl-l-cysteine was incubated with holo- Lys2 followed by NADPH addition and protein precipitation the 35S was no longer associated with the protein thus illustrating a unique function for the reductase domain.Most enzymes employing covalent thioester intermediates release an acid product resulting from hydrolysis of the thioester. Alternately an intramolecular nucleophile such as an amine or hydroxy can attack the thioester and result in the release of a lactam or lactone respectively (e.g. cyclic peptides and depsipeptides). In the case of a-aminoadipate reductase reduction of the thioester yields a thiohemiacetal that decomposes to release the aldehyde. Hence LYS2 is the gene coding for apo-a-aminoadipate reductase and LYS5 encodes the requisite Lys2-PPTase. The overall process is outlined in Scheme 10.The extensive investigation of this step in lysine biosynthesis is in part due to the novel mechanism and also because of the usefulness of LYS2 as a tool for genetic studies. Because lys2 mutants require exogenous lysine for growth this property serves as a useful selection marker to identify strains possessing a wild-type gene. Furthermore lys2 mutants can be identified by their ability to grow on synthetic media having aaminoadipate as the sole nitrogen source. This ability to select for and against a given yeast gene is a trait shared only with the URA3 gene involved in uracil biosynthesis. The LYS2 gene has been used in this capacity in the construction of both replicating and integrative yeast transformation vectors.42–44 2.6 Saccharopine reductase Saccharopine reductase [saccharopine dehydrogenase (NADP+ l-glutamate forming) EC 1.5.1.10] catalyzes the condensation of a-aminoadipate-d-semialdehyde with l-glutamate and in the presence of NADPH produces l-saccharopine the penultimate product of the aminoadipate pathway (Scheme 11).Saccharopine reductase has been purified to near homogeneity from S. cerevisiae and shown to be a monomer of approximately 50 kDa.60 The reaction is reversible with the forward direction being favored at physiological pH. Because the semialdehyde is not readily available the enzyme is typically assayed in the reverse direction at pH 9.5 using saccharopine and NAD+ or NADP+ as substrates. The KMs for saccharopine and NAD+ were estimated at 2.3 mM and 0.05 mM respectively.Saccharopine formation in S. cerevisiae also requires the products of two unlinked genes LYS9 and LYS14.61 Both lys14 and lys9 mutants accumulate a-aminoadipate-d-semialdehyde and lack significant levels of saccharopine reductase. Hence it was concluded that Lys9 and Lys14 were both necessary for the biosynthesis of saccharopine reductase in wild-type cells. S. cerevisiae lys9 mutants are auxotrophic for lysine and do not exhibit significant saccharopine reductase activity whereas lys14 mutants grow slowly on media lacking lysine and retain low levels of reductase activity.62 The introduction of a plasmid carrying LYS9 into a lys14 mutant restored the saccharopine reductase activity to wild-type levels and conferred the ability to grow on minimal media.However the introduction of a plasmid harboring the LYS14 gene into a lys9 mutant did not complement the mutation and indicates that LYS9 is a structural protein and Lys14 is required for the expression of LYS9. Northern analysis to quantitate LYS9 mRNA in a lys14 mutant supports 91 Nat. Prod. Rep. 2000 17 85–97 Scheme 10 Illustrated summary of the proposed roles of Lys2 and Lys5 in the activation and reduction of a-aminoadipic acid. Scheme 11 this conclusion. In addition to the identification of a regulatory role for Lys14 a-aminoadipate-d-semialdehyde was found to serve as a coinducer of transcriptional activation. Low levels of saccharopine reductase activity in lys14 mutants can be explained by weak expression of LYS9 in the absence of induction by the semialdehyde.2.7 Saccharopine dehydrogenase The final step of the lysine biosynthetic pathway in fungi is the cleavage of saccharopine to yield a-ketoglutarate and l-lysine (Scheme 12). The NAD+-dependent oxidation is catalyzed by Scheme 12 saccharopine dehydrogenase (NAD+ l-lysine forming); EC 1.5.1.7. Fujioka and co-workers conducted extensive studies on S. cerevisiae saccharopine dehydrogenase during the 1970’s and early 1980’s. Their work revealed saccharopine dehydrogenase is a basic protein (isoelectric pH = 10.1) that exists as a 39 kDa monomer containing a single active site.63 The oxidation is reversible with the reaction yielding lysine exhibiting a maximum rate at pH 10 while the reverse reaction is favored at pH 7.The KMs for saccharopine and NAD+ were estimated to be 1.7 mM and 0.1 mM respectively. When measuring saccharopine formation the Michaelis constants for lysine a-ketoglutarate and NADH were determined to be 2.0 mM 0.55 mM and 0.089 mM respectively. A mechanism for the catalytic reaction based on initial rate pH studies and product/dead end inhibition studies has been proposed to involve initial oxidation to an iminium ion followed by addition of water to give the hemiaminal which cleaves to products.64 The reaction appears to follow a Bi-Ter mechanism in which Nat. Prod. Rep. 2000 17 85–97 92 binding of NAD+ precedes that of saccharopine. Lysine is the first product released followed by a-ketoglutarate and then NADH.65 Fujioka and Takata showed that the dehydrogenase catalyzes the stereospecific transfer of the hydrogen on C-2 of the saccharopine glutaryl moiety to the pro-R position at C-4 of NAD+.66 A search for alternate substrates of the S.cerevisiae dehydrogenase revealed a very high degree of substrate specificity. The only a-ketoacid evaluated that was able to substitute for a-ketoglutarate in the reverse reaction was pyruvate.67 A series of chemical modification experiments revealed that the active site of the enzyme possesses essential histidine,68 lysine,69 arginine,70 and cysteine71 residues. An eleven amino acid peptide containing the cysteine residue necessary for catalysis has been isolated and sequenced.72 The LYS1 gene encoding the S.cerevisiae dehydrogenase was cloned during studies on the regulatory role of LYS14 and the sequence deposited in GenBank (accession X77632).62 The corresponding gene has also been cloned from a number of other yeasts. In Y. lipolytica the LYS5 gene was cloned by complementation and shown to encode saccharopine dehydrogenase. 73 A single 1.5 kb RNA transcript was identified that hybridized with an internal fragment of LYS5 consistent with the 40 kDa molecular weight of the enzyme. Subsequent sequencing of a 2.5 kb DNA fragment complementing lys5 mutants of Y. lipolytica revealed two completely overlapping antiparallel ORFs. Site-directed mutagenesis studies and gene fusion experiments addressing the transcription and translation of the two ORFs established that ORF2 encodes saccharopine dehydrogenase.A function for the ORF1 product is unknown although the possibility that the RNA serves as an antisense regulator of ORF2 expression similar to situations found in prokaryotes was suggested. In N. crassa lys4 mutants are auxotrophic for lysine do not exhibit saccharopine dehydrogenase activity and accumulate saccharopine.74 Similar observations are seen in S. pombe lys3 mutants75 and C. albicans lys1 mutants.76 The cloned LYS1 gene from C. albicans has been localized to a 1.8 kb EcoR V-EcoR I restriction fragment. Transformation of C. albicans or S. cerevisiae lys1 mutants with plasmids harboring this DNA fragment results in prototrophs having significant saccharopine dehydrogenase activity.76 Following up on their earlier work with C.albicans Garrad et al. sequenced a DNA fragment carrying the LYS1 gene and showed it contains a 1.1 kb ORF encoding a 382 amino acid protein.77 C. albicans LYS1 exhibits 60% and 69% similarity at the nucleotide level with Y. lipolytica LYS5 and S. cerevisiae LYS1 respectively. C. albicans lysine auxotrophs are nonpathogenic in experimental infections in mice.78 Because the uniqueness of the saccharopine structure may lead to target specificity inhibition of saccharopine dehydrogenase might be a viable means of controlling opportunistic fungal pathogens. To test this hypothesis amide analogs of saccharopine (Fig. 1) were prepared and Fig. 1 Substrate analogs prepared as inhibitors of saccharopine dehydrogenase.evaluated as inhibitors of the commercially available S. cerevisiae enzyme.79 Each analog was evaluated at an initial concentration of 2 mM in the presence of 1.7 mM saccharopine and 0.33 mM NAD+. Compound 10 in which the overall number of atoms and the disposition of the carboxy groups and nitrogens is the same as saccharopine showed significant inhibition of the enzyme. The a-aminopimelate analog 11 produced a very modest inhibition. Further characterization of 10 established a Ki of 0.12 mM. None of the compounds in Fig. 1 served as alternate substrates for saccharopine dehydrogenase. Thus the substrate specificity of the dehydrogenase for saccharopine in the forward direction appears to be nearly as strict as the a-ketoacid specificity in the reverse reaction.Also none of the derivatives in Fig. 1 were successful at affecting the growth of S. cerevisiae or C. albicans on solid medium. This may be in part due to poor uptake of these triacids into the cell. 3 Role of pipecolic acid in lysine metabolism l-Pipecolic acid is a common lysine metabolite found in various organisms including bacteria yeast plants and mammals.80,81 Numerous studies have demonstrated that l-pipecolic acid (l- PA) is primarily a product of lysine degradation although it can serve a nutritional role in some species of bacteria and yeast. Certain lysine auxotrophs of the aerobic red yeast Rhodotorula glutinis can grow on a minimal medium supplemented with l- PA.82,83 This yeast is able to use pipecolate as the sole nitrogen source but not as a carbon source.The studies showed that l-PA (16) serves as a precursor to lysine through oxidation to D1- piperideine-6-carboxylate (D1-P6C 17) and hydration to aaminoadipate-d-semialdehyde (7) which is converted to saccharopine (8) in the presence of glutamate and NADPH (Scheme 13).83 Following up on this finding Kinzel and Bhattacharjee reported the purification to near homogeneity and characterization of pipecolic acid oxidase from R. glutinis.84 The enzyme is a 43 kDa monomer exhibiting optimum activity at pH 8.5 with an apparent KM for l-PA of 1.67 mM. Molecular oxygen is required for activity and H2O2 is produced along with D1-P6C. Surprisingly the authors were unable to identify a flavin metal ion or any other redox cofactor to be associated with the enzyme.Pipecolic acid occurs as a minor intermediate of lysine metabolism in most mammalian tissues85–87 and a pipecolate oxidase has been purified from primate liver that shares many similarities with the yeast enzyme. The primate flavoenzyme is a membrane-associated 46 kDa monomer possessing a covalent Scheme 13 flavin with an apparent KM for pipecolic acid of 3.7 mM.88 Unlike the yeast enzyme which is reversibly inhibited by proline the primate oxidase can utilize l-proline as a poor alternate substrate. Evidence that pipecolic acid has neuromodulatory properties in the central nervous system (CNS) mediated through interactions with GABAA receptors has prompted the preparation of specific inhibitors of the primate enzyme.89–92 Differences between the yeast and primate enzymes are also observed in their ability to be inhibited by various pipecolate analogs and recognize others as alternate substrates.93 Furthermore the R.glutinis system is unique in that l-PA serves as a precursor to lysine rather than a lysine catabolite. The formation of pipecolic acid in fungi and yeast has been suggested to originate from both d- and l-lysine. Involvement of a lysine racemase was proposed by one group to account for this result94,95 while the intermediacy of l-pipecolate in the conversion of d-lysine to l-lysine was suggested by another.96 Fangmeier and Leistner sought to clarify the issue using d-[a- 15N]lysine and D-[e-15N]lysine in incorporation studies with N.crassa.97 When D-[e-15N]lysine (18) was administered to cultures of the fungus the label was detected in the a position of l-lysine (9) as well as in l-PA (16). However the l-PA and llysine isolated from cultures receiving d-[a-15N]lysine were not labeled with 15N. If an amino acid racemase was operating the isotopic label from 18 should be retained in the conversion to 9. When alanine and glutamate were isolated from the d-[a- 15N]lysine incorporation experiments they were enriched in 15N indicating a-ketoglutarate and pyruvate had served as nitrogen acceptors in transamination reactions. These observations support the pathway illustrated in Scheme 14 wherein a four step sequence converts d-lysine to l-lysine via the intermediacy of l-pipecolate.Scheme 14 The parasitic fungus Rhizoctonia leguminicola incorporates l-PA into the toxic octahydroindolizine alkaloids slaframine 93 Nat. Prod. Rep. 2000 17 85–97 and swainsonine the latter being a potent a-mannosidase inhibitor.98 Early studies on the biosynthesis of these alkaloids reported that pipecolate derived primarily from l-lysine via 6-amino-2-oxocaproic acid (19) and the imine D1-P2C (20).94 Because some pipecolate was found to originate from d-lysine the action of a lysine racemase was proposed. Reinvestigation of l-PA biosynthesis in R. leguminicola led to the unexpected finding that l-lysine was actually incorporated first into saccharopine (8) and then converted to 7.99 The enzyme converting 8 to 7 saccharopine oxidase is a 45 kDa monomeric flavoenzyme requiring O2 and producing the semialdehyde glutamate and H2O2.100 Semialdehyde 7 spontaneously cyclizes and dehydrates to form D1-P6C (17) which serves as substrate for an NADPH-requiring reductase yielding l-pipecolate (16) (Scheme 15).The l-PA produced by this route would possess a nitrogen originating from the a-amine of l-lysine and may explain findings that both d- and l-lysine can serve as precursors to 16. 4 Lysine catabolism Scheme 15 Role of saccharopine and pipecolic acid in R. leguminacola alkaloid biosynthesis. Lysine degradation is extremely varied in Nature and the nine known catabolic fates are depicted in Scheme 16. In mammals the major pathway of l-lysine degradation is through steps formally equivalent to the reversal of the fungal biosynthetic pathway.101–103 The first two steps of the process involve the sequential action of l-lysine-a-ketoglutarate reductase (Scheme 16; xii) and saccharopine dehydrogenase (glutamate forming) (Scheme 16; xiii).The net process is effectively a transamination with the e-amino group of l-lysine being transferred to a-ketoglutarate producing a-aminoadipate-dsemialdehyde and l-glutamate. In bovine and baboon liver and in human placenta both of these enzyme activities are associated with aminoadipic semialdehyde synthase a large (470–480 kDa) bifunctional tetramer composed of four identical subunits.104 In rat the activities are separable; the reductase purified from liver mitochondria is a tetramer with an apparent Scheme 16 Enzymes involved in the initial step of lysine degradation in various species i lysine 6-dehydrogenase EC 1.4.1.18; ii lysine:a-ketoglutarate e-aminotransferase EC 2.6.1.36; iii lysine:pyruvate 6-aminotransferase EC 2.6.1.71; iv lysine decarboxylase EC 4.1.1.18; v lysine oxidase EC 1.4.3.14; vi lysine dehydrogenase EC 1.4.1.15; vii lysine 2,3-aminomutase EC 5.4.3.2; viii lysine N6-hydroxylase EC 1.14.13.59 (lysine 6-monooxygenase (NADPH)); ix lysine N6-acetyltransferase EC 2.3.1.32; x lysine racemase EC 5.1.1.5; xi lysine 2-monooxygenase EC 1.13.12.2 (lysine oxygenase); xii saccharopine dehydrogenase (NADP+ L-lysine forming) EC 1.5.1.8 (lysine-a-ketoglutarate reductase); xiii saccharopine dehydrogenase (NAD+ L-glutamate forming) EC 1.5.1.9.Nat. Prod. Rep. 2000 17 85–97 94 MW 230 kDa and a subunit MW of 52 kDa while the dehydrogenase is a monomer of 43 kDa.105 Interestingly saccharopine is not produced in the CNS. In rat monkey and human brain l-lysine is specifically metabolized to l-pipecolate.86,87 In other tissues notably liver and kidney where the a-aminoadipate pathway is functional l-PA formation is a secondary process and D-lysine appears to be the precursor.86,106,107 Nitrogen-15 labeling studies showed that formation of l-pipecolate in mammals proceeds through the oxidative deamination of both d- and l-lysine to 6-amino- 2-oxocaproic acid.108 To date a lysine oxidase (Scheme 16; v) has not been characterized from brain. Similar to mammals plants degrade lysine primarily via saccharopine109 with some species also producing pipecolate.110,111 Bacteria alter l-lysine in the greatest number of ways.Clostridia and several other bacteria are able to process a-llysine to b-l-lysine through the action of lysine 2,3-aminomutase (Scheme 16; vii).112 The oxidative decarboxylation of lysine to 5-aminovaleramide has been observed in Pseudomonads possessing lysine 2-monooxygenase (Scheme 16; xi).113,114 Biosynthesis of the E. coli iron siderophore aerobactin begins with the formation of N6-hydroxylysine by a FAD-dependent monooxygenase (Scheme 16; viii). Some Pseudomonas species are able to decarboxylate lysine to yield cadaverine (Scheme 16; iv) and the decarboxylase has been purified from E.coli115 and Bacillus cadaveris.116 Lysine 6-dehydrogenase (Scheme 16; i) has been isolated from Agrobacterium tumefaciens and the product shown to be a-aminoadipate-d-semialdehyde.117 The same product is formed during lysine catabolism by several Pseudomonas species that possess lysine 6-aminotransferase activity (Scheme 16; ii).114 a-Aminoadipate-d-semialdehyde is the first intermediate in the utilization of lysine for b-lactam biosynthesis and lysine 6-aminotransferase has been identified in the b-lactam producers Streptomyces clavuligerus118 and Nocardia lactamdurans. 119 A survey of 28 yeast strains identified two lysine degradative pathways and separated the organisms into three groups depending on the first enzymatic step of the catabolism.120 Entry into the first pathway begins with formation of aaminoadipate-d-semialdehyde by either lysine 6-dehydrogenase (Scheme 16; i)121 or lysine 6-aminotransferase.Aminotransferases utilizing either pyruvate (Scheme 16; iii)122 or a-ketoglutarate (Scheme 16; ii)123 as amine acceptor have been found. Lysine 6-dehydrogenase activity was observed only in C. albicans and Kluyveromyces marxianus. Subsequent studies with the pathogen C. albicans revealed the enzyme accepts alternate substrates such as 4- and 5-hydroxylysine and thialysine.124 A second degradative route proceeds through acetylated intermediates. In some species the first step is catalyzed by lysine N6-acetyltransferase (Scheme 16; ix) followed by loss of the a-amine through transamination with aketoglutarate.125 The gene for a 391 residue lysine N6- acetyltransferase LYC1 from Y. lipolytica has been cloned and functionally expressed.126 Lysine racemase (Scheme 16; x) was suggested to function during the formation of pipecolic acid in R. leguminicola (Section 3).94 The activity was sensitive to hydroxylamine suggesting involvement of a pyridoxyl 5A-phosphate cofactor. This species also catabolizes lysine via acetylated intermediates. 95 The fungus Trichoderma viride produces a lysine a-oxidase that generates 6-amino-2-oxocaproic acid from l-lysine (Scheme 16; v).127 The enzyme is a FAD-containing homodimer comprised of two 56 kDa subunits and reportedly possesses in vitro and in vivo antitumor activity.DNA synthesis was more greatly affected than protein synthesis and the antiproliferative property was suggested to arise from the combined deprivation of lysine and formation of D1-P2C and H2O2.128 The red yeast R. glutinis can utilize lysine as the sole nitrogen source and lysine:a-ketoglutarate aminotransferase was shown to catalyze the transamination of the e-nitrogen of lysine to the a-position of glutamate with the concomitant formation of aaminoadipate-d-semialdehyde (Scheme 16; ii).123 Glutamate then serves as a more widely used nitrogen donor. Enzyme activity is markedly increased when cells were grown on lysine as the sole nitrogen source but is also detectable when cells received ammonia as their only source of nitrogen. This enzyme has been purified from C.utilis and characterized as a 83 kDa dimer possessing two identical 40 kDa subunits and requiring pyridoxal 5A-phosphate.129 Whereas a-ketoglutarate was the preferred amine acceptor oxaloacetate pyruvate and 2-oxoadipate can serve in this role. 5 Role of a-aminoadipate pathway intermediates in secondary metabolism There are numerous examples of fungal alkaloids or peptides that have lysine as a structural element or biosynthetic precursor and a survey of these falls outside the scope of this review. There are also cases where aminoadipate pathway intermediates are incorporated into secondary metabolites; one example is saccharopine serving as a precursor to slaframine and swainsonine cited above. Certainly the most well known and thoroughly studied case is the incorporation of a-aminoadipate into ACV the linear tripeptide precursor to the penicillins (Scheme 9 Section 2.5).The importance of a-aminoadipate availability on penicillin production is well documented. Adding a-aminoadipate to fermentations of P. chrysogenum can elevate the rate of ACV formation and levels of penicillin production.130,131 Furthermore lysine causes feedback inhibition of homocitrate synthase resulting in a reduced a-aminoadipate pool and a concomitant decrease in penicillin production.132 More recently Martin and co-workers demonstrated that disruption of the LYS2 gene encoding a-aminoadipate reductase in P. chrysogenum leads to penicillin overproduction.133 Both single and double crossover strategies were used to target the disruption of LYS2.The mutants lacked detectable a-aminoadipate reductase activity and produced penicillin levels more than double those of the parent strain. The increased production likely results from diminished feedback inhibition by lysine and an increased flux of aminoadipate towards penicillin production. 134 Martin’s group also presented evidence that it is lysine catabolism in P. chrysogenum that yields the a-aminoadipate entering the penicillin biosynthetic pathway.135 They identified a P. chrysogenum lysine auxotroph unable to form aaminoadipate but which could still produce penicillin when supplemented with lysine.136 Further studies with this mutant indicated that [U-14C]lysine was incorporated into saccharopine and a-aminoadipic acid providing evidence that the catabolism proceeded by a reversal of the sequential actions of saccharopine dehydrogenase and saccharopine reductase.The aaminoadipate pool for penicillin production in P. chrysogenum is sequestered from the cytosol.137 Vacuoles were later identified as the sequestration site and shown to contain cysteine and valine as well as having ACV synthetase loosely associated with the vacuolar membrane.55 Hence the substrates and enzyme for the assembly of the first committed precursor to penicillin are compartmentalized although the enzyme using ACV as substrate isopenicillin N synthetase is cytosolic.55 Interestingly lysine 6-aminotransferase the enzyme that converts lysine directly to a-aminoadipate-d-semialdehyde was also detected in the P.chrysogenum mutant and a NAD+- dependent oxidation of a-aminoadipate-d-semialdehyde to aaminoadipate was observed. This particular catabolic route is well known in actinomycetes that produce penicillins.138 The gene for lysine 6-aminotransferase is associated with the cephamycin biosynthetic gene cluster in N. lactamdurans119 95 Nat. Prod. Rep. 2000 17 85–97 and the gene encoding piperideine-6-carboxylate dehydrogenase the enzyme oxidizing the semialdehyde to a-aminoadipate is found with the cephamycin gene cluster in S. clavuligerus.139 6 The a-aminoadipate pathway in archaea and bacteria The first evidence that the a-aminoadipate pathway may operate in certain bacteria was encountered in acetate incorporation studies with the thermophilic anaerobic archaeon Thermoproteus neutrophilus.140 Labeling patterns seen in lysine were consistent with a biosynthesis proceeding through the intermediacy of aminoadipate rather than diaminopimelate.This represented the first evidence for operation of the pathway outside of higher fungi and Euglenoids. In the bacterial biosynthesis of lysine threonine and methionine the first step is catalyzed by aspartate kinase and this enzyme is sensitive to feedback inhibition by each of these amino acids. Observations that aspartate kinase from the aerobic Gram-negative thermophile Thermus flavus was inhibited by threonine and methionine but not by lysine suggested that this organism may not use the diaminopimelate pathway.141 Kosuge and Hoshino analyzed the predicted amino acid sequences of two ORFs residing on a 3.8 kb fragment of DNA from the bacterium Thermus thermophilus and found 55% and 45% identity with S.cerevisiae homocitrate synthase and homoaconitase respectively.142 Gene disruption experiments resulted in lysine auxotrophy which could be complemented by aminoadipate but not by diaminopimelate. Similarly Kobashi et al. generated lysine auxotrophs of T. thermophilus and found none could survive on minimal medium supplemented with diaminopimelate but growth was seen when aminoadipate was added.143 A 4.3 kb DNA fragment was cloned that complemented the lysine auxotrophy and sequence analysis identified two genes HACA and HACB that were proposed to encode subunits of homoaconitate hydratase.Mutants with a disrupted HACA gene could not grow on minimal medium unless lysine was added but growth was observed if the disruptants received supplemental a-aminoadipate or a-ketoglutarate. Homocitrate synthase activity was observed in the wild-type T. thermophilus. 7 Conclusion Systemic fungal infections are among the most difficult infectious diseases to treat. The uniqueness of the aminoadipate pathway has prompted speculation that these enzymes may be viable targets for selective antifungal agents. Similarly the novelty of several genes in the pathway may permit them to serve as molecular markers to facilitate rapid identification of fungal pathogens. Bhattacharjee has already demonstrated the feasibility of using PCR to amplify conserved regions in lysine biosynthetic genes to identify C.albicans.53,144 Inasmuch as plants utilize the diaminopimelate pathway to lysine targeting fungal lysine biosynthesis may prove to be an effective fungicidal tactic. Our understanding of the a-aminoadipate pathway to lysine at the molecular level has increased dramatically in recent years paralleling the growth in genomic information. This trend is likely to continue and one can anticipate resolution of the unanswered biochemical questions in the pathway and additional insight into the evolution of the multiple routes for lysine formation and degradation in diverse organisms. 8 Acknowledgements Prof. Christopher Walsh is gratefully acknowledged for providing a preprint of a paper describing the role of Lys 5.Dr Philip Proteau is thanked for critically reading the manuscript. Research in the author’s laboratory on lysine metabolism has Nat. Prod. Rep. 2000 17 85–97 96 been supported in part by NIH grant NS 32421 and the Medical Research Foundation of Oregon. 9 References 1 R. J. Cox Nat. Prod. Rep. 1996 13 29. 2 G. Scapin and J. S. Blanchard Adv. Enzymol. Relat. Areas Mol. Biol. 1998 72 279. 3 R. Ledwidge and J. S. Blanchard Biochemistry 1999 38 3019. 4 J. K. Bhattacharjee Crit. Rev. Microbiol. 1985 12 131. 5 J. K. Bhattacharjee in Evolution of a-Aminoadipate Pathway for the Synthesis of Lysine in Fungi ed. R. P. Mortlock CRC Press Boca 6 M.Strassman and L. N. Ceci Biochem. Biophys. Res. Commun. 1964 7 A. F. Tucci and L. N. Ceci Arch. Biochem. Biophys. 1972 153 8 A. F. Tucci and L. N. Ceci Arch. Biochem. Biophys. 1972 153 9 J. W. Tracy and G. B. Kohlhaw Proc. Natl. Acad. Sci. U.S.A. 1975 Raton FL 1992 pp. 47. 14 262. 742. 751. 72 1802. 10 W. M. Jaklitsch and C. P. Kubicek Biochem. J. 1990 269 247. 11 P. Verhasselt M. Voet and G. Volckaert Yeast 1995 11 961. 12 F. Ramos P. Verhasselt A. Feller P. Peeters A. Wach E. Dubois and G. Volckaert Yeast 1996 12 1315. 13 S. Chen S. Brockenbrough J. E. Dove and J. P. Aris J. Biol. Chem. 1997 272 10839. 14 F. M. Perez-Campo J. M. Nicaud C. Gaillardin and A. Dominguez Yeast 1996 12 1459. 15 O. Banuelos J. Casqueiro F. Fierro M.J. Hijarrubia S. Gutierrez and J. F. Martin Gene 1999 226 51. 16 J. K. Bhattacharjee A. F. Tucci and M. Strassman Arch. Biochem. Biophys. 1968 123 235. 17 M. Strassman and L. N. Ceci J. Biol. Chem. 1966 241 5401. 18 H. Betterton T. Fjellstedt M. Matsuda M. Ogur and R. Tate Biochim. Biophys. Acta 1968 170 459. 19 L. Wang S. Okamoto and J. K. Bhattacharjee Curr. Genet. 1989 16 7. 20 G. Weidner B. Steffan and A. A. Brakhage Mol. Gen. Genet. 1997 255 237. 21 F. Gamonet and G. J. Lauquin Eur. J. Biochem. 1998 251 716. 22 S. D. Irvin and J. K. Bhattacharjee J. Mol. Evol. 1998 46 401. 23 J. Horecka P. T. Kinsey and G. F. J. Sprague Gene 1995 162 87. 24 V. C. Culotta L. W. Klomp J. Strain R. L. Casareno B. Krems and J. D. Gitlin J. Biol. Chem. 1997 272 23469.25 M. Strassman and L. N. Ceci J. Biol. Chem. 1965 240 4357. 26 C. M. Gaillardin A. M. Ribet and H. Heslot Eur. J. Biochem. 1982 128 489. 27 Z. H. Ye R. C. Garrad M. K. Winston and J. K. Bhattacharjee J. Basic Microbiol. 1991 31 149. 28 L. A. Urrestarazu C. W. Borell and J. K. Bhattacharjee Curr. Genet. 1985 9 341. 29 M. K. Winston and J. K. Bhattacharjee Curr. Genet. 1987 11 393. 30 H. P. Broquist A. V. Stiffey and A. M. Albrecht J. Biol. Chem. 1961 9 1. 31 N. Piediscalzi T. Fjellstedt and M. Ogur Biochem. Biophys. Res. Commun. 1968 32 380. 32 M. Matsuda and M. Ogur J. Biol. Chem. 1969 244 3352. 33 M. Matsuda and M. Ogur J. Biol. Chem. 1969 244 5153. 34 Y. Asada Y. Sawa and K. Tanizawa J. Biochem. 1986 99 1101. 35 M. R.Mawal and D. R. Deshmukh J. Biol. Chem. 1991 266 2573. 36 R. Buchli D. Alberati-Giani P. Malherbe C. Kohler C. Broger and A. M. Cesura J. Biol. Chem. 1995 270 29330. 37 A. Urrestarazu S. Vissers I. Iraqui and M. Grenson Mol. Gen. Genet. 1998 257 230. 38 A. K. Sinha and J. K. Bhattacharjee Biochem. Biophys. Res. Commun. 1970 39 1205. 39 D. R. Storts and J. K. Bhattacharjee Biochem. Biophys. Res. Commun. 1989 161 182. 40 A. K. Sinha and J. K. Bhattacharjee Biochem. J. 1971 125 743. 41 K. S. Zaret and F. Sherman J. Bacteriol. 1985 162 579. 42 H. Eibel and P. Philippsen Mol. Gen. Genet. 1983 191 66. 43 D. A. Barnes and J. Thorner Mol. Cell. Biol. 1986 6 2828. 44 U. N. Fleig R. D. Pridmore and P. Philippsen Gene 1986 46 237. 45 M. E. Morris and S.Jinks-Robertson Gene 1991 98 141. 46 R. Weckermann R. Furbass and M. A. Marahiel Nucleic Acids Res. 1988 16 11841. 47 A. Pospiech J. Bietenhader and T. Schupp Microbiology 1996 142 741. 48 C. W. Borell and J. K. Bhattacharjee Curr. Genet. 1988 13 299. 49 S. Rajnarayan J. C. Vaughn and J. K. Bhattacharjee Curr. Genet. 1992 21 13. 50 K. G. Miller and J. K. Bhattacharjee Gene 1996 172 167. 51 R. A. Ford and J. K. Bhattacharjee Curr. Genet. 1995 28 131. 52 V. Bhattacherjee and J. K. Bhattacharjee Yeast 1998 14 479. 53 K. Suvarna L. Seah V. Bhattacherjee and J. K. Bhattacharjee Curr. Genet. 1998 33 268. 54 J. Casqueiro S. Gutierrez O. Banuelos F. Fierro J. Velasco and J. F. Martin Mol. Gen. Genet. 1998 259 549. 55 T. Lendenfeld D. Ghali M. Wolschek E.M. Kubicek-Pranz and C. P. Kubicek J. Biol. Chem. 1993 268 665. 56 H. Schmidt R. Bode M. Lindner and D. Birnbaum J. Basic Microbiol. 1985 25 675. 57 G. Kunze R. Bode H. Schmidt I. A. Samsonova and D. Birnbaum Curr. Genet. 1987 11 385. 58 R. H. Lambalot A. M. Gehring R. S. Flugel P. Zuber M. LaCelle M. A. Maraheil R. Reid C. Khosla and C. T. Walsh Chem. Biol. 1996 3 923. 59 D. E. Ehmann A. M. Gehring and C. T. Walsh Biochemistry 1999 38 6171. 60 D. R. Storts and J. K. Bhattacharjee J. Bacteriol. 1987 169 416. 61 C. W. Borell L. A. Urrestarazu and J. K. Bhattacharjee J. Bacteriol. 1984 159 429. 62 F. Ramos E. Dubois and A. Pierard Eur. J. Biochem. 1988 171 171. 63 H. Ogawa and M. Fujioka J. Biol. Chem. 1978 253 3666. 64 M. Fujioka Arch.Biochem. Biophys. 1984 230 553 and references cited therein. 65 M. Fujioka and Y. Nakatani Eur. J. Biochem. 1970 16 180. 66 M. Fujioka and Y. Takata Biochim. Biophys. Acta 1979 570 210. 67 M. Fujioka and M. Tanaka Eur. J. Biochem. 1978 90 297. 68 M. Fujioka Y. Takata H. Ogawa and M. Okamoto J. Biol. Chem. 1980 255 937. 69 H. Ogawa and M. Fujioka J. Biol. Chem. 1980 255 7420. 70 M. Fujioka and Y. Takata Biochemistry 1981 20 468. 71 H. Ogawa M. Okamoto and M. Fujioka J. Biol. Chem. 1979 254 7030. 72 H. Ogawa T. Hase and M. Fujioka Biochim. Biophys. Acta 1980 623 225. 73 J. W. Xuan P. Fournier and C. Gaillardin Curr. Genet. 1988 14 15. 74 J. S. Trupin and H. P. Broquist J. Biol. Chem. 1965 240 2524. 75 Z. H. Ye and J. K. Bhattacharjee J.Bacteriol. 1988 170 5968. 76 R. C. Garrad and J. K. Bhattacharjee J. Bacteriol. 1992 174 7379. 77 R. Garrad T. M. Schmidt and J. K. Bhattacharjee Infect. Immun. 1994 62 5027. 78 M. G. Shepard Infect. Immun. 1985 50 541. 79 B. Ho and T. M. Zabriskie unpublished results. 80 V. W. Rodwell Methods. Enzymol. 1971 17B 174. 81 H. P. Broquist Annu. Rev. Nutr. 1991 11 435. 82 M. Kurtz and J. K. Bhattacharjee J. Gen. Microbiol. 1975. 83 J. J. Kinzel and J. K. Bhattacharjee J. Bacteriol. 1979 138 410. 84 J. J. Kinzel and J. K. Bhattacharjee J. Bacteriol. 1982 151 1073. 85 S. J. Mihalik and W. J. Rhead J. Comp. Physiol. B 1991 160 671. 86 Y. F. Chang Neurochem. Res. 1982 7 577. 87 Y. F. Chang J. Neurochem. 1978 30 347. 88 S. J. Mihalik M. McGuinness and P.A. Watkins J. Biol. Chem. 1991 266 4822. 89 B. Ho and T. M. Zabriskie Bioorg. Med. Chem. Lett. 1998 8 739. 90 T. M. Zabriskie J. Med. Chem. 1996 39 3046. 91 T. M. Zabriskie and X. Liang Bioorg. Med. Chem. Lett. 1997 7 457. 92 T. M. Zabriskie W. L. Kelly and X. Liang J. Am. Chem. Soc. 1997 119 6446. 93 T. M. Zabriskie unpublished data. 94 F. P. Guengerich and H. P. Broquist Biochemistry 1973 12 4270. 95 F. P. Guengerich and H. P. Broquist J. Bacteriol. 1976 126 338. 96 W.-U. Müller and E. Leistner Z. Naturforsch. 1975 30c 253. 97 N. Fangmeier and E. Leistner J. Biol. Chem. 1980 255 10205. 98 H. P. Broquist P. S. Mason B. Wickwire R. Homann M. J. Schneider and T. M. Harris in Swainsonine Production in the Mold Rhizoctonia leguminicola ed.A. A. Seawright M. P. Hegarty L. F. James and R. F. Keeler Yeerongpilly Australia 1985 pp. 301. 99 B. M. Wickwire C. M. Harris T. M. Harris and H. P. Broquist J. Biol. Chem. 1990 265 14742. 100 B. M. Wickwire C. Wagner and H. P. Broquist J. Biol. Chem. 1990 265 14748. 101 K. Higashino K. Tsukada and I. Lieberman Biochem. Biophys. Res. Commun. 1965 20 285. 102 J. Hutzler and J. Dancis Biochim. Biophys. Acta 1968 158 62. 103 J. Hutzler and J. Dancis Biochim. Biophys. Acta 1975 377 42. 104 P. J. Markovitz D. T. Chuang and R. P. Cox J. Biol. Chem. 1984 259 11643. 105 C. Noda and A. Ichihara Biochim. Biophys. Acta 1978 525 307. 106 J. Dancis and J. Hutzler Biochim. Biophys. Acta 1981 675 411. 107 J. Dancis and J. Hutzler Comp. Biochem.Physiol. 1982 73B 1011. 108 J. A. Grove T. J. Gilbertson R. H. Hammerstedt and L. M. Henderson Biochim. Biophys. Acta 1969 184 329. 109 G. Tang D. Miron J. X. Zhu-Shimoni and G. Galili Plant Cell 1997 9 1305. 110 H. R. Schuette and G. Seelig Z. Naturforsch. 1967 22b 824. 111 A. Cincerova and E. Cerna Z. Pflanzenphysiol. 1974 74 366. 112 T. P. Chirpich V. Zappia R. N. Costilow and H. A. Barker J. Biol. Chem. 1970 245 1778. 113 H. Takeda S. Yamamoto Y. Kojima and O. Hayaishi J. Biol. Chem. 1969 244 2935. 114 J. C. Fothergill and J. R. Guest J. Gen. Microbiol. 1977 99 139. 115 E. A. Boeker and E. H. Fisher Methods Enzymol. 1983 94 180. 116 K. Soda and M. Moriguchi Biochem. Biophys. Res. Commun. 1969 34 34. 117 H. Misono H. Uehigashi E.Morimoto and S. Nagasaki Agric. Biol. Chem. 1985 49 2253. 118 J. Romero J. F. Martin P. Liras A. L. Demain and N. Rius J. Ind. Microbiol. Biotechnol. 1997 18 241. 119 J. J. Coque P. Liras L. Laiz and J. F. Martin J. Bacteriol. 1991 173 6258. 120 T. Hammer R. Bode H. Schmidt and D. Birnbaum J. Basic Microbiol. 1991 31 43. 121 T. Hammer R. Bode and D. Birnbaum J. Gen. Microbiol. 1991 137 711. 122 H. Schmidt R. Bode and D. Birnbaum FEMS Microbiol. Lett. 1988 49 203. 123 J. J. Kinzel M. K. Winston and J. K. Bhattacharjee J. Bacteriol. 1983 155 417. 124 T. Hammer and R. Bode Zentralbl. Mikrobiol. 1992 147 65. 125 P. J. Large and A. Robertson FEMS Microbiol. Lett. 1991 66 209. 126 J. M. Beckerich M. Lambert and C. Gaillardin Curr. Genet. 1994 25 24. 127 H. Kusakabe K. Kodama A. Kuninaka H. Yoshino H. Misono and K. Soda J. Biol. Chem. 1980 255 976. 128 H. Kusakabe K. Kodama A. Kuninaka H. Yoshino and K. Soda Agric. Biol. Chem. 1980 44 387. 129 T. Hammer and R. Bode J. Basic Microbiol. 1992 32 21. 130 G. C. Friedrich and A. L. Demain Arch. Microbiol. 1978 119 43. 131 W. M. Jaklitsch W. Hampel M. Rohr C. P. Kubicek and G. Gamerith Can. J. Microbiol. 1986 32 473. 132 A. A. Brakhage and G. G. Turner FEMS Microbiol. 1992 12 123. 133 J. Casqueiro S. Gutierrez O. Banuelos M. J. Hijarrubia and J. F. Martin J. Bacteriol. 1999 181 1181. 134 Y. Lu R. L. Mach K. Affenzeller and C. P. Kubicek Can. J. Microbiol. 1992 38 758. 135 C. Esmahan E. Alvarez E. Montenegro and J. F. Martin Appl. Environ. Microbiol. 1994 60 1705. 136 J. M. Luengo J. R. Revilla M. J. López J. R. Villanueva and J. F. Martin J. Bacteriol. 1980 144 869. 137 C. Hönlinger and C. P. Kubicek Biochim. Biophys. Acta 1989 993 204. 138 K. Madduri C. Stuttard and L. C. Vining J. Bacteriol. 1989 171 299. 139 F.J. Pérez-Llarena A. Rodriguez-Garcia F. J. Enguita J. F. Martin and P. Liras J. Bacteriol. 1998 180 4753. 140 S. Schafer T. Paalme R. Vilu and G. Fuchs Eur. J. Biochem. 1989 186 695. 141 M. Nishiyama M. Kukimoto T. Beppu and S. Horinouchi Microbiology 1995 141 1211. 142 T. Kosuge and T. Hoshino FEMS Microbiol. Lett. 1998 169 361. 143 N. Kobashi M. Nishiyama and M. Tanokura J. Bacteriol. 1999 181 1713. 144 V. Bhattacherjee and J. K. Bhattacharjee 96th Annu. Meet. Am. Soc. Microbiol. 1996 Abstr F. Review a801345d 97 Nat. Prod. Rep. 2000 17 85–97

ISSN:0265-0568    

DOI:10.1039/a801345d

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Iron chelators from mycobacteria (1954–1999) and potential therapeutic applications Anne F. Vergne Andrew J. Walz and Marvin J. Miller* Department of Chemistry & Biochemistry University of Notre Dame 251 Nieuwland Science Hall Notre Dame IN46556-5670 USA 7 Received (in Cambridge UK) 11th August 1999 Covering 1954 to 1999 Previous review 1970 4 Isolation and characterization of exochelins and carboxymycobactins 8 Biosynthesis of mycobactins and exochelins 8.1 Isotopic labeling studies of mycobactin biosynthesis 8.2 Identification of gene clusters encoding for biosyntheses of mycobactin T and exochelins of Introduction Discovery of mycobactins Production extraction and purification of 123 mycobactins 3.1 Production 3.2 Extraction and purification 45 Structure elucidation of mycobactins M.smegmatis 9 Iron transport mechanisms in mycobacteria 9.1 Introduction 9.2 Mycobactin in the cell envelope 9.3 Iron sequestration and transport utilizing salicylate 9.4 Iron sequestration and transport utilizing citrate 9.5 Iron sequestration and transport utilizing exochelins 9.6 Iron sequestration and transport utilizing Possible therapeutic applications of mycobacterial carboxymycobactins 9.7 Iron regulated envelope proteins as possible receptors for extracellular ferrisiderophores 9.8 Iron release and storage in mycobacteria 10 and mycobacterial-like siderophores targeting the iron uptake mechanisms of mycobacteria 10.1 Introduction Physical and chemical properties of mycobactins 5.1 Ultraviolet absorption spectrum 5.2 Mass spectrometry 5.3 Chromatographic properties 5.4 NMR 6 Synthesis of mycobactins and mycobactin analogs 6.1 Synthesis of oxazoline derivative 4 6.2 Synthesis of hydroxamic acid units 5 and 7 6.3 Synthesis of mycobactic acid 2 6.4 Synthesis of cobactin 3 and analogs 6.5 Synthesis of mycobactin 1 and analogs Anne Vergne was born in France in 1975.She completed her undergraduate studies at CPE-Lyon France (School of Chemistry-Physics-Electronics). In 1997 she joined the research group of Professor Marvin J. Miller at the University of Notre- Dame IN. She is currently a third-year graduate student and her research interests focus on the synthesis of mycobactin analogues with potential antituberculosis and antitumor activities.Marvin Miller was born and raised in Dickinson ND. His interest in organic chemistry was inspired by the enthusiasm of Professor S. P. Pappas his undergraduate mentor at North Dakota State. Professor Marc Loudon introduced him to hydroxamic acid chemistry during Ph.D. studies at Cornell. Subsequent to an NIH postdoctoral fellowship with Professor Henry Rapoport at Berkeley Dr. Miller joined the faculty of Notre Dame in 1977 where he is now the George and Winifred Clark Professor of Chemistry. Current research interests include synthesis and studies of biologically important molecules. He is sustained by the love of his wife Patty and children Chris Katie Joe and Carl. Marvin Miller Andrew Walz received his B.S.degree in 1994 from Kent State University. His undergraduate research conducted under the direction of Dr. L.-C. Chien of the Liquid Crystal Institute dealt with the synthesis of polysiloxane based liquid crystals. He received his Ph.D. from the University of Virginia in 1999 under the direction of Dr. Richard J. Sundberg. His graduate research focussed on the synthesis of heterocyclic marine natural products and analogs as potential protein kinase C inhibitors. He is presently a postdoctoral research associate with Dr. Marvin J. Miller working on the synthesis of mycobactin analogs. He enjoys the loving support of his wife Elizabeth and two sons Jack and Frank. Anne Vergne Andrew Walz 99 Nat. Prod.Rep. 2000 17 99–116 This journal is © The Royal Society of Chemistry 2000 10.2 Mycobactins and mycobactin analogs as anti-mycobacterial agents Snow’s hypothesis 10.3 Other strategies targeting the iron uptake mechanisms of mycobacteria for possible therapeutic applications 10.4 Siderophore-mediated drug transport as a means for treating mycobacterial infections Other possible therapeutic applications of 11 mycobacterial siderophores Conclusion Acknowledgments References 12 13 14 1 Introduction Iron is an essential nutrient for virtually all forms of life. Indeed iron is utilized in oxygen transport electron transport and other fundamental and life sustaining biological functions. Thus the acquisition of iron by an organism is necessary for survival.Siderophores Greek for ‘iron carriers’ are low-molecular weight iron chelating compounds generated by plants microbes and even higher organisms for the acquisition of iron.1–3 Mycobacteria synthesize and utilize at least three types of siderophores the mycobactins exochelins and carboxymycobactins. Mycobactins were the first mycobacterial siderophores discovered and extensively studied. An excellent comprehensive review of these compounds was written by G. A. Snow in 1970.4 Since that time no comprehensive review has appeared in the literature covering all three known types of mycobacterial siderophores. Other reviews have been written concerning mycobacterial iron transport and metabolism involving these siderophores.5–7 This review will examine the past and current literature concerning the discovery isolation structure elucidation chemical properties synthesis biological function and therapeutic potential of these iron chelating natural products while highlighting important material covered in the existing reviews.Although this area of research is interesting as basic science the recent rise in mycobacterial infections worldwide most notably those due to Mycobacterium tuberculosis and M. avium adds significance to this review as will be discussed in the text. Table 1 General structure of mycobactins Nat. Prod. Rep. 2000 17 99–116 100 2 Discovery of mycobactins In the 1910’s M. paratuberculosis then called M. johnei was a microorganism of considerable interest and research because it had been determined to be the cause of cattle disease that resulted in considerable losses to farmers of Europe.However M. paratuberculosis and a bacillus found in the lesions of leprosy were the only two mycobacteria that could not be grown on laboratory media. In 1912 Twort and Ingram managed to grow M. paratuberculosis by adding killed human tubercle bacilli to the synthetic medium.8 So they suggested the existence of an essential growth factor from other mycobacteria that M. paratuberculosis was unable to produce itself. Subsequently extracts of M. phlei were added to synthetic media in order to promote growth of M. paratuberculosis but no attempt was made to isolate the unknown growth factor(s) until 1949 when Francis Macturk Madinaveitia and Snow isolated it from M.phlei.9 They managed to crystallize the growth factor as an aluminum complex but failed to isolate it in a metal-free form. A few years later in 1953 the same authors isolated from M. phlei the growth factor for M. paratuberculosis for which they suggested the name mycobactin.10 They described a new extraction method that allowed them to obtain pure mycobactin in a metal-free form. In 1954 the first structure of a mycobactin was determined by chemical degradation of mycobactin P and identification of its constituent fragments.11 Mycobactin P actually is a mixture of four similar chemical entities differing only in a fatty side chain. Two possible core structures were proposed,12 and it was only in 1965 that Snow13 determined the correct structure (See Table 1) established the absolute configuration of all of the stereocenters and obtained the active ferric complex of mycobactin P in crystalline form.In the same year the growth factor from M. tuberculosis was discovered by Marks.14,15 It was called mycobactin T in order to distinguish it from mycobactin P the growth factor from M. phlei.16 Mycobactin T was isolated by Snow from M. tuberculosis as an iron complex in 1965.17 As with mycobactin P it also was a mixture of at least four different components differing only in their fatty acid side chains; the structure of the main component was determined and appeared to be very similar to the structure of mycobactin P. In 1968 Snow and White utilized thin-layer chromatography of the ferric or aluminum complexes to separate and identify the different mycobactins isolated from different mycobacteria.18 They were able to determine that M.terrae M. marinum and M. smegmatis produce mycobactins that differ from each other and from mycobactins P and T. In order to distinguish the mycobactins a nomenclature was also suggested. Mycobactins possessing the same nucleus and forming a homologous series with various side-chain lengths form a family designated by a letter. Indication of the number of carbons in the side chain is used to differentiate the different members of a family. From these early studies it appeared that most species of mycobacteria grown in iron-deficient media produce mycobactins and that different strains of mycobacteria produce mycobactins with differing substructures.Subsequently mycobactins from several different strains of mycobacteria have been isolated and structurally compared to those previously characterized. 19 All the known structures of mycobactins are summarized in Table 1.19–22 M. paratuberculosis and other strains of pathogenic mycobacteria upon initial laboratory isolation require the addition of an external mycobactin growth factor for cultivation as mentioned previously. This ‘mycobactin dependence’ can be lost in subsequent generations following the initial cultivation resulting in mycobactin production by the isolants under appropriate conditions. This led to a controversy related to the discovery of the mycobactin produced by M.paratuberculosis23 since two different structures were proposed mycobactin J and mycobactin ‘J’.20,24,25 This controversy was resolved in 1992 by Barclay Furst and Smith26 who found that mutants of M. paratuberculosis were selected during growth under iron-deficient conditions suggesting that two different mycobactins could have been isolated by the two groups. 3 Production extraction and purification of mycobactins Isolation of mycobactins requires growth of mycobacteria followed by extraction and purification of the mycobactins. Various methods used for these three steps are only briefly summarized and updated in this section since complete early details were provided by Snow.4 3.1 Production After the first isolation of a mycobactin in 1953,10 satisfactory liquid media were developed for the growth of mycobacteria and improved18 by White and Snow based on the early observation that the microorganisms had to be grown under iron-deficient conditions.4 These media contained KH2PO4 Na2HPO4 glycerol and asparagine in water.18 In a few cases of mycobactin-dependent mycobacteria such as certain strains of M.paratuberculosis M. avium and M. leprae it was necessary to add some mycobactins to the growth medium. In order to insure iron deficiency the glassware had to be carefully treated with acid. In 1982 Hall and Ratledge proposed a convenient method for the production of mycobactins which did not require acid cleaning of the glassware.27 The usual glycerol– asparagine–salt medium was solidified using agar leading to a much more convenient procedure.With both the stirred liquid or solid synthetic media growth of the microorganisms was slow. However in 1993 a new method was developed to produce mycobactins in high iron concentration conditions in the presence of ethylenediaminodi(o-hydroxyphenylacetic acid) (EDDA) an iron chelator.28 The authors described a twostep method where the mycobacteria were initially grown in an iron-containing medium and then shifted to an EDDAcontaining medium for the mycobactin production phase. 3.2 Extraction and purification Francis Snow and co-workers developed the first method to extract and purify a mycobactin in a metal-free form10 but in 1965 the attempted isolation of mycobactin T with the same method failed because it was entirely present as the ironcomplex.17 In 1969 White and Snow described general methods applicable to most of the mycobactins that allowed obtention of either ferric mycobactins or mycobactins in a metal-free form.4,22 These methods are still the basis of procedures used today.24,29 Eventually simplified purification methods of the mycobactins were reported by Ratledge and Hall in 198227,30 and 1986.31 These consist in scraping the cells from the solid medium extracting with ethanol and after treatment with FeCl3 further extraction with chloroform and methanol. It should be re-emphasized that the criterion of purity of mycobactins is not the presence of a single chemical compound since all but mycobactins A and R are isolated as mixtures of homologues differing only in the length of the fatty acid side chain.The criterion of purity refers then to the absence of mycobactins with a different nucleus or any other organic molecule. Except for M. marinum which produces separable mycobactins M and N and M. fortuitum which produces inseparable mycobactins F and H mycobacteria produce only one major type of mycobactin. Traces of other types are removed by purification. Separation of homologous components has been effected for the major component of mycobactin P by counter-current distribution18 and more recently HPLC separation of homologous components of mycobactin S has been accomplished (See Section 5.3).4 Structure elucidation of mycobactins The first structure elucidation of a mycobactin was determined by Snow in 1954 through chemical degradation of mycobactin P (Scheme 1).11 Treatment of mycobactin P under mildly basic conditions cleaved the ester linkage affording two compounds mycobactic acid P and cobactin P. Subsequent acid hydrolysis of mycobactic acid P yielded (a) 6-methylsalicylic acid which underwent degradation to afford m-cresol and carbon dioxide; (b) a b-hydroxy amino acid (serine); (c) Ne-hydroxy-L-lysine and (d) a mixture of long chain fatty acids in most cases a,b unsaturated. Acid hydrolysis of cobactin P afforded two fragments (e) a b-hydroxy acid and (f) another Ne-hydroxy-llysine. From this chemical degradation two structures were possible.12 In 1965 Snow determined by oxidation of mycobactic acid P with periodate that the side-chain was attached by a hydroxamic acid linkage rather than an amide linkage.13 The stereochemistry of all asymmetric centers was also determined by comparison of the optical rotations UV and IR spectra and GC retention times of the degradation products with reference compounds.The same methods of chemical degradation were applied to determine the structures of mycobactin T17 and mycobactins S and H.22 A method to determine the structure of mycobactins by NMR,32 developed by Greatbanks and Bedford complemented the existing chemical degradation methods. Similarly in 1982 in order to elucidate the structure of mycobactin J,25 McCullough and Merkal used mass spectroscopy and NMR (proton and carbon) of both the intact molecule and its fragment cobactin J1.By comparing their results with the known data for mycobactin P the authors determined the structure of mycobactin J. Fragments (c) and (f) were as for the other mycobactins forms of Ne-hydroxy-l-lysine. The b-hydroxy fragment (e) 2,4-dimethyl-3-hydroxypentanoic acid differed from previously known cobactins because it contained an isopropyl group. In summary two types of mycobactins can be distinguished mycobactins P T A R F H S and J have the same core structure but differ only in details of substitution and absolute stereochemistry. However mycobactins M and N from M. marinum differ from the others by having only small acyl groups at the hydroxamic group of the mycobactic acid moiety.101 Nat. Prod. Rep. 2000 17 99–116 Scheme 1 Chemical degradation of mycobactin P (Reproduced by permission from G. A. Snow Bacteriol. Rev. 1970 34 99). In 1974 Hough and Rogers determined the X-ray structure of ferrimycobactin P which delineated the coordination of iron by mycobactins.33 Ferrimycobactin can be considered as a sphere of diameter between 11 and 14 Å. Six atoms five oxygens and one nitrogen coordinate the Fe(iii) atom and form a particularly strained octahedron. The metal atom lies in a ‘V-shaped cleft’. According to the authors the dimensions of the octahedron can explain both the ‘high stability of the iron-complex of mycobactins and the ease of release of the iron atom’.Studies on the scandium yttrium and lanthanum complexes of mycobactin S showed that these IIIb cations form 1+1 complexes with mycobactin S. Semi-empirical calculations predict nonoctahedral configuration of the siderophore about these metal cations contrary to the iron(iii) complexes.34 5 Physical and chemical properties of mycobactins This section will give a brief overview of the physical and chemical properties of mycobactins reviewed in detail by Snow4 and will present the results reported since then. When isolated pure in a metal-free form all known mycobactins are white powders whose melting points are definite occurring between 155 °C and 175 °C.10,17,21,22 Mycobactins have very poor solubility in water (5 to 15 mg mL21 at 20 °C).Their solubility in non-polar solvents such as ether benzene or aliphatic hydrocarbons is low but they are somewhat soluble in ethanol (2% at 20 °C) and even more soluble in chloroform. 5.1 Ultraviolet absorption spectra The main structural features accounting for the UV-adsorption of mycobactins are the hydroxyphenyl-oxazoline residue and the acyl-hydroxamic acid groups. Two general types of spectra are obtained one with lmax in methanol at 243 249 and 304 nm if the benzyl group is substituted and lmax at 250 and 311 nm if not.4 Nat. Prod. Rep. 2000 17 99–116 102 5.2 Mass spectrometry Mass spectra of aluminum complexes of mycobactins can be easily obtained and are very useful for identification of mycobactins.4,21 First the parent peaks allow a determination of the molecular weight.As indicated earlier mycobactins are in most cases mixtures of homologues differing only in their side chain. Since the components have similar volatility the relative abundance can be measured. Eventually the first degradation peak permits the classification of the mycobactin being studied as either the P-type or the M-type. For the P-type mycobactins the first fragmentation consists of the loss of the side chain beyond the a,b-double bond whereas the M-type mycobactins lose their cobactin fragment leaving the mycobactic acid part of the parent ion. 5.3 Chromatographic properties In 1968 White and Snow described a method to separate and identify the different mycobactins4,18,21 that utilized isopropan- 2-ol for elution during silica gel thin-layer chromatography of the corresponding aluminum and ferric complexes.The authors found that since the side-chain length does not affect the Rf values the migration depends on the nature of the mycobactin nucleus allowing a separation according to the source mycobacteria. The use methanol–water reversed phase HPLC by Ratledge and Ewing further facilitated characterization35 without requiring pure metal-free mycobactins as in the case of NMR. In contrast to the earlier TLC methods HPLC also allowed separation of mycobactins differing in the unsaturation or the length of the pendant acyl-chain and not only in the nucleus. The power of HPLC was demonstrated by the successful separation of the seven components of mycobactin S.5.4 NMR Although not routinely utilized for mycobactin characterization after extraction another convenient way of identifying myco-bactins is nuclear magnetic resonance of metal-free mycobactins. 32 For all of the mycobactins studied by Greatbanks and Bedford the proton peaks were divided into the same five regions of the spectrum. The aromatic protons absorb in the 7.7–6.5 ppm region; the olefinic protons the protons a to an oxygen atom and the protons a to two groups such as a nitrogen atom or a carbonyl group are between 6.0 ppm and 4.0 ppm. Protons a to a nitrogen atom appear at 4.0–3.0 ppm and allylic protons at 3.0–2.0 ppm. They established a simple scheme (Scheme 2) allowing for convenient characterization of several mycobactins based on well-defined peaks characteristic of the different mycobactins.Scheme 2 Identification of mycobactins by NMR. Mycobactins F S T R H A and P can be identified via their NMR spectra by simple observation of the presence or absence of well-defined peaks (Reproduced by permission from D. Greatbanks and G. R. Bedford Biochem. J. 1969 115 1047). Combination of all these methods constitutes a precise fingerprinting method for the identification of the mycobactins. 36 Combined with efficient ways of producing and purifying mycobactins,27,31 these techniques make it possible to apply Snow’s suggestion of utilizing mycobactins as chemotaxonomic markers for mycobacteria. Indeed as different strains of mycobacteria produce different mycobactins two strains of mycobacteria producing structurally close mycobactins will be considered taxonomically related.The combination of TLC and HPLC led to the development by Hall,31 of an efficient method of identification of mycobactins. Mycobactin analysis was successfully applied in 1985 to the classification of armadillo-derived mycobacteria37 and in 1992 to the identification by Bosne and Levy-Febrault of M. fortuitum and M. chelonae subspecies (Table 2).38 Table 2 Sources of known mycobactins Source Mycobactin M. phlei M. tuberculosis (and M. bovis M. africanum) M. smegmatis (and M. Clitzky M. Gerston) M. thermoresitible and M. fortuitum M. aureum M. terrae M. fortuitum (and M. farcinogenes M. senegalense) M.marinum M. marinum M. paratuberculosis M. kansaii P T S H A R F M N J and ‘J’ K The identification of mycobacteria through the types of mycobactins produced was also adapted to facilitate clinical identification of mycobacteria. In order to propose a medical treatment it is of particular importance to be able to quickly identify the specific mycobacterial cause of an infection since different strains of mycobacteria have different responses to antibiotics. The method developed by Barclay Furst and Smith was based on TLC of 55Fe labeled mycobactins.26 The characterization could be done from 1 to 5 days depending on the isolated strain facilitating clinical identification of mycobacteria. A non-mycobactin based methodology for routine identification of mycobacteria is the GC analysis of the microbial fatty acids and mycolic acid cleavage products.39–42 Therefore joint analyses of mycobactins and mycolic acids by TLC developed in 1995 by Leite et al.afforded a simple test for the clinical identification of mycobacteria.43 6 Synthesis of mycobactins and mycobactin analogs After detailed studies Snow suggested that alternate or modified forms of mycobactins might serve as antagonists of mycobacterial growth by competitively binding the iron and/or inhibiting its assimilation by targeted forms of mycobacteria and thus might be of therapeutic value.4 Additionally design and synthesis of mycobactin analogs that contain potential ‘drug linkers’ may provide a new class of therapeutic agents.Direct attachment of antimicrobial agents to the analogs may allow the pendant drug to be targeted to mycobacteria. The importance of all these possible therapeutic applications initiated considerable interest in the total syntheses of mycobactins and analogs. A retrosynthesis for mycobactins was proposed44 based on the products of their chemical degradation. As shown in Scheme 3 disconnection of the ester bond of mycobactins 1 gives two fragments mycobactic acids 2 containing the acyclic hydroxamate residue and cobactins 3 containing the cyclic hydroxamate residue. Further disconnections of the amide bonds in fragments 2 and 3 result in four corresponding components oxazolines 4 hydroxamic acids 5 b-hydroxy acids 6 and Nehydroxycyclo-l-lysine 7.This section will present methods for the preparation of these fragments and/or protected versions of them. 6.1 Synthesis of oxazoline derivative 4 All syntheses reported so far related to the oxazoline fragment 4 focused on the core structure represented by compound 11 i.e. residue 4 with R2 = R3 = H corresponding to the synthesized mycobactins T and S. In 1972 St. C. Black and Wade reported several methods for the preparation of protected forms of 2-(2A-hydroxyphenyl)- 4,5-dihydrooxazole-4-carboxylic acid 11.45 Because of the stability of the oxazoline ring to mild hydrolytic conditions the first method employed by the authors was the hydrolysis of a corresponding ester (14 in Scheme 4). They prepared esters of type 14 by reaction of serine ester hydrochlorides 13 with ethyl 2-hydroxybenzimidate 12.This sequence allowed for the synthesis of an optically active oxazoline but the overall yield was not high (55%) and starting material 12 was formed from 2-hydroxybenzonitrile via its hydrochloride salt in only 27% yield. An alternative route involving cyclization of hydroxy amide 17 was accomplished by the same authors (Scheme 5). Amide 17 was obtained in high yield by the reaction of 2-hydroxybenzoyl azide 15 with serine 16 followed by conversion to the isopropyl ester. Cyclization by reaction with thionyl chloride afforded oxazoline ester 14a. While this second route seemed suitable for a high-yield synthesis of oxazolines unfortunately the use of a strong base in the preparation of 17 led to racemization.Eventually a milder procedure was investigated involving the treatment of the bis-p-toluenesulfonyl (tosyl) derivative 18 with base to give the tosyl oxazoline 19 which afforded the desired oxazoline acid 11 in 19% yield after hydrolysis (Scheme 6). These results constituted a good first approach of the oxazoline synthesis but needed improvements in yield and stereocontrol. 103 Nat. Prod. Rep. 2000 17 99–116 Scheme 3 Retrosynthetic analysis of mycobactins. Scheme 6 Dehydrative cyclization of the corresponding b-hydroxyamide for the preparation of (S)-2-[2-(benzyloxy)phenyl]- 4,5-dihydrooxazol-4-carboxylic acid was reported by Maurer and Miller in 1983 (Scheme 7).46 Thus 2-benzyloxybenzoic acid 20 was coupled with the methyl ester of l-serine 21 using dicyclohexylcarbodiimide (DCC) or 2-ethoxy-N-(ethoxycarbonyl)-1,2-dihydroquinoline (EEDQ).The optically pure oxazoline 23 was formed by treating the hydroxy amide 22 with SOCl2 at 215 °C in THF. Scheme 4 Scheme 7 Scheme 5 Eventually Hu and Miller developed another method using Burgess’s reagent for the cyclization of amide 24 (Scheme 8).47 2-(Benzyloxy)benzoic acid (20) was coupled with l-serine benzyl ester 13 to afford amide 24 in 90% yield. Treatment of amide 24 with Burgess’s reagent provided oxazoline 25 in 66% Nat. Prod. Rep. 2000 17 99–116 104 yield. This last method appears to be satisfactory as far as convenience and yield are concerned although it requires the preparation of Burgess’s reagent.Scheme 8 6.2 Synthesis of hydroxamic acid units 5 and 7 Mycobactins contain two hydroxamic acid units which are the cobactin ring system 27 and the mycobactic fragment 28 both derived from l-lysine 29. The syntheses of 27 and 28 are closely linked and will be discussed in this section. Early methods reported the synthesis of Ne-hydroxy-dllysine. In 1963 Roger and Neilands achieved the preparation of Ne-hydroxy-dl-lysine in the form of its 2-nitroindane-1,3-dione salt.48 In 1969 reaction of 5-(4-bromobutyl)hydantoin with hydroxylamine by Lancini Lazzari and Diena afforded the synthesis of Ne-hydroxy-dl-lysine.49 Eventually in 1972 St. C. Black Brown and Wade,50 in an attempted formation of the cobactin ring system obtained hydroxylamine 30 by treatment of diethyl 5-bromo-1-phthalamidopentane-1,1-dicarboxylate with benzaldoxime and subsequent transformation of the resulting nitrone to the corresponding hydroxylamine.In 1974 Isowa and Ohmori reported the preparation of optically active Ne-hydroxy-l-lysine 35 by mild deprotection of Ne-tosyl-Ne-benzyloxy-L-lysine 34 (Scheme 9).51 Precursor 34 was obtained by enzymatic resolution of Ne-acetyl-Ne-tosyl-Nabenzyloxy-dl-lysine 33. In 1982 Maurer and Miller described the synthesis of 38 a protected form of Ne-acetyl-Ne-hydroxy-dl-lysine from N-Boce-bromonorleucine benzyl ester 36 (Scheme 10).52 Protected Ne-acetyl-Ne-hydroxy-dl-lysine 38 was prepared by direct alkylation of O-benzyl acetohydroxamate 37 with bromide 36 which gave predominant N-alkylation.In 1993 J. P. Genet et al. applied palladium-catalyzed amination of an allylic ester with (N,O)-bis-Boc protected Scheme 9 Scheme 10 hydroxylamine to synthesize Ne-hydroxy-l-lysine a component of mycobactin T.53 Allyl-l-glycine 39 was functionalized in six steps54 to give allylic carbonate 40 (Scheme 11). The palladium-catalyzed amination of 40 in the presence of (N,O)- bis-Boc-protected hydroxylamine and subsequent deprotection provided Ne-hydroxy-l-lysine dihydrochloride 42. Scheme 11 The first studies related to syntheses of the terminal cyclic hydroxamate of the mycobactins were by St. C. Black Brown and Wade who reported three different approaches reductive cyclization ring expansion and ring oxidation.55 The first route involved reductive cyclization of a hydroxyimino diester by treatment with Fe–HCl.This afforded seven-membered hydroxamic acid 31 but in impure form and very low yield (1.5%). Using a ring expansion strategy the authors synthesized a-bromo cyclic hydroxamic acid 32 in 3% yield from the reaction of the corresponding a-bromocyclohexanone with benzenesulfonohydroxamic acid. Eventually the third strategy involved a ring oxidation. Treatment of an a-bromo lactam with triethylammonium fluoroborate followed by mCPBA afforded pure a-bromo cyclic hydroxamic acid 32 in 3% overall yield. Despite the low yields 32 was considered a precursor to a cobactin. In 1981 Maurer and Miller reported another route to the cobactin ring.56 The carboxyl group of 43 was converted to an O-benzyl hydroxamate by coupling with O-benzylhydrox- 105 Nat.Prod. Rep. 2000 17 99–116 ylamine (Scheme 12). When 44 was treated with a slight excess of triphenylphosphine (PPh3) and diethyl azodicarboxylate (DEAD) intramolecular alkylation took place leading to the desired protected hydroxamic acid 45. Scheme 12 This method required the synthesis and enzymatic resolution of the l-e-hydroxynorleucine precursor of 43 and the subsequent cyclization was complicated by N- vs. O-selectivity. To circumvent these problems in 1995 Hu and Miller applied a direct oxidation57,58 of primary amines by dimethyldioxirane to the synthesis of both hydroxamic acid units of the mycobactins Ne-acetyl-Ne-hydroxy-l-lysine and the seven-membered cyclic hydroxamic acid.Thus esters of Na-Cbz-l-lysine (46) were oxidized by dimethyldioxirane (DMD) to provide nitrones 47 (Scheme 13). Scheme 13 From nitrones 47 both hydroxamic acid units could be prepared. For the synthesis of the linear Ne-acetyl-Ne-hydroxyl-lysine the crude nitrone product was treated with hydroxylamine hydrochloride salt and directly acetylated with acetic anhydride in pyridine in order to avoid isolation of unstable hydroxylamine 48 (Scheme 14). This acetylation afforded Scheme 14 desired hydroxamic acid 49a in a 51% yield along with N,Odiacetylated product and O-acetylated product. Use of palmitoyl chloride in the acylation step produced 50b a key ironbinding component of the mycobactins that contains the natural long acyl group and facilitated the total synthesis of mycobactin S.47 Since the acylation of hydroxylamine 48 also produced byproducts from N,O-diacylation and O-acylation a slight Nat.Prod. Rep. 2000 17 99–116 106 variation was reported by Xu and Miller in 1998.59 Treatment of hydroxylamine 48 with a large excess palmitoyl chloride in the presence of NaHCO3 resulted in complete N,O-diacylation of the hydroxylamine moiety. Subsequent selective removal of the O-palmitoyl hydroxamate group by treatment with Hünig’s base afforded hydroxamic acid 49b cleanly. Treatment of the related hydroxylamine 51 obtained from 47b with DCC DMAP (dimethylaminopyridine) and DMAP·HCl provided the desired cyclic hydroxamic acid 52 which was immediately protected to give compound 53 (Scheme 15).57 Scheme 15 6.3 Synthesis of mycobactic acid 2 With the preparation of oxazoline 4 and linear hydroxamic acid 5 the synthesis of mycobactic acid 2 one of the two major fragments of mycobactins could be realized.Different coupling agents have been used that allow for various functional group protection strategies. In the early synthesis of a non-iron binding mycobactin analog Carpenter and Moore60 coupled dl-2-phenyl-4,5-dihydrooxazoline-4-carboxylic acid 54 with the protected lysine ester 55 in the presence of DCC. Subsequent saponification of the product afforded the desired mycobactic acid analog 56 (Scheme 16). Scheme 16 In the paper by Maurer and Miller,46 the first intention of the authors was to couple the oxazoline fragment 26 (Scheme 8) with amines but all attempts with various coupling agents failed.This result contrary to the coupling realized by Carpenter and Moore was attributed to the presence of the bulky benzyloxy group on the phenyl ring. Thus instead of forming the oxazoline before coupling as originally suggested acyclic dipeptide 59 was assembled in high yield (92%) by coupling of 57 and 58 with EEDQ in chloroform (Scheme 17). Compound 59 was subsequently cyclized in the presence of SOCl2 at –15 °C to give the oxazoline peptide 60 as a pure (S,S)- diastereoisomer. In 1997 Hu and Miller removed the benzyl-protecting group of the oxazoline before the coupling with amine 63.47 The coupling of oxazoline acid 62 with hydroxamic acid 63 using [1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride] (EDC) afforded mycobactic ester 65 in 59% yield (Scheme 18).This confirmed the hypothesis that the presence of a large benzyloxy group in acid 26 was a major factor in the failure of the initial coupling attempts. Conditions developed by Xu and Miller allowed the coupling of the oxazoline 62 in the presence of EDC and 1-hydroxy-Scheme 17 Scheme 18 7-azabenzatriazole (HOAt) with amine 64 containing a free hydroxamic acid.59 The desired coupling product 66 was formed in 91% yield confirming the author’s hypothesis that on the basis of pKa values coupling reactions can be carried out under finely tuned conditions without masking certain functional groups.Thus effective syntheses of mycobactic acids have been developed. 6.4 Synthesis of cobactin 3 and analogs Different preparations of cobactin the second major fragment of mycobactin are described in this section. Carpenter and Moore initiated studies with synthesis of 69,60 again a non-iron chelating analog of cobactin T by coupling of dl-3-aminohexanolactam 68 with dl-3-hydroxybutyric acid hydrazide 67 in the presence of HNO3 which generates an intermediate acylazide (Scheme 19). After isolation of azopine derivative 70 Maurer and Miller synthesized protected cobactin T 74 46 by EEDQ-mediated coupling of 70 and d-b-hydroxybutyric acid 73 (Scheme 20). Scheme 19 Scheme 20 Subsequently Hu and Miller utilized a modified route in which amine 71 was coupled with (R)-3-hydroxybutyric acid (73) in the presence of DCC DMAP DMAP·HCl to provide OTBDPS (tert-butyldiphenylsilyl) protected cobactin T 75 in 63% yield.47 For the synthesis of mycobactin analogs with synthetic variation of the normal b-hydroxybutyrate component,59 four different cobactin derivatives were targeted.First free cobactin analogs 78 and 79 were prepared in 95% yield by coupling cyclolysine 72 and Cbz-protected-l-serine 76 (or Cbz-protected l-threonine 77) in the presence of EDC and HOAt (Scheme 21). Using HOAt over other traditional coupling additives provided significant enhancement of the reaction rate and yield while minimizing side reactions. Scheme 21 The same coupling conditions were used to couple amine 71 with carboxylic acids 80 or 81 in order to prepare protected cobactins 82 in 97% yield or 83 in 91% (Scheme 22).Scheme 22 6.5 Synthesis of mycobactin 1 and analogs Coupling of the two main fragments mycobactic acid and cobactin by an ester linkage afforded the natural mycobactins. Alternate incorporation of an amide linkage provided novel mycobactin analogs. Both approaches have been investigated and are discussed here. The route chosen by Carpenter and Moore for the synthesis of the non-chelating analog of mycobactin actually differs from the usual coupling between a mycobactic acid and a cobactin 107 Nat. Prod. Rep. 2000 17 99–116 fragment.60 Indeed they realized the coupling of fragments 56 and 69 by an ester bond in the presence of the coupling agent carbonyl diimidazole (CDI) and then attached the lipophilic C18 side-chain (Scheme 23).This route afforded desired mycobactin analog 84. Scheme 23 In 1983 the first total synthesis of an iron chelating mycobactin mycobactin S2 was reported by Maurer and Miller (Scheme 24).46 The product differed from natural mycobactin S by replacement of the long acyl chain by an acetyl group. But all of the chiral centers of mycobactin S were incorporated. The synthesis was performed in a convergent manner by forming the ester linkage between mycobactic acid 85 and cobactin 87 using the PPh3–DEAD-mediated ester bond formation. This method allowed incorporation of the correct stereochemistry at the ester linkage by inversion of the hydroxyl group of the bhydroxybutyrate component during the coupling.The protected mycobactin S2 (89) was isolated in 50% yield with the correct (S,S,S,S)-configuration corresponding to mycobactin S. The same Mitsunobu conditions were utilized during the synthesis of mycobactin S by Hu and Miller,47 where protected mycobactin S 90 was obtained in 49% yield by coupling 86 and 88. Scheme 24 Eventually Xu and Miller developed an improved synthetic approach which increased the overall chemical yield by Nat. Prod. Rep. 2000 17 99–116 108 circumventing unproductive protection and deprotection steps.59 Both ester and amide linkages between mycobactic acid 91 and cobactin analogs 92–95 were separately generated using EDC and HOAt (and DMAP in the cases of 94 95) (Scheme 25).Under these conditions coupling reactions in the presence of the free hydroxamic acid and/or the free phenolic hydroxy group consistently proceeded in excellent yields. Subsequent deprotection provided the target compounds. Scheme 25 7 Isolation and characterization of exochelins and carboxymycobactins In 1975 the search for an extracellular iron-binding compound produced by mycobacteria able to solubilize iron under physiological conditions led to the discovery of a new siderophore differing from mycobactins. From the nonpathogenic M. smegmatis Macham and Ratledge isolated a water-soluble iron-binding agent,61,62 whose structure was not completely determined but was found to be a polypeptide.The hypothesis of the authors was that it was a new extracellular siderophore that they called exochelin MS. The same year the same authors isolated another extracellular siderophore from the pathogenic M. bovis.63 Comparing exochelin MB from M. bovis and exochelin MS from M. smegmatis they noticed differences in properties related to extraction by organic solvents. Subsequently various extracellular iron-binding agents were isolated from both pathogenic and non-pathogenic strains of mycobacteria. Extracellular siderophores were isolated from M. avium in 1977,64 from M. avium M. intracellulare M. scrofulaceum and M. paratuberculosis in 198365 and from M. vaccae in 1986.66 In 1988 exochelins were isolated from M.tuberculosis M. bovis and M. africanum67 but were found to be the same as those previously known. All of these siderophores were extracted from microorganisms grown under iron-deficient conditions and purified by combination of ion-exchange chromatography and HPLC. It was only in 1995 twenty years after the discovery of the first exochelin that the structures of these extracellular siderophores were elucidated. Sharman Williams Ewing and Ratledge characterized both exochelins MS 102,68 from M. smegmatis and exochelin MN 103,69 from M. neoaurum. They are both polypeptides (Scheme 26). Exochelin MS is a formylated pentapeptide with unusual linkages between the amino acid components of the molecule. This absence of conventional peptide bonds suggests potential evolutionary design of resistance to peptidase-mediated hydrolysis.Exochelin MN is a unique hexapeptide that contains a b-hydroxyhistidine residue found in only one other siderophore. Scheme 26 Exochelins MS 102 and MN 103. The structures of extracellular siderophores isolated from pathogenic mycobacteria M. avium70 and M. tuberculosis29 also were reported in 1995 and called carboxymycobactins. They were found as mixtures of compounds whose structures differ radically from the peptide exochelins isolated from nonpathogenic mycobacteria but share a common core with the structure of their intra-cellular counterparts the mycobactins Scheme 27 Structure of carboxymycobactins isolated from M. avium 104 M. tuberculosis 105 and M.smegmatis 106. (Scheme 27). However they are smaller than mycobactins because of a shorter saturated or unsaturated side chain (R1) which usually terminates in a carboxylic acid or an ester.71 (This apparently depends on the length of the culture of the microorganism.)72 The modified side chain induces greater hydrophilicity to carboxymycobactins and accounts for their occurrence in aqueous extracellular media. The structures of mycobactins and carboxymycobactins were so similar that Gibson Horwitz et al. suggested that their core structure is synthesized by the same set of enzymes and that only one of the final steps determines if a mycobactin or a carboxymycobactin is produced.29 All of the structure elucidations of extracellular siderophores were accomplished by a combined application of derivatization MS and GC analyses and modern NMR techniques which even allowed the determination of the threedimensional structures in some cases.Thus extracellular siderophores synthesized by mycobacteria appeared to be of two different types the water-soluble polypeptides synthesized by non-pathogenic strains and the chloroform-extractable mycobactin-like siderophores called carboxymycobactins from pathogenic strains of mycobacteria. However in 1996 a carboxymycobactin was isolated from nonpathogenic strains of M. smegmatis as a second extracellular siderophore.73 Its ‘mycobactin-like’ structure was confirmed in 1998. The proportion of carboxymycobactin to the total amount of siderophores produced by M.smegmatis was estimated to be 5–10%. It is also interesting to note that the production of any of the three types of siderophores was maximal at the same iron concentration in the media. Eventually this last discovery eliminated the possibility that mycobacterial virulence was directly correlated with the presence of carboxymycobactins. The respective role of these three different iron-binding agents occurring in mycobacteria will be discussed in a following section. It should be noted that the literature can be confusing with regards to the terms exochelins and carboxymycobactins. Prior to the structural elucidations of the carboxymycobactins all extracellular mycobacterial siderophores were referred to as exochelins independent of their solubility differences.Herein the term carboxymycobactin refers to the water and chloroform soluble extracellular siderophores while exochelin refers to the water only soluble extracellular siderophores. 8 Biosynthesis of mycobactins and exochelins 8.1 Isotopic labeling studies of mycobactin biosynthesis Early biosynthetic studies of the mycobactins were restricted to isotopic labeling experiments. Allen and co-workers demonstrated the incorporation of [U-14C]-l-lysine into the cobactin and mycobactic acid fragments of mycobactin P. Suprisingly 17% of the mycobactic acid radioactivity was found in the serine of the oxazoline ring.74 The authors offered no explanation for the radioactive serine except that complete degradation of the radiolabeled lysine was unlikely.Tateson further demonstrated nearly equal incorporation of [U-14C]-l-lysine into both cobactin and mycobactic acid by M. phlei and M. smegmatis.75 Ne-Hydroxy-[U-14C]-l-lysine was not taken up by the cells and no conclusion as to a common hydroxylamine intermediate for the cyclic and linear hydroxamic acids could be made. Incubation of M. phlei and M. smegmatis with [2-14C]propionate and [1-14C]acetate respectively yielded high radioactivity in the cobactin linker fragments of the two mycobactins. Isotopic labeling studies on the aromatic region of mycobactin S were performed using [G-14C]-shikimic acid which led to the radiolabeling of the mycobactic acid and also to the extracellular salicylic acid excreted by M.smegmatis.76,77 Treatment of the same strain of mycobacteria with [carboxy- 14C]salicylic acid led to the incorporation of a radioactive salicylic acid moiety into mycobactin S. This demonstrated salicylate uptake by mycobacteria and its intermediacy in the biosynthesis of salicylate-containing mycobactins.78 The salicylic acid incorporated into the mycobactins has its origin through a chorismate to isochorismate to shikimate pathway.79 The 6-methylsalicylic acid-containing mycobactins (e.g. mycobactin P) do not utilize this pathway as shown by the failure to incorporate radiolabeled salicylic acid into the lipophilic siderophore and are thought to employ a polyketidebased biosynthesis of the aromatic moiety.80 No isotopic labeling studies involving the biosynthesis of the exochelins have been reported.109 Nat. Prod. Rep. 2000 17 99–116 8.2 Identification of gene clusters encoding for biosyntheses of mycobactin T and exochelins of M. smegmatis With the genome of M. tuberculosis H37Rv sequenced,81 Cole et al. postulated that a 24 kilobase region contained the mycobactin biosynthetic (mbt) genes. Further studies on this mbt gene cluster by Walsh and co-workers82 allowed for a more detailed proposal for the biosynthesis of mycobactin T. The gene cluster designated mbtA-J contains ten open reading frames. The proposed gene products are isochorismate synthase acetyl hydrolase salicylate-AMP ligase polyketide synthase lysine-N-oxygenase phosphopantetheinyl (PPT) transferase and non-ribosomal peptide synthetase.The nonribosomal peptide bond biosyntheses are thought to be mediated by the post-translational modification of aryl and peptide carrier proteins with PPT transferase. This would generate thioesters as the activated intermediates necessary to form the mycobactin peptide framework. The presence of genes encoding for isochorismate synthase salicylate-AMP ligase and polyketide synthases confirmed the isotopic labeling studies mentioned previously. It is unknown whether lysine-N-oxygenase oxidizes the terminal amine of the lysine residues before or after incorporation into mycobactin T. A proposed linear biosynthesis is initiated with salicylic acid and terminated with an intramolecular lactamization forming the cyclic hydroxamic acid.The authors were able to express four of the genes in E. coli and reveal the formation of a salicylate-aryl carrier protein complex mediated by a PPT intermediate. The genetic basis for exochelin biosynthesis has also been studied in M. smegmatis.83 Deletion studies revealed the presence of a formyl transferase gene designated fxbA as necessary for exochelin biosynthesis. Two genes fxbB and fxbC homologous with known peptide synthetase genes were identified in the same cluster.84 The presence of an exiT gene encoding for a putative ABC transporter suggests that it assists the transport and excretion of the exochelin from the cell.85 Thus as with mycobactin T a non-ribosomal-mediated synthesis of the peptide-based exochelin was postulated.An iron dependent mycobacterial ideR protein may regulate exochelin biosynthesis in M. smegmatis.86 An ideR mutant demonstrated derepressed exochelin biosynthesis under iron sufficient conditions. 9 Iron transport mechanisms in mycobacteria 9.1 Introduction The following section will discuss the current understanding and proposed models of the complex iron transport mechanisms (ITMs) in mycobacteria. Microbial iron acquisition has been extensively studied and reviewed.3 Three general mechanisms have been recognized. Chelation of extracellular iron by siderophores is followed by recognition and transport of the ferrisiderophore complex. This process has been shown to involve receptor proteins. Siderophore biosynthesis and expression of the receptor proteins are regulated by the presence/absence of iron.The two other processes involve low-affinity ferric-transport directly from host iron sources and Fe(iii) reduction to Fe(ii) prior to transport. Chelation and low affinity transport mechanisms have been proposed for mycobacteria. No evidence for the reductive transport has been found. It is well known that biologically essential Fe(iii) is insoluble under physiological conditions. Acquisition of iron by mycobacteria depends on the presence of soluble Fe(iii) complexes generated from host iron sources. This solubilized Fe(iii)- complex must then be sequestered by the mycobacteria and transported across the cell envelope to be utilized immediately or stored for future metabolic need.As will be discussed below the ITM utilized by a particular strain of mycobacteria seems to Nat. Prod. Rep. 2000 17 99–116 110 be determined by the soluble iron chelator-Fe(iii) complex and the pH of the extracellular environment. ITMs have been proposed involving ferric salicylate ferric citrate and ferriexochelins/ carboxymycobactins. Additional involvement of membrane bound proteins also have been examined and will be discussed. Scheme 28 updated and adapted from the one developed by Ratledge,5 represents the proposed modes of iron transport employed by these microbes. The involvement of two structurally distinct peptide based siderophores is fairly unique for microbial iron transport. Many of the processes shown have not been definitively proven demonstrating the necessity for more intense research in this area.Scheme 28 Iron transport in mycobacteria involving siderophores. A potential pitfall in the study of these ITMs is the use of in vitro mycobacterial systems. In order to obtain detectable amounts of mycobacterial siderophores in vitro studies have been consistently carried out under iron deficient conditions. Any results obtained from these studies will be difficult to correlate to the ITM of in vivo mycobacterial infections. Mycobacterial infections occur in the macrophages of host tissue and the state of iron sufficiency/deficiency and pH in the macrophages are not definitively known and may diminish any correlation between in vitro/in vivo ITMs. 9.2 Mycobactin in the cell envelope Mycobactins lipophilic water insoluble siderophores (iron complex Ks ~ 1036) are membrane bound iron chelators as determined by electron microscopy.87 Ratledge demonstrated their involvement in an ITM of M.smegmatis through radioactive 55Fe-mycobactin uptake.88,89 Their water insolubility precludes their being extracellular iron chelators. The role of mycobactins in vivo is not certain. Mycobactins have not been isolated from infections of M. leprae in armadillo liver,90 M. tuberculosis in mouse spleen M. avium from flamingo liver and spleen and M. paratuberculosis in bovine ileum.91 This absence may be due to many factors. The pH of the phagocytic vacuoles lies somewhere between 4.5 and 6.0. Lambrecht proposed that this pH range may allow for the dissociation of iron from some host iron carrier proteins generating a state of iron sufficiency thus eliminating the need for mycobactins.The relationship between the stage of an infection and iron sufficiency/deficiency is not known and the lack of any detectable mycobactins does not necessarily mean they were never involved in iron transport. They may be produced at an early stage of the infection and then degraded when a state of iron sufficiency was reached. Furthermore the infecting cells may not have had homogenous access to iron in vivo and different pockets of mycobacteria could be either iron deficient or sufficient. 9.3 Iron sequestration and transport utilizing salicylate Prior to growth M. smegmatis releases salicylic acid into the extracellular environment.Investigation into its role as an iron chelator mediating the transfer of iron to the lipid bound mycobactin was then studied.92 It was discovered that there is no ferric salicylate in the extracellular medium in the presence of phosphate ions. A model system was developed in which mycobactin was suspended in n-octanol as a lipid surrogate. Transfer of iron was efficiently accomplished. Since the phosphate concentration in macrophages is not known the possibility exists that salicylate may be an extracellular ironsequestering agent that transfers iron to mycobactin in the cell envelope. 9.4 Iron sequestration and transport utilizing citrate Citric acid is known to exist in human serum and also participates in the transfer of iron to and from transferrin.Thus it was examined as a participant in the ITM of M. smegmatis.93 Iron deficient and sufficient washed cell suspensions took in iron from the citrate complex without incorporating the citrate itself as seen through radiolabeling studies. The uptake of iron was unaffected by the addition of ferriexochelin and ferric salicylate. Biosyntheses of the exochelin and mycobactin S were unaffected by the presence of ferric citrate. These data suggest a distinct ITM. M. tuberculosis also readily acquired iron from ferric ammonium citrate.94 Mössbauer and EPR studies on whole cells provided evidence for the transient formation of ferrimycobactin in the membrane of M. smegmatis upon treatment with ferric citrate.This provided the first direct evidence for transfer of iron from extracellular ferric citrate to the membrane bound mycobactin. 95 9.5 Iron sequestration and transport utilizing exochelins The discovery of extracellular water-soluble mycobacterial siderophores the exochelins (iron complex Ks ~ 1025) initiated research into ITMs involving sequestration of iron by these compounds. Participation of the exochelins in an ITM necessitates their ability to remove Fe(iii) from host iron sources. Growth of M. smegmatis in serum containing transferrin was enhanced by the addition of exochelins. Furthermore these compounds were able to remove iron from ferritin at rates comparable to ethylenediaminetetraacetic acid (EDTA) and desferrioxamine.63 Additional evidence for exochelin-mediated transport of iron is found in the ability of M. smegmatis to grow with the extracellular iron sources ferritin or ferric phosphate contained in diffusion capsules.62 Inoculation with exochelin MS increased the rate of iron uptake in M. smegmatis after the fourth day.96 When the exochelins were discovered an ITM was proposed in which the exochelins act as extracellular iron scavengers migrate to the cell wall and transfer iron to the mycobactins. Attempts to prove this model resulted in two ITM models one of which does not involve mycobactin.97,98 Under conditions of low exochelin concentration M. smegmatis utilizes an energycoupled transport process inhibited by electron transport inhibitors uncouplers of oxidative phosphorylation and thiol reagents.This high affinity process apparently does not require mycobactin and entails direct transport of the ferriexochelin complex into the cell envelope. This view is supported by the lack of ferric-salicylate inhibition of ferriexochelin iron uptake and the existence of M. vaccae R877R that excretes exochelins but does not produce mycobactins.66 Further indirect evidence is found in the absence of any signals corresponding to ferrimycobactin in the membrane of M. smegmatis when examined by Mössbauer and EPR spectroscopy after treatment with the xenosiderophore hexapeptide ferricrocin.95 With elevated ferriexochelin concentrations a low affinity passive ITM was postulated by Ratledge.This process was inhibited by the presence of ferric salicylate and thus a mechanism involving iron transfer from ferriexochelin to mycobactin was assumed. Morrison proposed an alternative role for the exochelins in 1995.99 Due to their release late in the growth phase of the mycobacteria when iron demand is diminished iron scavenging by the exochelins for iron transport may not be necessary. The exochelins as secondary metabolites were postulated to be iron stress exhaustion peptides that are synthesized and excreted only to be recycled by the mycobacteria to delay cell death. 9.6 Iron sequestration and transport utilizing carboxymycobactins Relatively little research has been conducted on an ITM utilizing the carboxymycobactins water and chloroform soluble siderophores.It has been shown that these extracellular siderophores promote the growth of three strains of M. tuberculosis albeit slower than the exochelin promoted growth rate of M. smegmatis.96 In 1996 a study by Gobin and Horwitz demonstrated the removal of iron by purified carboxymycobactin from human iron carriers.94 In either 4+1 or 1+1 ratios 95% and 40% saturated human transferrin irreversibly donated iron to the carboxymycobactins and the same was true with iron lactoferrin. Saturation occurred at a maximum time of 3 hours. Much slower rates of iron transfer were found with the incubation of the carboxymycobactins with horse ferritin which required 2 days for saturation to occur. The same report revealed that incubation of M.tuberculosis cultured under iron deficient conditions with ferricarboxymycobactin promoted eight times more iron uptake relative to the control. The cells also did not obtain iron from human transferrin without exogenous ferricarboxymycobactin. Different ITMs may be present in virulent as opposed to nonvirulent mycobacteria based on the exclusive production of exochelins by non-virulent species and the production of carboxymycobactins by virulent species with the exception M. smegmatis.72,73 While chloroform-soluble carboxymycobactins from M. intracellulare and M. bovis promoted the growth of M. smegmatis a lack of growth promotion was found in M. intracellulare and M. bovis by the water soluble exochelins of M. smegmatis.100 9.7 Iron regulated envelope proteins as possible receptors for extracellular ferrisiderophores In 1987 Ratledge and co-workers noted the expression of 180 kDa 84 kDa 29 kDa and 25 kDa proteins in M.smegmatis under iron deficient conditions but not under iron sufficient conditions.101 They were termed the iron regulated envelope proteins (IREPs). Antibodies raised against the 29 kDa IREP inhibited exochelin-mediated iron uptake by 70% in iron deficiently grown cells and had no effect against cells grown in iron sufficient conditions. The expression of the IREPs and the biosynthesis of exochelins and mycobactins in M. neoaurum were maximized with iron concentrations below 0.5 mg mL21.102 The 29 kDa IREP of M. smegmatis was shown to associate with exochelin MS by affinity chromatography but isolation of the complex was hindered by the concomitant denaturation of the protein.103 Virulent strains of mycobacteria also express IREPs under iron deficient conditions in vitro and in vivo suggesting a role for these proteins as receptors for ferricarboxymycobactins.104,105 The in vivo studies revealed the presence of proteins that were expressed only under iron sufficient conditions in 111 Nat. Prod. Rep. 2000 17 99–116 vitro. This led Ratledge to propose that the state of iron concentration during the course of an infection fluctuates between iron sufficiency/deficiency and the presence of both types of envelope proteins can then be expected. Further studies need to be carried out to fully elucidate the role these proteins play in iron transport especially the 29 kDa IREP found to associate with exochelins of M.smegmatis that also is expressed in vivo from M. avium and M. leprae. Matzanke and co-workers tested growth promotion in M. smegmatis and M. fortuitum with various non-mycobacterial xenosiderophores.95 Many xenosiderophores similar in structure and iron chelation ability differed markedly in their promotion of mycobacterial growth. The authors concluded that the uptake process is not diffusion controlled but mediated by protein receptors. 9.8 Iron release and storage in mycobacteria For ITMs that utilize mycobactins it is necessary to release the iron from the lipophilic siderophore for metabolic use or further storage.Ratledge and co-workers reported NADPH dependent ferrimycobactin reductase activity from the extracts of M. smegmatis.106,107 The authors proposed that the reductive release of Fe(ii) was followed by complexation with salicylate and then used for whatever need was present in the cell. Cell extracts from other organisms (E. coli and Candida utilitis) were able to perform the same transformation thus indicating that a single enzyme may not be responsible for the reduction in mycobacteria. The presence of non-mycobactin-mediated ITMs led Ratledge to propose an iron storage role for mycobactins.97,98 The recent evidence for and discovery of iron storage proteins such as bacterioferritin in three species of mycobacteria (M. leprae,108,109 M.smegmatis,110 and M. avium111) may require a revision of this model. Furthermore the previously mentioned Mössbauer and EPR studies on whole cells of M. smegmatis upon treatment with ferric citrate revealed a transient existence of the ferrimycobactin intermediate and the rise of spectroscopic signals consistent with the presence of bacterioferritin stored iron.95 The presence of iron storage proteins in mycobacteria may explain the failure to isolate mycobactins in vivo. If a state of iron sufficiency existed when the tissues were isolated for mycobactin extraction iron saturated bacterioferritin may have triggered degradation of the mycobactins and repressed their biosynthesis. The presence of bacterioferritin in mycobacteria led Morrison to propose a cell to cell transport of iron.99 Mycobacteria as close packed colonies and mats could be linked by linear networks of mycobactins.This network could mediate reversible non-aqueous intercellular iron transport from the bacterioferritin of one cell to another. 10 Possible therapeutic applications of mycobacterial and mycobacterial-like siderophores targeting the iron uptake mechanisms of mycobacteria 10.1 Introduction The previous section highlighted the complexity of the iron transport mechanism in mycobacteria. The plethora of mechanisms available for the acquisition and storage of iron both known and possibly unknown emphasizes the necessity of this metabolic nutrient for mycobacterial survival and reproduction. Furthermore the course of microbial infection depends on the competition for iron between the host and microbe.112 Any disruption of mycobacterial iron acquisition may prove to be lethal to the microbes and offer a possible therapeutic regimen for the treatment of mycobacterial infections.A resurgence in the occurrence of tuberculosis (TB) infections worldwide113 and the emergence of drug resistant strains114 re-emphasizes the Nat. Prod. Rep. 2000 17 99–116 112 constant need for research into novel anti-mycobacterial agents. TB is the world’s leading killer among infectious diseases causing 3 million fatalities annually and approximately 2 billion people are currently infected. Coinfection with HIV has contributed to the rapid growth in TB infection rates worldwide.115,116 Other mycobacterial infections also have been found in HIV immuno-compromised patients most notably M. avium.117 New modes of treatment of TB and other mycobacterial infections are clearly necessary. One problem in the treatment of microbial infections is the inability of drugs to diffuse across the cell envelope and reach their intended targets. With mycobacterial infections this difficulty is particularly acute due to the nature of the mycobacterial cell envelope.118,119 The cell membrane is coated with a polymeric complex consisting of peptidoglycans covalently attached to a layer of arabinogalactans terminating with a densely packed array of mycolic acids. Glycolipids have been found to associate with the mycolic acids forming a second bilayer.This overall structure exhibits extremely low fluidity and diffusion of drugs across the envelope can be significantly retarded. Utilizing the siderophores of the mycobacteria and their analogs as a basis for anti-mycobacterial agents may be a means overcoming the drug permeability problem. The so called ‘Achilles’ heel’ in mycobacteria may lie in their metabolism of iron.5 The complexity of iron transport in mycobacteria suggests that targeting a specific aspect of the iron transport mechanism may not be entirely successful because the microbe will adapt by using another means of acquiring iron. This may indeed prove true unless there is a potential therapeutic target common to all the various mechanisms that is absolutely necessary for the mycobacterium’s survival.10.2 Mycobactins and mycobactin analogs as anti-mycobacterial agents Snow’s hypothesis Detailed studies and the structural elucidation of the mycobactins led Snow to suggest and demonstrate that antagonists to the growth of one species of mycobacteria may be found in the naturally occurring mycobactins of another.4 Depressed growth rates of M. paratuberculosis M. kansasii and M. tuberculosis were found when inoculated with either mycobactins M or N. Furthermore treatment of M. paratuberculosis with combinations of mycobactins P and either M or N led to growth rates significantly slower than treatment of the microbes with any of them individually. Although not therapeutically useful the hypothesis was proven.A more recent study on the growth inhibition by natural mycobactins revealed the growth inhibition of M. aurum by ferrimycobactins J and S at concentrations above 5 mM.120 The most striking example validating Snow’s hypothesis is found in recent work by Miller and Hu.47 Synthetic mycobactin S was examined for its effect on the growth of M. tuberculosis H37Rv. Initial studies indicated 99% growth inhibition at 12.5 mg mL21 and subsequently a minimum inhibitory concentration (MIC) of 3.13 mg mL21 was determined! This inhibition is even more intriguing when viewed mechanistically. Mycobactin S and T differ only at the configuration of the methyl group in the butyrate fragment of the mycobactin framework. Assuming that mycobactin S serves as a surrogate for mycobactin T in the iron uptake process it is reasonable to suggest that a very specific recognition event involving ferrimycobactin occurs at some point during iron transport.This event may happen at protein-mediated transfer of extracellularly sequestered iron to the membrane bound mycobactin or at a reductase-mediated transfer of iron to bacterioferritin or salicylate. Metal-analogs of the ferrimycobactins have also received attention as potential inhibitors of mycobacterial growth. Chromic complexes of mycobactin P inhibited the growth of M. paratuberculosis.4 A later study by Barclay and Ratledge found that some inhibition of growth was found relative to ferrimycobactins/ exochelins in M. tuberculosis and M. avium with a variety of non-ferric metal complexes.121 According to Ratledge such an approach as a therapeutic weapon would most likely fail in the long term due to the thermodynamic preference for ferric iron by mycobacterial siderophores over other metal ions.Also the metal ions themselves may prove to be toxic. Synthetic analogs of the mycobactins have also been examined for possible anti-mycobacterial activity. The first example was an analog of mycobactin T lacking the hydroxamic acid and phenolic functionalities needed for iron chelation. 60 The analog demonstrated no appreciable inhibition against M. tuberculosis H37Rv. Impressive results were reported by Miller and Xu in 1998 concerning synthetic mycobactin analogs as inhibitors of M. tuberculosis H37Rv.59 Incorporation of a benzyloxycarbonyl protected serine or threonine in the place the butyrate linker of mycobactin S provided analogs 96 and 97 with 44% and 48% growth inhibition respectively at > 12.5 mg mL21.Analog 100 with b-alanine linker proved to be weakly inhibitory (25% growth inhibition at > 12.5 mg mL21). Suprisingly the Boc protected serine linker with replacement of the ester with an amide linkage provided analog 101 even more potent than mycobactin S with an MIC of 0.2 mg mL21! The enhanced activity of 101 relative to 100 may be attributed to the addition of the bulky NHBoc that induces increased hydrophobicity and/or restricted rotation about the amide bond replacing the naturally occurring ester. The role of hydrophobic groups may be crucial to the development of mycobactin analogs because of their location in the cell envelope of mycobacteria.Snow’s hypothesis has been dramatically proven in the case of the mycobactins by the growth inhibitory activities of mycobactin S and analog 101 against M. tuberculosis H37Rv. Application of Snow’s hypothesis to the exochelins has not been tested since the structures of these extracellular siderophores have only recently been elucidated and no analog syntheses have yet been reported. The literature suggests that use of naturally occurring exochelins of one species of mycobacteria against another may not be successful since mycobacteria recognize such a variety of extracellular iron solubilizers for iron uptake. Synthetic exochelin/ carboxymycobactin analogs may provide useful growth inhibitors although the growth promotion of some species of mycobacteria has been seen with synthetic and natural nonmycobacterial siderophores.95 Thus further research is needed to find more potent mycobacterial siderophore-based inhibitors.Effective synthetic methodology for the mycobactins has set the stage for the generation of a library of analogs. With regards to the exochelins/carboxymycobactins synthetic methodologies need to be developed. Analogs could then be elaborated which target and irreversibly bind to a receptor protein e.g. 29 kDa IREP possibly involved in the transport of the ferriexochelins/ carboxymycobactins. 10.3 Other strategies targeting the iron uptake mechanisms of mycobacteria for possible therapeutic applications The known anti-TB drug p-aminosalicylate (PAS) was originally proposed as an inhibitor of folic acid biosynthesis.Yet it is relatively inactive against other bacteria. Brown and Ratledge studied the mechanism of action of PAS on M. smegmatis.122,123 Their data showed PAS inhibition of iron uptake by 50% at 0.33 mM. Iron dependent enzymes such as glycerol dehydrogenase and NADH-cytochrome c reductase showed reduced activity as well. Finally PAS affects the biosynthesis of mycobactin S. These data suggest that a primary mode of action of this drug is a disruption of the iron acquisition and utilization. Since PAS may partially exert its inhibitory action through a disruption in mycobactin biosynthesis further exploration of agents designed to inhibit the biosynthesis of the mycobacterial siderophores may be a viable route for the development of antiinfectious drugs.Isoiazid a known TB drug forms a covalent complex with an acyl carrier protein AcpM and a b-ketoacyl carrier protein synthase,124 indicating that synthases and carrier proteins involved in the biosynthesis of the mycobacterial siderophores may be possible targets. The use of modified intermediates in the biosynthetic pathway or development of novel inhibitors of the biosynthetic enzymes may reduce the amount of the siderophores present for iron acquisition. Furthermore anti-sense oligonucleotides could also be seen as potential inhibitors by targeting the expression of the previously mentioned biosynthetic genes.All mechanisms proposed for iron transport involve the reduction of Fe(iii) to Fe(ii) for storage and metabolic use. Targeting this reduction would seem to allow for a general antimycobacterial agent that could conceivably be effective independent of the iron transport mechanism utilized. Although this reduction is universal alone it does not represent the ‘Achilles’ heel’ of the mycobacteria. Any inhibitor of the reductase enzyme(s) involved or any of the previously proposed non-siderophore-based inhibitors must still transverse the cell envelope a process that tends to be inefficient in mycobacteria. Siderophore-mediated drug transport targeting the reductive removal of iron may provide a potent and reliable means of treating mycobacterial infections.10.4 Siderophore-mediated drug transport as a means for treating mycobacterial infections Siderophore mediated drug transport has been demonstrated in these laboratories.125–127 Furthermore nature has provided examples of iron transporters used to deliver toxic substances to bacteria in the albomycins,128–132 ferrimycin A1,133,134 and the salmycins.135 Direct attachment of anti-mycobacterial agents to a siderophore is represented in Scheme 29. Scheme 29 General structure of a siderophore–drug conjugate. This conceptually novel approach for the treatment of mycobacterial infections will allow for the generation of conjugates containing drugs targeting the reductase and biosynthetic enzymes mentioned previously anti-sense oligonucleotides and any other agents targeting new gene expression products found from the sequenced genome of M.tuberculosis. Known antibiotics that alone can not diffuse through the dense cell envelope of the mycobacteria could be re-evaluated as siderophore–drug conjugates. Natural and synthetic growth promoting siderophores that participate in iron transport are ideal candidates for the proposed conjugates. These siderophores must contain functionality allowing for rapid and mild synthetic attachment of the linker and drug. Depending on the drug target the linker must be designed for appropriate release from the siderophore. Thus amide linkers could be designed along with chemically labile linkers capable of being non-enzymatically hydrolyzed such as oximes or activated esters.11 Other possible therapeutic applications of mycobacterial siderophores The Fenton reaction is the generation of hydroxyl radicals through the interaction of water and Fe(ii).136 Hydrogen 113 Nat. Prod. Rep. 2000 17 99–116 peroxide and superoxide radicals can initiate Fenton reactions in vivo catalytic in iron(ii).137–139 With no naturally occurring hydroxyl radical scavengers cellular damage can be quite acute and this chemistry is thought to be the cause of reperfusion injury to ischemic organs. Desferrioxamine140 and the synthetic siderophore analogs spermetaxins and spermetaxols,127 are able to inhibit this type of oxidative damage. Carboxymycobactins from M.tuberculosis were examined and patented as cardiac reperfusion injury inhibitors.141,142 Desferricarboxymycobactins were markedly more active than desferroxamine in their ability to preserve systolic and diastolic left ventricular function and blood flow after a period of ischemia in isolated rabbit hearts. Furthermore concentrations of hydroxyl radical produced metabolites and cardiac enzyme lactic dehydrogenase were decreased. Chelation of ferric iron by carboxymycobactins in the cardiac cellular lipid compartments may be the basis for the activity in that lipid oxidation is thought to be a cause of reperfusion injury.143 The use of desferricarboxymycobactins for the treatment of atherosclerosis and vascular injury by prevention of smooth muscle proliferation has been patented.144 Undesired growth of smooth muscle cells plays a key role in the onset of a variety of vascular diseases including atherosclerosis restenosis following angioplasty or other vascular surgeries.Inhibition of this undesired growth could be a means of treatment. The lipid solubility of the carboxymycobactins is thought to impart potent and rapid antiproliferative effects in cell and organ based assays. Another property of the desferricarboxymycobactins is the inhibition of low density lipoprotein cholesterol oxidation that may prevent atherosclerosis. The mycobactins as a structural class of siderophores were originally thought to be exclusively produced by mycobacteria. This has been shown to be false by the isolation of mycobactinlike structures from other microbes.Compounds exhibiting chromatographic properties similar to the mycobactins were isolated from the genus Rhodococcus.145 Ratledge and coworkers isolated mycobactin-like structures from nocardia structurally differing from the mycobactins by the presence of an oxazole rather than an oxazoline ring.146–148 Ratledge and coworkers isolated mycobactin-like structures termed the nocobactins from nocardia structurally differing from the mycobactins by the presence of an oxazole rather than an oxazoline ring.146–148 More recently formobactin from Nocardia sp. strain ND20 exhibited anti-lipid peroxidation activity.149 This mycobactin like compound exhibited an IC50 of 0.65 mM against lipid peroxidation in rat brain homogenate.It also reduced l-glutamate toxicity neuronal cells (EC50 0.017 mM) and suppressed apoptotic cell death by the oxygen radical producer buthione sulfoximine. (EC50 0.072 mM) Scheme 30 These studies suggest that the mycobactins carboxymycobactins and analogs may possess potent anti-oxidative activity due to their lipid solubility and ability to chelate iron(iii). Nat. Prod. Rep. 2000 17 99–116 114 Antitumor activity has been found in the BE-32030 A-E isolated from Nocardia sp. A32030150 and the amamistatins A and B from an actinomycete.151 Scheme 31 A patent reported the growth prevention and destruction of T47D-YB human breast cancer cells grown in vitro upon treatment with the carboxymycobactins of M.tuberculosis.152 50 mM of carboxymycobactin resulted in a seven-fold reduction in growth and 90% destruction of the cancer cells with substantial shift to a low percentage of cells in the growth phase after four days. Mechanistically this activity was not examined but the authors concluded that iron chelation was only partly responsible for the anti-cancer activity. This conclusion was reached due to activity exhibited by ferricarboxymycobactin although it was substantially less potent than the desferri form. The significance of iron acquisition in tumor growth promotion or inhibition is beginning to be explored.153–155 The antitumor activities of these mycobactin like compounds suggest that studies concerning antitumor activity of the siderophores of the mycobacteria and their synthetic analogs are merited.The siderophores of the mycobacteria and analogs may possess a myriad of useful biological activities that either promote or inhibit processes involving iron. They could also be useful probes for elucidating the role of ferric iron in biological systems. 12 Conclusion Mycobactins exochelins and carboxymycobactins represent a fascinating class of microbial siderophores. Much is known but much more needs to be uncovered concerning their role in mycobacterial iron transport. Their simple ability to tightly bind ferric iron could lead to numerous therapeutic applications requiring additional synthetic and biological study. 13 Acknowledgments We gratefully acknowledge grant GM-25845 from the National Institutes of Health and the University of Notre Dame for support of our siderophore research.Scheme 32 14 References 1 Iron Transport in Microbes Plants and Animals eds. G. Winkelmann D. van der Helm and J. B. Neilands VCH Weinheim FRG 1987 and references therein. 2 R. C. Hider Structure and Bonding 1984 58 25. 3 M. L. Guerinot Ann. Rev. Microbiol. 1994 48 743. 4 G. A. Snow Bacteriol. Rev. 1970 34 99. 5 P. R. Wheeler and C. Ratledge in Tuberculosis Pathogenesis Protection and Control ed. B. R. Bloom American Society of Microbiology Washington DC 1994 353. 6 C. Ratledge in Iron Transport in Microbes Plants and Animals eds. G. Winkelmann D. van der Helm and J. B. Neilands VCH Weinheim 1987 p. 207. 7 C.Ratledge Microbiol. Ser. 1984 15 603. 8 F. W. Twort and G. L. Y. Ingram Proc. R. Soc. London Ser. B Biol. Sci. 1912 84 517. 9 J Francis J. Madinaveitia H. M. Macturk and G. A. Snow Nature (London) 1949 163 365. 10 J. Francis H. M. Macturk J. Madinaveitia and G. A. Snow Biochem. J. 1953 55 596. 11 G. A. Snow J. Chem. Soc. 1954 2588. 12 G. A. Snow J. Chem. Soc. 1954 4080. 13 G. A. Snow Biochem. J. 1965 94 160. 14 J. Marks J. Pathol. Bacteriol. 1953 66 151. 15 J. Marks J. Pathol. Bacteriol. 1954 67 254. 16 G. A. Snow Biochem. J. 1961 81 4P. 17 G. A. Snow Biochem. J. 1965 97 166. 18 A. J. White and G. A. Snow Biochem. J. 1968 108 593. 19 R. M. Hall and C. Ratledge J. Gen. Microbiol. 1985 131 1691. 20 R. Barclay D. F. Ewing and C. Ratledge J.Bacteriol. 1985 164 896. 21 G. A. Snow and A. J. White Biochem. J. 1969 115 1031. 22 A. J. White and G. A. Snow Biochem. J. 1969 111 785. 23 R. S. Merkal and W. G. McCullough Curr. Microbiol. 1982 7 333. 24 R. S. Merkal W. G. McCullough and K. Takayama Bull. Inst. Pasteur (Paris) 1981 79 251. 25 W. G. McCullough and R. S. Merkal Curr. Microbiol. 1982 7 337. 26 R. Barclay V. Furst and I. Smith J. Med. Microbiol. 1992 37 286. 27 R. M. Hall and C. Ratledge FEMS Microbiol. Lett. 1982 15 133. 28 S. Bosne F. Papa S. Clavel-Sérès and N. Rastogi Curr. Microbiol. 1993 26 353. 29 J. Gobin C. H. Moore J. R. Reeve Jr. D. K. Wong B. W. Gibson and M. A. Horwitz Proc. Natl. Acad. Sci. USA 1995 92 5189. 30 C. Ratledge in CRC Handbook of Microbiology 2nd edn eds.A. I. Laskin and H. A. Lechevalier CRC Press Boca Raton 1982 Vol. IV p. 575. 31 R. M. Hall Actinomycetes 1986 19 92. 32 D. Greatbanks and G. R. Bedford Biochem. J. 1969 115 1047. 33 E. Hough and D. Rogers Biochem. Biophys. Res. Commun. 1974 57 73. 34 Y. Andres H. J. MacCordick and J. C. Hubert Biol. Met. 1991 4 207. 35 C. Ratledge and D. F. Ewing Biochem. J. 1978 175 853. 36 R. M. Hall and C. Ratledge J. Gen. Microbiol. 1984 130 1883. 37 R. M. Hall and C. Ratledge FEMS Microbiol. Lett. 1985 28 243. 38 S. Bosne and V. V. Levy-Febrault J. Clin. Microbiol. 1992 30 1225. 39 S. Chou P. Chedore and S. Kasatiya J. Clin. Microbiol. 1998 36 577. 40 V. J. Lévy-Fébrault K. S. Goh and H. L. David J. Clin. Microbiol. 1986 24 835.41 M. Daffé M. A. Lanéelle C. Asselineau V. Lévy-Fébrault and H. David Ann. Inst. Pasteur/Microbiol. 1983 134B 241. 42 M. Luquin V. Ausina F. L. Calahorra F. Belda M. G. Barcelo C. Celma and G. Prats J. Clin. Microbiol. 1991 29 120. 43 C. Q. F. Leite A. M. W. Barreto and S. R. A. Leite Rev. Microbiol. 1995 26 192. 44 J. Hu PhD Dissertation University of Notre Dame 1996. 45 D. St. C. Black and M. J. Wade Aust. J. Chem. 1972 25 1797. 46 P. J. Maurer and M. J. Miller J. Am. Chem. Soc. 1983 105 240. 47 J. Hu and M. J. Miller J. Am. Chem. Soc. 1997 119 3462. 48 S. Rogers and J. B. Neilands Biochemistry 1963 2 6. 49 G. C. Lancini E. Lazzari and A. Diena Farmaco Ed. Sci. 1969 24 169. 50 D. St. C. Black R. F. C. Brown and M. J. Wade Aust. J. Chem.1972 25 2155. 51 Y. Isowa and M. Ohmori Bull. Chem. Soc. Jpn. 1974 47 2672. 52 P. J. Maurer and M. J. Miller J. Am. Chem. Soc. 1982 104 3096. 53 J.-P. Genet S. Thorimbert and A.-M. Touzin Tetrahedron Lett. 1993 34 1159. 54 Y. Ohfune K. Hori and M. Sakaitini Tetrahedron Lett. 1986 27 6079. 55 D. St. C. Black R. F. C. Brown and M. J. Wade Aust. J. Chem. 1972 25 2429. 56 P. J. Maurer and M. J. Miller J. Org. Chem. 1981 46 2835. 57 J. Hu and M. J. Miller Tetrahedron Lett. 1995 36 6379. 58 J. Hu and M. J. Miller J. Org. Chem. 1994 59 4858. 59 Y. Xu and M. J. Miller J. Org. Chem. 1998 63 4314. 60 J. G. D. Carpenter and J. W. Moore J. Chem. Soc. (C) 1969 1610. 61 L. P. Macham and C. Ratledge J. Gen. Microbiol. 1975 89 379. 62 L. P. Macham M.C. Stephenson and C. Ratledge J. Gen. Microbiol. 1977 101 41. 63 L. P. Macham C. Ratledge and J. C. Nocton Infect. Immun. 1975 12 1242. 64 K. A. McCready and C. Ratledge Int. J. Syst. Bacteriol. 1977 27 288. 65 R. Barclay and C. Ratledge J. Bacteriol. 1983 153 1138. 66 A. J. M. Messenger R. M. Hall and C. Ratledge J. Gen. Microbiol. 1986 132 845. 67 R. Barclay and C. Ratledge J. Gen. Microbiol. 1988 134 771. 68 G. J. Sharman D. H. Williams D. F. Ewing and C. Ratledge Biochem. J. 1995 305 187. 69 G. J. Sharman D. H. Williams D. F. Ewing and C. Ratledge Chem. Biol. 1995 2 553. 70 S. J. Lane P. S. Marshall R. J. Upton C. Ratledge and M. Ewing Tetrahedron Lett. 1995 36 4129. 71 D. K. Wong J. Gobin M. A. Horwitz and B. W. Gibson J. Bacteriol.1996 178 6394. 72 S. J. Lane P. S. Marshall R. J. Upton and C. Ratledge BioMetals 1998 11 13. 73 C. Ratledge and M. Ewing Microbiology 1996 142 2207. 74 M. Allen A. J. Birch and A. R. Jones Aust. J. Chem. 1970 23 427. 75 J. E. Tateson Biochem. J. 1970 118 747. 76 A. T. Hudson and R. Bentley Tetrahedron Lett. 1970 11 2077. 77 A. T. Hudson and R. Bentley Biochemistry 1970 9 3984. 78 C. Ratledge and M. J. Hall FEBS Lett. 1970 10 309. 79 B. J. Marshall and C. Ratledge Biochem. Biophys. Acta 1972 264 106. 80 A. T. Hudson I. M. Campbell and R. Bentley Biochemistry 1970 9 3988. 81 S. T. Cole et al. Nature 1998 393 537. 82 L. E. N. Quadri J. Sello T. A. Keating P. H. Weinreb and C. T. Walsh Chem. Biol. 1998 5 631. 83 E. H. Fiss S. Yu and W.R. Jacobs Jr Mol. Microbiol. 1994 14 557. 84 S. Yu E. Fiss and W. R. Jacobs Jr. J. Bacteriol. 1998 180 4676. 85 W. Zhu J. E. L. Arceneaux M. L. Beggs B. R. Byers K. D. Eisenach and M. D. Lundrigan Mol. Microbiol. 1998 29 629. 86 O. Dussurget M. Rodriguez and I. Smith Mol. Microbiol. 1996 22 535. 87 C. Ratledge P. V. Patel and J. Mundy J. Gen. Microbiol. 1982 128 1559. 88 C. Ratledge Biochem. Biophys. Res. Commun. 1971 45 856. 89 C. Ratledge and B. J. Marshall Biochim. Biophys. Acta 1972 279 58. 90 L. Kato Int. J. Lepr. 1985 57 58. 91 R. S. Lambrecht and M. T. Collins Microb. Pathog. 1993 14 229. 92 C. Ratledge L. P. Macham K. A. Brown and B. J. Marshall Biochim. Biophys. Acta 1974 372 39. 115 Nat. Prod. Rep. 2000 17 99–116 93 A.J. M. Messenger and C. Ratledge J. Bacteriol. 1982 149 131. 94 J. Gobin and M. A. Horwitz J. Exp. Med. 1996 183 1527. 95 B. F. Matzanke R. Böhnke U. Möllmann R. Reissbrodt V. Schünemann and A. X. Trautwein BioMetals 1997 10 193. 96 B. Raghu G. R. Sarma and P. Venkatesan Med. Sci. Res. 1993 21 773. 97 M. C. Stephenson and C. Ratledge J. Gen. Microbiol. 1979 110 193. 98 M. C. Stephenson and C. Ratledge Biochem. Soc. Trans. 1978 6 423. 99 N. E. Morrison Int. J. Lepr. 1995 63 86. 100 M. C. Stephenson and C. Ratledge J. Gen. Microbiol. 1980 116 521. 101 R. M. Hall M. Sritharan A. J. M. Messenger and C. Ratledge J. Gen. Microbiol. 1987 133 2107. 102 M. Sritharan and C. Ratledge FEMS Microbiol. Lett. 1989 60 183. 103 L. G. Dover and C.Ratledge Microbiology 1996 142 1521. 104 M. Sritharan and C. Ratledge Biol. Met. 1990 2 203. 105 B. Raghu and G. R. Sarma Biochem. Mol. Biol. Int. 1993 31 333. 106 K. A. McCready and C. Ratledge J. Gen. Microbiol. 1979 113 67. 107 K. A. Brown and C. Ratledge FEBS Lett. 1975 53 262. 108 R. G. Deshpande M. B. Khan D. A. Bhat and R. G. Navalkar FEMS Immunol. Med. Microbiol. 1995 11 163. 109 M. C. V. Pessolani D. R. Smith B. Rivoire J. McCormick S. A. Hefta S. T. Cole and P. J. Brennan J. Exp. Med. 1994 180 319. 110 S. Kikuchi M. Fukumoto and H. Takahashi Biosci. Biotechnol. Biochem. 1994 58 885. 111 N. F. Inglis K. Stevenson A. H. F. Hosie and J. M. Sharp Gene 1994 150 205. 112 Iron and Infection eds. J. J. Bullen and E. Griffiths Wiley New York 1987.113 A. M. Rouhi Chem. Eng. News 1999 77 (20) 52 (May 17 1999). 114 A. Rattan A. Kalia and N. Ahmad Emerg. Infect. Dis. 1998 4 195. 115 D.E. Snider Jr. M. Raviglione and A. Kochi in Tuberculosis Pathogenesis Protection and Control ed. B. R. Bloom American Society of Microbiology Washington DC 1994 p. 3. 116 S. Lucas and A. M. Nelson in Tuberculosis Pathogenesis Protection and Control ed. B. R. Bloom American Society of Microbiologists Washington DC 1994 503. 117 C. A. Benson Curr. Opin. Infect. Dis. 1994 7 95. 118 G. S. Besra and D. Chatterjee in Tuberculosis Pathogenesis Protection and Control ed. B. R. Bloom American Society of Microbiologists Washington DC 1994 p. 285. 119 N. D. Connel and H. Nikaido in Tuberculosis Pathogenesis Protection and Control ed.B. R. Bloom American Society of Microbiologists Washington DC 1994 p. 333. 120 S. Bosne-David L. Bricard F. Ramiandrasoa A. DéRoussent G. Kunesh and A. Andremont Antimicrob. Agents Chemother. 1997 41 1837. 121 R. Barclay and C. Ratledge Zentralbl. Bakteriol. Mikrobiol. Hyg. Ser. A 1986 262 203. 122 K. A. Brown and C. Ratledge Biochim. Biophys. Acta 1975 385 207. 123 C. Ratledge and K. A. Brown Am. Rev. Resp. Dis. 1972 106 774. 124 K. Mdluli R. A. Slayden Y. Q. Zhu S. Ramaswamy X. Pan D. Mead D. D. Crane J. M. Musser and C. E. Barry Science 1998 280 1607. Nat. Prod. Rep. 2000 17 99–116 116 125 M. J. Miller and F. Malouin Acc. Chem. Res. 1993 26 241. 126 M. J. Miller F. Malouin E. K. Dolence C. M. Garsparski M. Ghosh P.R. Guzzo B. T. Lotz J. A. McKee A. Minnick and M. Teng in Recent Advances in the Chemistry of Anti-infective Agents ed. P. H. Bently and R. Ponsford R. Soc. Chem. Spec. Pub. 1993 119 135. 127 M. J. Miller and F. Malouin in The Development of Iron Chelators for Clinical Use eds. R. J. Bergeron and G. M. Brittenham CRC Boca Raton FL 1994 p. 275. 128 G. Benz T. Schroder J. Kurz C. Wunsche W. Karl G. Steffens J. Pfitzner and D. Schmidt Angew. Chem. Suppl. 1982 1322. 129 G. Benz L. Born M. Briedan R. Grosser J. Kurz H. Paulsen V. Sinnwell and B. Weber Leibigs Ann. Chem. 1984 1408. 130 G. Benz Leibigs Ann. Chem. 1984 1399. 131 G. Benz and D. Schmidt Liebigs Ann. Chem. 1984 1434. 132 H. Paulsen M. Briedan and G. Benz Liebigs Ann. Chem. 1987 565.133 H. J. Rogers in Iron Transport in Microbes Plants and Animals eds. G. Winkelmann D. van der Helm and J. B. Neilands VCH Weinheim FRG 1987 223. 134 J. B. Neilands and J. R. Valenta in Metal Ions in Biological Systems ed. H. Sigel Dekker New York 1985 vol. 19 p. 313 135 L. Vertesy W. Aretz H.-W. Fehlhaber and H. Kogler Helv. Chim. Acta 1995 78 46. 136 C. Walling Acc. Chem. Res. 1975 8 125. 137 J. L. Zweier J. Biol. Chem. 1988 263 1353. 138 E. Graf J. R. Mahoney R. G. Bryant and J. W. Eaton J. Biol. Chem. 1984 259 3620. 139 R. A. Floyd and C. A. Lewis Biochemistry 1983 22 2645. 140 J. M. C. Gutteridge R. Richmond and B. Halliwell Biochem. J. 1979 184 469. 141 L. D. Horwitz N. A. Sherman Y. Kong A. W. Pike J. Gobin P. V. Fennessey and M. A. Horwitz Proc. Natl. Acad. Sci. USA 1998 95 5263. 142 L. D. Horwitz M. A. Horwitz B. W. Gibson and J. Reeve US Patent 5 721 209 (Chem. Abstr. 1999 130 47472y). 143 Y. Kong E. J. Lesneefsky J. Ye and L. D. Horwitz Am. J. Physiol. 1994 267 H2371. 144 L. D. Horwitz US Patent 5 786 326 (Chem. Abstr. 1998 129 144856p). 145 R. M. Hall and C. Ratledge J. Gen. Microbiol. 1986 132 853. 146 C. Ratledge and P. V. Patel J. Gen. Microbiol. 1976 93 141. 147 C. Ratledge and G. A. Snow Biochem. J. 1974 139 407. 148 P. V. Patel and C. Ratledge Biochem. Soc. Trans. 1973 1 886. 149 Y. Murakami S. Kato M. Nakajima M. Matsuoka H. Kawai K. Shin-Ya and H. Seto J. Antibiot. 1996 49 839. 150 M. Tsukamoto K. Murooka S. Nakajima S. Abe H. Suzuki K. Hirano H. Kondo K. Kojira and H. Suda J. Antibiot. 1997 50 815. 151 K. Suenaga S. Kokubo C. Shinohara T. Tsuji and D. Uemura Tetrahedron Lett. 1999 40 1945. 152 L. D. Horwitz and K. B. Horwitz US Patent 5 837 677 (Cont.-in-part Chem. Abstr. 1999 130 47472y). 153 I. S. Towbridge and M. B. Omary Proc. Natl. Acad. Sci. USA 1981 78 3039. 154 T. Kameyama A. Takahashi S. Kurasawa M. Ishizuka Y. Okami T. Takeuchi and H. Umezawa J. Antibiot. 1987 40 1664. 155 R. J. Bergeron and J. S. McManis Tetrahedron 1989 45 4939. Review a809397k

ISSN:0265-0568    

DOI:10.1039/a809397k

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Recent progress in the chemistry of the Stemona alkaloids Ronaldo Aloise Pilli* and Maria da Conceição Ferreira de Oliveira Universidade Estadual de Campinas Instituto de Química Cx. Postal 6154 Campinas-SP CEP 13083-970 Brasil. E-mail pilli@iqm.unicamp.br Received (in Cambridge) 24th August 1999 Covering from 1975 to 1998 12 Introduction Structural classification 2.1 Stenine group 2.2 Stemoamide group 2.3 Tuberostemospironine group 2.4 Stemonamine group 2.5 Parvistemoline group 2.6 Miscellaneous group 3 Natural sources 3.1 Stemonaceae family 3.2 Phytochemical studies 45 Biological activities Synthetic sources 5.1 Stenine group 5.2 Stemoamide group 5.3 Tuberostemospironine group 678 Conclusion Acknowledgments References 1 Introduction This review focuses on the chemistry of the Stemona alkaloids and covers the literature from 1975 to 1998.In this period thirtyfive new Stemona alkaloids were isolated from Stemonaceae Ronaldo A. Pilli received his BSc degree in Chemistry from the Universidade Estadual de Campinas (Unicamp) Campinas SP (Brazil) in 1976 and in 1977 he joined the faculty staff at the same University as a teaching assistant. He carried out his PhD research at the same institution under the supervision of Professor Albert J. Kascheres working on the reactions of cyclopropenimines with nitrogen ylides (1977–81). In 1982 he joined Professor Clayton H. Heathcock group at the University of California Berkeley for postdoctoral work on the total synthesis of erythronolide A.In 1985 he started his independent research program at Unicamp aimed to develop and apply stereoselective methodologies to the total synthesis of natural products such as pheromones alkaloids and macrolides. Professor Pilli is the recipient of the 1989 Union Carbide Prize Brazil as the supervisor of the award winner project and of the 1999 Silver Jubilee Award of the Inter- Ronaldo A. Pilli This journal is © The Royal Society of Chemistry 2000 species and had their structures elucidated. More recently the total syntheses of some of these alkaloids were reported. The biological activity of some representatives has also been evaluated. The Stemona alkaloids represent a class of polycyclic alkaloids with relatively complex structures which emerged from the structural elucidation of its first representative tuberostemonine (2 Fig.2) in the sixties. The chemical investigation of Stemonaceae species was initially motivated by their use in Chinese and Japanese folk medicine in the treatment of respiratory diseases and as anthelmintics. However the biological activity of Stemonaceae species could not be associated with any of the Stemona alkaloids.1 The last review of this class of alkaloids covering the structural elucidation of tuberostemonine stenine oxotuberostemonine stemonine protostemonine stemofoline and tuberostemonine A was reported by Götz and Strunz in 1975.1 Additionally the physical data of eleven representatives of this family possessing unknown structures were included.Since then the isolation of new Stemona alkaloids and the elucidation of some previously unknown structures have been described in the literature.2–25 The total syntheses of some Stemona alkaloids have also been reported.26–35 More recently a review with five references concerning the synthetic studies on stenine was reported by Haruna et al.36 This review focuses on the structural classification isolation biological activity and total syntheses of this class of alkaloid. Special attention is paid to both structural classification and synthetic studies. national Foundation for Science Sweden. He has been a fellow of several national and international scientific organizations and is currently on the Editorial Board of Quimica Nova and Journal of the Brazilian Chemical Society.M. C. Ferreira de Oliveira was born in Fortaleza CE (Brazil) in 1967. She received her BSc degree from Universidade Regional de Blumenau (Blumenau SC) in 1992 and her MSc at Universidade Federal do Ceará (Fortaleza CE) in 1996. Her master degree involved the phytochemical study of Bredemeyera brevifolia (Polygalaceae). In 1996 she joined Professor Pilli’s group to develop her PhD work studying the stereochemical outcome of the addition of carbon nucleophiles to cyclic N-acyliminium ions and the application to the synthesis of Stemona alkaloids. M. C. Ferreira de Oliveira 117 Nat. Prod. Rep. 2000 17 117–127 2 Structural classification The Stemona alkaloids are structurally characterized by the presence of the pyrrolo[1,2-a]azepine nucleus,2 also named perhydroazaazulene3 and 4-azaazulene4 (A Fig.1). After the review by Götz and Strunz1 thirty-five new Stemona alkaloids were reported in the literature,2–25 currently comprising a total of forty-two structures. Fig. 1 Stemona alkaloid groups. Xu and coworkers have previously suggested that the Stemona alkaloids can be separated into eight structural groups according to the sites of connection between the basic ring and the side chain.4 However these authors have only specified the maistemonine,4 tuberostemonine,22 croomine22 and protostemonine23 groups. We have also classified these alkaloids according to their structural features into five groups (stenine I stemoamide II tuberostemospironine III stemonamine IV tuberostemoamide V (Fig.1)) containing the pyrrolo[1,2- a]azepine nucleus characteristic of the majority of the Stemona alkaloids and a miscellaneous group lacking this basic nucleus. The group denominations adopted in this review may differ from those previously suggested by Xu and coworkers4,22,23 since we decided to consider the name of the structurally simplest alkaloid of each group as the parent name. The name adopted for the basic skeleton in each group was based on the nomenclature of its members described in Chemical Abstracts. The numbering system of the structures was based on that described in the literature.3,4,11,12 2.1 Stenine group The stenine group currently comprises seven members stenine1 1 tuberostemonine1,3 2 tuberostemonine A1 3 tuberostemonol3 4 didehydrotuberostemonine3 5 bisdehydroneotuberostemonine22,25 6 and neotuberostemonine22,25 7 (Fig.2) which can be structurally represented by the tetracyclic furo[2,3-h]pyrrolo[3,2,1-jk][1]benzazepin-10(2H)-one nucleus (I Fig. 1). Didehydrotuberostemonine (5) has also been named bisdehydrotuberostemonine.22 Another stenine alkaloid named stemonine LG was reported in the literature17 but with only partial stereochemical assignment. Later on Dao and coworkers37 referring to this alkaloid as tuberostemonine LG established its structure by X-ray analysis which showed it to be identical to neotuberostemonine (7). The absolute configuration of stenine (1) was first established through its chemical conversion to derivatives of tuberostemonine (2) which had its Nat.Prod. Rep. 2000 17 117–127 118 Fig. 2 Stemona alkaloids of the stenine group (1–7) and oxotuberostemonine (8). absolute configuration revealed by X-ray diffraction analysis (heavy-atom method)1 and later by its asymmetric synthesis30,34 (see Section 5.1). The oxidative cleavage of the C-3–C- 18 bond in tuberostemonine A (3) afforded a lactam identical to the one obtained from tuberostemonine (2) thus revealing the absolute configuration depicted for tuberostemonine A (3) in Fig. 2.1 The relative configurations of tuberostemonol (4) and neotuberostemonine (7) were established by 2D-NMR studies. 3,22 The structure of didehydrotuberostemonine (5) was identified by direct comparison of physical and chemical data with those obtained from the oxidation products of tuberostemonine (2).3 Comparison of the 1H NMR chemical shifts of bisdehydroneotuberostemonine (6) and didehydrotuberostemonine (5) revealed for 6 the relative configuration represented in Fig.2 however the stereochemistry at C-10 was not depicted in ref. 22 but the ethyl group at C-10 was represented with b orientation in ref. 25. Except for stenine (1) the simplest representative alkaloid of this group all the other members have an a-methylg-butyrolactone ring attached to C-3 in the pyrrolidine ring A. Stenine (1) tuberostemonine (2) tuberostemonine A (3) tuberostemonol (4) and didehydrotuberostemonine (5) show cis relationships between H-11 H-12 and the methyl group at C- 13 in the lactone ring D.Bisdehydroneotuberostemonine (6) and neotuberostemonine (7) also display the cis relationship for these hydrogens which however are disposed trans to the methyl group at C-13. The absolute configuration at C-13 is the same as the one proposed for the other members of this group. Surprisingly tuberostemonine A (3) is the only Stemona alkaloid to display an (R)-absolute configuration at C-3 when the a-methyl-g-butyrolactone ring is attached to this stereogenic center. The cis B–C and C–D ring junction is observed for 1 2 3 and 7 while trans stereochemistry for the A–C ring junction is generally adopted except for neotuberostemonine (7). Tuberostemonol (4) is the only Stemona alkaloid to display a hydroxy group at C-9.Oxotuberostemonine1 8 possesses a structure closely related to the stenine group but with the oxygen atom of the lactone ring D reallocated from C-11 to C-1 keeping the same relative configuration. Additionally oxo-tuberostemonine (8) displays a hydroxy group at C-11 and it is the only Stemona alkaloid to display a double bond at C-9–C- 9a. Götz1 pointed out the possibility that oxotuberostemonine (8) is an artifact formed by air oxidation of tuberostemonine (2) since it has also been obtained from tuberostemonine oxidation with mercuric acetate. 2.2 Stemoamide group This group is currently represented by nine alkaloids stemoamide3 9 stemonine1,2,23 10 neostemonine23,2511 bisdehydroneostemonine23,25 12 protostemonine1,16,18,23 13 didehydroprotostemonine18,23,25 15 14 isoprotostemonine18,23,25 tuberostemoamide20,21 16 and stemoninine5,7,9 17 (Fig.3) Fig. 3 Stemona alkaloids of the stemoamide group and stemodiol (18). which display the tricyclic 2H-furo[3,2-c]pyrrolo[1,2-a]azepine nucleus (II Fig. 1). Additionally neostemodiol18 18 has been included in the stemoamide group despite lacking ring C since it can be associated to neostemonine (11) through dehydration to form ring C. Neostemodiol (18) has also been named stemodiol by the same authors.18 Some members of this group (10 11 12 13 14 and 15) have been reported as protostemonine-type alkaloids.23 Before the isolation of 11 the name neostemonine was applied to 12,18 but after that it has been changed to its current name bisdehydroneostemonine.23 Additionally 12 has been depicted in ref.25 with cis fused B and C rings. Alkaloid 9 has been mistakenly reported as stemonamide31 while structures 14 and 16 have also been reported as bisdehydroprotostemonine23,25 and stemoninoamide,20,21 respectively. Lin and coworkers reported different optical rotation values ([a]D +94 (c 0.06 MeOH)20 and [a]D 294 (c 0.06 MeOH)21) for 16. The alkaloid represented by structure 17 was also named stemoninoine20,21 and stemoninone.20 Stemoamide (9) had its relative configuration obtained by NMR studies and comparison of its 1H NMR chemical shifts and coupling constant values with those of stemoninine (17).3 Later on the absolute configuration of 9 was established through its asymmetric syntheses.29,33 Stemonine (10) had its absolute stereochemistry revealed by X-ray analysis of its hydrobromide hemihydrate by consideration of anomalous dispersion effects.38 Neostemonine (11) bisdehydroneostemonine (12) and tuberostemoamide (16) are represented by their relative configuration obtained from NMR studies and comparison of their 1H NMR data to those of 13 14 and 17 respectively.20,23 However the relative configuration at C-11 of 16 has not been specified.20 Protostemonine (13) and stemoninine (17) had their relative stereochemistries revealed from NMR studies9,18 while didehydroprotostemonine (14) had its relative configuration obtained after comparison of its NMR data to those of protostemonine (13).18,23 Additionally protostemonine (13) has been previously converted to its hydrate hydrochloride and than afforded stemonine (10) upon K2CO3 treatment or vacuum pyrolysis,1 and oxidation of 13 with Ag2O afforded 14.23 Comparison of the NMR data of isoprotostemonine (15) and protostemonine (13) revealed for the former alkaloid the relative configuration represented in Fig.3.18,23 The alkaloids 10 13 14 15 and 17 display an a-methyl-gbutyrolactone ring attached to C-3 in the pyrrolidine ring A. Moreover the trans ring fusion of the B–C rings the cis relationship between the hydrogens at C-9 and C-9a and the (S) absolute configuration at C-10 are noteworthy stereochemical features of this group of alkaloids. The Stemona alkaloids 11 12 13 14 and 15 have a disubstituted lactone ring attached to ring C at C-11 by a double bond as a distinct characteristic of this group.The Stemona alkaloids 16 and 17 display an unsaturated spirolactone ring fused at C-11. Interestingly these two alkaloids have an ethyl substituent at C-10 instead of the methyl substituent found in the other members of this group. Surprisingly isoprotostemonine (15) has the disubstituted lactone ring disposed with opposite geometry around the exocyclic double bond when compared to the other members of the group. In fact this is the only structural difference between protostemonine (13) and isoprotostemonine (15). 2.3 Tuberostemospironine group The tuberostemospironine group of Stemona alkaloids is characterized by a 2H-spiro[furan-2,9A[9H]pyrrolo[1,2-a]azepin]-5-one nucleus which displays a spiro g-lactone at C-9 of the basic ring (III Fig.1) and comprises seven members tuberostemospironine3 19 croomine6,19 20 stemospironine2 21 stemotinine8 22 isostemotinine8 23 stemonidine1,8 24 and didehydrocroomine19 25 (Fig. 4). The Stemona alkaloids 20 22 23 and 24 have been reported as croomine-type alkaloids.8,22 The relative configurations of alkaloids tuberostemospironine (19) stemotinine (22) isostemotinine (23) and stemonidine (24) were established by NMR studies3,8 while croomine6 (20) and stemospironine2 (21) had their absolute configurations obtained by X-ray analyses (heavy-atom method). The relative configuration of didehydrocroomine (25) was revealed by NMR studies and it was correlated with croomine (20) after Ag2O oxidation.19 Croomine (20) stemospironine (21) stemotinine 119 Nat.Prod. Rep. 2000 17 117–127 Fig. 4 Stemona alkaloids of the tuberostemospironine group. (22) and didehydrocroomine (25) display at C-9 an opposite stereochemistry to that found in tuberostemospironine (19) isostemotinine (23) and stemonidine (24). Of these seven alkaloids tuberostemospironine (19) is the only one which lacks the a-methyl-g-butyrolactone ring appended to C-3 of the pyrrolidine ring A. Curiously stemotinine (22) and isostemotinine (23) have an oxygen bridge between C-9a and C-6. In fact these two alkaloids are the only Stemona alkaloids with such a characteristic and they differ by the absolute configuration at C-9 and C-11.2.4 Stemonamine group Previously reported as the maistemonine group,4 this group is characterized by the tetracyclic 2AH,11H-spiro[1H-cyclopenta- [b]pyrrolo[1,2-a]azepine-11,2A-furan]-5A,10-dione nucleus with a spirolactone ring at C-12 (IV Fig. 1) which may be found in both absolute configurations. The stemonamine group includes the following Stemona alkaloids stemonamine4 26 isostemonamine4 27 stemonamide4,25 28 isostemonamide4,25 29 maistemonine4,13,16 30 and oxymaistemonine4,13,16 31 (Fig. 5). Fig. 5 Stemona alkaloids of the stemonamine group. The alkaloids 30 and 31 were first reported to display (R)- absolute configuration at C-9a.13,16 Later on their correct structures were revealed by conversion of 30 to 28.4 The literature24 also reports the name protostemotinine when Nat.Prod. Rep. 2000 17 117–127 120 referring to structure 30 despite the difference in the melting points reported for maistemonine4 (mp 205–207 °C) and protostemotinine24 (mp 214–246 °C). Curiously stemonamine (26) and isostemonamine (27) were identified as racemic alkaloids and stemonamine (26) displayed racemic pairs of molecules in the X-ray analysis.39 Stemonamide (28) and isostemonamide (29) had their relative configurations established by NMR studies.4 The relative configuration of oxymaistemonine (31) was obtained by comparison of its NMR data with those for maistemonine (30).13 The configuration at C-8 in 31 was confirmed by coupling constant value in combination with the inspection of the Dreiding structural model.13 Stemonamine (26) and stemonamide (28) only differ from isostemonamine (27) and isostemonamide (29) respectively by the absolute configuration at C-12.All the members of this group show the (S)-absolute configuration at C- 9a and the a-methyl-g-butyrolactone ring attached to C-3 is found only in the alkaloids maistemonine (30) and oxymaistemonine (31). 2.5 Parvistemoline group The parvistemoline alkaloids are characterized by the lack of the B–C ring fusion and a hexahydro-2,6-dimethyl-5-oxofuro[ 3,2-b]furan-3-yl moiety attached to C-9 in the pyrrolo [1,2-a]azepine nucleus (V Fig. 1). This group comprises the alkaloids parvistemoline11 32 parvistemonine10,15 33 and didehydroparvistemonine11 34 (Fig.6). Parvistemonine (33) Fig. 6 Stemona alkaloids of the parvistemoline group. and didehydroparvistemonine (34) have a g-lactone ring positioned at C-3. The structures of these alkaloids were established by IR MS and NMR studies but only parvistemonine (33) had its relative configuration unambigously depicted in the literature.10 2.6 Miscellaneous group The miscellaneous group includes eight Stemona alkaloids stemofoline1,2,12 35 oxystemofoline12 36 methoxystemofoline12 37 parvistemoninine15 38 parvistemoninol15 39 tuberostemonone3,14 40 tuberostemoninol20,21 41 and parvistemoamide11,15 42 (Fig. 7). The relative configurations at C-8 C-9a and C-10 of parvistemoamide (42) are not unambiguously depicted in ref.11 but the same group described in ref. 15 the relative stereochemistry shown in Fig. 7. Stemofoline (35) had its absolute configuration established by X-ray analysis of its hydrobromide monohydrate (heavy-atom method)40 while the alkaloids oxystemofoline12 (36) methoxystemofoline12 (37) and parvistemoamide11 (42) had their relative configurations obtained by 2D-NMR studies. Tuberostemonone14 (40) and tuberostemoninol20 (41) are represented by their relative configuration which were established by X-ray analyses. Fig. 7 Stemona alkaloids of the miscellaneous group. Although the members of this group lack the pyrrolo[1,2- a]azepine nucleus they still keep in their structure some characteristic fragments present in the members of the other groups.The alkaloids 35–37 and 38–39 are structurally the most complex Stemona alkaloids and differ from each other by the nature of the substituent attached to the side chain at C-3. The removal of the C-2–oxygen and C-8–oxygen bonds the C-3–C- 7 bond and the side chain at C-3 in 35–37 formally leads to the stemoamide alkaloid neostemonine (11) (Fig. 3). Tuberostemonone (40) can be associated with the stenine group as a product of their oxidative cleavage of the C-1–C-9a bond. Unlike the members of that group 40 shows a trans relationship between the C-5 and C-9 hydrogens and between the hydrogen at C-11 and the ethyl group at C-10. As for 40 tuberostemoninol (41) can also be associated with the stenine group by the oxidative cleavage of the C-1–C-9a bond (stenine group numbering) to form a dicarbonylic system followed by the nucleophilic attack of the enol form of the carbonyl group at C-9 to the carbonyl group at C-1.The structurally simplest Stemona alkaloid parvistemoamide (42) may be associated with the members of stemoamide group (Fig. 3) by the nucleophilic attack of the nitrogen atom of 42 to a keto group at C-9a followed by reduction at this carbon. 3 Natural sources 3.1 Stemonaceae family The family Stemonaceae (order Dioscoreales) is today the only source of the Stemona alkaloids. This family is a monocotyledon described by Engler in 1887.41 Although Dahlgren41 reported for this family the genera Stemona Croomia Stichoneuron and Pentastemona Duyfjes,42 and later Bouman,43 found evidence which allowed them to separate the genus Pentastemona into a new family Pentastemonaceae.Stemona earlier named Roxburghia is the most representative genus of the family Stemonaceae occurring from southern Asia and Malaysia to northern Australia. The literature reports the existence of 25 species for this genus. The genus Croomia comprises three species and occurs in Atlantic North America and Japan. The third genus Stichoneuron is composed of two species distributed in eastern Asia.41 3.2 Phytochemical studies Although the Stemonaceae family comprises more than 30 species the phytochemical investigation of this family is restricted to only eight of them most belonging to the genus Stemona (Table 1). As far as we know no phytochemical study Table 1 Stemona alkaloids isolated from Stemonaceae species Stemonaceae species S.tuberosa S. japonica S. parviflora S. sessilifolia S. mairei Stemona sp. C. japonica C. heterosepala Croomine 20 has been reported so far for the genus Stichoneuron. Ren-sheng Xu and coworkers initiated an extensive investigation of some Stemona alkaloid Stenine 1 1 Tuberostemonine 2 1 3 Tuberostemonol 4 3 Didehydrotuberostemonine 5 3 Bisdehydroneotuberostemonine 6 22 25 Neotuberostemonine 7 22 25 Oxotuberostemonine 8 1 Stemoamide 9 3 Tuberostemoamide (Stemoninoamide) 16 20 21 Tuberostemospironine 19 Stemotinine 22 Isostemotinine 23 Tuberostemonone 40 Tuberostemoninol 41 Stemonine 10 Neostemonine 11 Bisdehydroneostemonine 12 Protostemonine 13 Didehydroprotostemonine 14 Isoprotostemonine 15 Stemospironine 21 Stemonidine 24 Stemonamine 26 Isostemonamine 27 Stemonamide 28 Isostemonamide 29 Maistemonine (Protostemotinine) 30 Neostemodiol (Stemodiol) 18 Stemofoline 35 Parvistemoline 32 Parvistemonine 33 Didehydroparvistemonine 34 Stemofoline 35 Oxystemofoline 36 Methoxystemofoline 37 Parvistemoninine 38 Parvistemoninol 39 Parvistemoamide 42 Tuberostemonine 2 Tuberostemonine A 3 Stemoninine 17 Protostemotinine (Maistemonine) 30 Protostemonine 13 Maistemonine (Protostemotinine) 30 Oxymaistemonine 31 Protostemonine 13 Stemoninine 17 Croomine 20 Didehydrocroomine 25 Nat.Prod. Rep. 2000 17 117–127 Reference 3 8 8 3 14 20 21 1 23 23 25 18 23 25 1 18 23 18 23 25 18 23 25 2 1 4 4 4 25 4 25 4 18 18 1 2 11 10 15 11 12 12 15 12 15 15 11 15 1 1 9 24 16 13 16 13 16 1 5 7 19 19 6 121 Stemona species in the early 80’s leading to the isolation and structural elucidation of most of the currently known Stemona alkaloids.25 Most of the phytochemical studies of this family were restricted to the roots although studies of leaves,2 stems2 and rhizomes1,6,24 have also been reported.Due to their complex structures most of the Stemona alkaloids had their structure elucidated by crystallographic analyses.2,6,14,20,37–40 4 Biological activities The popular use of Stemonaceae extracts as insecticides vermifuges and in the treatment of respiratory diseases in China and Japan is described in the literature.1,2,23,44 The water extracts obtained from the roots of some Stemonaceae species were widely used in China against human and cattle parasites agricultural pests and as domestic insecticides.2 The basic methanolic extracts obtained from fresh leaves of Stemona japonica showed strong insecticidal activity against silk worm larvae.2 The crude extracts of Stemonaceae species have also shown antitubercular and antitussive activities.44 These biological activities motivated the chemical investigation of Stemonaceae species in order to find their active principles.Tuberostemonine (2) (Fig. 2) was the first Stemona alkaloid to have its biological activity tested.Although the initial results did not show activity against Hymenolepis nana and Nematospiroides dubius,1 its anthelminthic activity was detected when tested against Angiostrongylus cantonensis Dipylidium caninum and Fasciola hepatica with an effect on the motility of these helminthic worms. These results motivated Shinozaki and Ishida to test the action of this alkaloid on the neuromuscular transmission in crayfish which is considered a model for studying the mechanism of drug action in the mammalian central nervous system. The results obtained in the tests demonstrated that tuberostemonine depressed glutamate-induced responses at similar concentrations to those of established glutamate inhibitors.44 The insecticidal activity of stemonine (10) (Fig.3) stemospironine (21) (Fig. 4) and stemofoline (35) (Fig. 7) against the fourth instar Bombyx mori (silkworm larvae) is reported in the literature.2 Alkaloid 35 showed a very potent activity against the larvae being 104 times more toxic than alkaloid 21. Stemonine (10) and stemospironine (21) showed similar moderate results. Otherwise these three alkaloids showed no activity against the fifth instar larvae of cabbage army worm (Mamestra brassicae). Neostemonine (11) and Scheme 1 Reagents (a) Et2AlCl CHCl3 80 °C (67%); (b) H2NNH2 H2O MeOH reflux (87%); (c) MeI K2CO3 MeOH reflux (100%); (d) AcCl 0 °C ? rt (100%); (e) mesitylene reflux; then MeOH reflux (94%); (f) 9-BBN THF 0 °C ? rt; then NaBO3·4H2O H2O rt (95%); (g) MsCl Et3N CH2Cl2 0 °C ?rt (100%); (h) MeLi THF 278 °C ?rt (83%); (i) Jones’ reagent acetone 0 °C (83%); (j) I2 THF–Et2O aq.NaHCO3 0 °C ?rt (95%); (k) DBU toluene reflux (98%); (l) 2-methylpropan-2-ol MeOH NaBH4 50 °C (100%); (m) TBSCl Et3N CH2Cl2 DMAP rt (97%); (n) MeC(OMe)2NMe2 xylenes reflux (93%); (o) I2 THF H2O rt (75%); (p) CH2CHCH2SnBu3 AIBN C6H6 reflux (83%); (q) LDA MeI THF HMPA 278 °C (87%); (r) DMSO (COCl)2 CH2Cl2; 278 °C then Et3N (99%); (s) Ph3PNCHCO2Et CHCl3 reflux (91%); (t) Red-Al CuBr THF butan-2-ol 278 °C ?220 °C (85%); (u) Me3SiI CHCl3 rt (94%); (v) mesitylene reflux (91%); (w) OsO4 (cat.) NaIO4 THF H2O rt (84%); (x) HSCH2CH2SH SiO2–SOCl2 CH2Cl2 rt (100%); (y) (p-MeOC6H4PS2)2 CH2Cl2 rt (100%); (z) W-2 Raney-Ni EtOH reflux (80%).Nat. Prod. Rep. 2000 17 117–127 122 isoprotostemonine (15) (Fig. 3) had their antifeeding activity tested against last-instar larvae of Spodoptera litura but with little activity.23 No antimicrobial or antiviral activities were detected for these two alkaloids.23 As far as we know no other Stemona alkaloid has had its biological activity tested. 5 Synthetic sources The complex molecular architecture of the Stemona alkaloids has stimulated the synthetic work on this family of natural products. In this section only the approaches which culminated in the total synthesis of a member of this family will be discussed although several studies have also appeared directed towards the assembly of their major structural motifs.45–53 5.1 Stenine group Stenine (1) is the only representative of this group of Stemona alkaloids which has so far yielded to total synthesis.Chen and Hart first described the total synthesis of racemic stenine (1) in 1990.27,28 The construction of the advanced intermediate 50 containing the ACD substructure was initiated with an intramolecular Diels–Alder reaction (43 ? 44 Scheme 1) followed by a Curtius rearrangement (45 ? 46) which set the stage for ring A formation (Scheme 1). Claisen–Eschenmoser rearrangement (48 ? 49) and iodolactonization completed the assembly of tricyclic intermediate 50. Ring B was finally put in place after homologation of the side chain at C-9 and intramolecular lactam formation (50 ?51). The first total synthesis of racemic stenine (1) was completed in 25 steps from 43 and 7.2% overall yield after the conversion of the allylic residue at C-10 to the requisite ethyl substituent and the adjustment of the oxidation level at ring B.Wipf and coworkers30 have reported the first asymmetric synthesis of (2)-stenine (1) based on an efficient preparation of a hydroindolenone intermediate through the oxidation of Nbenzyloxycarbonyltyrosine with hypervalent iodine followed by the reduction of the corresponding p-allylpalladium intermediate (52 ? 54 Scheme 2). The stereogenic center at C-9 was established through enolate alkylation and the acetamido side chain at C-12 by a Claisen–Eschenmoser rearrangement (54 ? 55). Selective cleavage of the terminal olefin was accomplished with Sharpless asymmetric dihydroxylation fol-lowed by sodium periodate cleavage of the corresponding diol.Reductive decarboxylation (56 ? 57) set the stage for iodolactonization followed by a stereoselective radical allyla- 2 MeOH NaHCO3 23 °C (54%); (b) Bz2O CH2Cl2 pyridine DMAP reflux (90%); (c) NaBH4 CeCl3·7H2O MeOH 2(dba)3·CHCl3 THF nBu3P HCO2H Et3N 60 °C (68%); (e) TPAP (cat.) NMO CH2Cl2 MS 4 Å 0 °C ? rt (90%); (f) KHMDS 2CH(CH2)3OTf THF 260 °C (51%); (g) NaBH4 CeCl3·7H2O THF MeOH 40 °C (91%); (h) MeC(OMe)2NMe2 xylenes reflux 2O 5 °C; then tert-BuOH H2O NaIO4 rt (82%); (j) NaBH4 THF MeOH (93%); (k) TIPSCl imidazole 4-DMAP (cat.) 2Cl2 rt (100%); (l) LiOH THF MeOH H2O 40 °C (90%); (m) PhOP(O)Cl2 C6H5SeH Et3N THF 0 °C ?22 °C; (n) nBu3SnH AIBN (cat.) xylenes 2 THF pH 5.5 21 °C (85%); (p) CH2CHCH2SnBu3 AIBN (cat.) 80 °C (90%); (q) LDA THF HMPA MeI 278 °C (87%); 4 (cat.) NaIO4 THF H2O tert-BuOH 0 °C ? 21 °C; (s) NaBH4 THF MeOH 240 °C (63% 2 steps); (t) o-(NO2)PhSeCN nBu3P THF 0 °C; 2O2 THF 21 °C (87%); (u) HF CH3CN 0 °C; (v) Dess–Martin periodinane CH2Cl2 21 °C; then THF 2-methylbut-2-ene NaClO2 aq.Na2HPO4 2 Pd(OH)2/C MeOH 21 °C; (x) C6F5P(O)Ph2 CH2Cl2 21 °C (71% 4 steps); (y) (p-MeOC6H4PS2)2 CH2Cl2 21 °C (93%); (z) Raney-Ni EtOH Scheme 2 Reagents (a) PhI(OAc) THF rt (99%); (d) Pd toluene 280 °C; then CH (85%); (i) AD-mix-b tert-BuOH H CH 130 °C (79% 2 steps); (o) I (r) OsO then H 0 °C; (w) H 21 °C (78%). Scheme 3 Reagents (a) nBuLi THF 225 °C; then (E,E)-MPMO(CH2)4CHNCH–CHNCH–CH2Cl HMPA 278 °C ?rt; (b) pTsOH H2O MeOH THF rt (68% 2 steps); (c) pyr·SO3 DMSO Et3N CH2Cl2 0 °C ? rt (85%); (d) A Et3N LiCl THF 0 °C ? rt (90%); (e) Me2AlCl CH2Cl2 220 °C (85%); (f) AgNO3 N-chlorosuccinimide CH3CN–H2O 0 °C (80%); (g) LiSEt THF 0 °C (91%); (h) Et3SiH 10% Pd/C acetone 0 °C ? rt (100%); (i) NaClO2 NaH2PO4 2-methylbut-2-ene tert-BuOH H2O 0 °C ? rt (100%); (j) (PhO)2P(O)N3 DMF Et3N 60 °C; (k) MeOH CuCl (cat.) rt (82% 2 steps); (l) TMSCl NaI CH3CN Et3N 50 °C; (m) MCPBA hexane CH2Cl2 215 °C ? rt; (n) H5IO6 THF H2O rt; then I2 NaHCO3 rt (50% 3 steps); (o) CSA CH(OMe)3 MeOH CH2Cl2 rt (90%); (p) CH2NCHCH2SnBu3 AIBN (cat.) toluene 80 °C (80%); (q) LDA THF HMPA 278 °C; then MeI 278 °C (73%); (r) Et3SiH BF3·OEt2 CH3CN 0 °C (82%); (s) OsO4 (cat.) NaIO4 THF H2O rt (75%); (t) HSCH2CH2SH BF3·OEt2 CH2Cl2 215 °C (81%); (u) W2-Raney-Ni EtOH reflux (85%); (v) MsCl Et3N CH2Cl2 0 °C (88%); (w) NaI acetone reflux (98%); (x) TMSI CH2Cl2 rt; (y) CH3CN reflux (70% 2 steps).tion (57 ? 58) and enolate alkylation a sequence of events which resembles the approach by Chen and Hart.27,28 The azepine ring B was formed through intramolecular nitrogen 123 Nat. Prod. Rep. 2000 17 117–127 acylation and the total synthesis was completed by the reduction of lactam 60 to afford (2)-1 in 26 steps from Cbz-tyrosine (52) and ca. 1.0% yield. An asymmetric intramolecular Diels–Alder reaction was employed by Morimoto and coworkers34 to construct the bicyclic ketone 63 with four stereogenic centers correctly assembled for the synthesis of (2)-1 and which was later on converted to the tricyclic key intermediate 66 containing the ACD rings after a modified Curtius rearrangement (64 ? 65 Scheme 3) iodolactonization (65 ? 66) radical allylation and methylation at C-11 (66 ? 67).The synthesis of (2)-1 was completed in 24 steps from dithiane 61 and ca. 2% overall yield after construction of ring B through an intramolecular nitrogen alkylation (68 ? 1). 5.2 Stemoamide group The tricyclic alkaloid stemoamide (9) is a typical representative of this group of Stemona alkaloids and it has been synthesized several times over the last few years including some very efficient approaches. Williams and coworkers29 succeeded in preparing (2)-stemoamide (9) starting from commercially available methyl (R)-3-hydroxy-2-methylpropionate which was homologated and coupled with (S)-4-benzyloxazolidin-2-one to afford chiral imide 69 (7 steps and 85% overall yield).An asymmetric boron aldol reaction with 4-benzyloxybutanal installed the stereogenic centers at C-8 and C-9 (70 Scheme 4). The correct stereochemistry at C-9a was established after chain elongation reduction with lithium triethylborohydride (exclusively from the carbonyl si face) mesylation (70 ? 71) and methanesulfonate displacement with sodium azide which proceeded with inversion of configuration (71 ? 72). At this point all the carbons and the stereogenic centers of (2)-stemoamide (9) were in place and the remaining steps were dedicated to the formation of rings A B and C and functional group interconversions (Scheme 4).The first total synthesis of (2)-stemoamide was then completed in 25 steps from (R)- methyl-3-hydroxy-2-methylpropionate and 5.6% overall yield. Kohno and Narasaka31 devised a short synthesis of (±)-stemoamide (9) mistakenly designated as (±)-stemonamide by these authors by applying the oxidative coupling reaction of 2-tributylstannyl-N-Boc-pyrrolidine with silyl enol ethers. The key intermediate 77 was produced in 65% yield as a mixture of stereoisomers which led to a separable mixture of diastereoisomers (78a+78b = 4+1) upon hydrogenation of the acetylenic bond. The formation of 77 is rationalized through the addition of silyl enol ether 76 (E+Z = 1+1) to an intermediate Nacyliminium ion derived from N-Boc-2-tributylstannylpyrrolidine (Scheme 5).The stereogenic center at C-8 was established after NaBH4 reduction of 78a which afforded g-lactone 79 in 59% yield. The alcohol with the wrong stereochemistry at C-8 was also obtained in 25% yield and it was converted to 79 through a 3-step sequence. In the final steps of the synthesis ring B was formed by intramolecular nitrogen alkylation and the correct stereochemistry at C-10 was established by stereoselective methylation of the lithium enolate of the g-lactone. This concise approach required 12 steps from 5-benzyloxypent- 3-yn-2-one and provided (±)-stemoamide (9) in ca. 2% overall yield. A concise and efficient approach to (2)-stemoamide (9) based on an intramolecular enyne metathesis was developed by Kinoshita and Mori.33 Starting from lactam 81 prepared from (2)-pyroglutamic acid the acetylene 82 was obtained in 5 steps and 50% overall yield (Scheme 6).The construction of ring B was efficiently accomplished by enyne metathesis (87% yield) using catalytic amount of Grubb’s catalyst (82 ? 83 Scheme 6). Reduction to the saturated ester followed by bromolactonization of the mixture of epimeric carboxylic acids afforded unsaturated lactone 85 (31% yield) and the corresponding bromolactone 84 (21% yield) which could be Nat. Prod. Rep. 2000 17 117–127 124 Scheme 4 Reagents (a) n-Bu2BOTf CH2Cl2 Et3N 278 °C ? 0 °C; then 4-benzyloxybutanal 278 °C ? 0 °C (88%); (b) aq. HF CH3CN rt; sat. aq. NaHCO3 K2CO3 (82%); (c) TBDMSOTf collidine CH2Cl2 278 °C ? rt (97%); (d) 4-iodobut-1-ene tert-BuLi Et2O 2100 °C; then TBDMSOTf collidine 278 °C ?rt (78%); (e) LiEt3BH THF 278 °C ? rt (91%); (f) MsCl pyridine rt (96%); (g) NaN3 HMPA rt; (h) O3 CH2Cl2 MeOH 278 °C; then Me2S 278 °C ? rt (49% 2 steps); (i) NaClO2 NaH2PO4•H2O CH3CN tert-BuOH H2O 2-methylbut-2-ene 0 °C; (j) CH2N2 Et2O 0 °C (96% 2 steps); (k) PPh3 THF H2O reflux (87%); (l) H2 10% Pd/C EtOH; (m) MsCl pyridine rt; (n) NaH THF rt (71% 3 steps); (o) HF·Et3N CH3CN rt (63%); (p) Dess–Martin periodinane pyridine CH2Cl2 rt; (q) TBAF THF rt (94% 2 steps); (r) PDC CH2Cl2 reflux (80%).converted to 85 (50% yield) by treatment with Et3N. The correct stereochemistry at C-10 was established by reduction of 85 with NaBH4 in the presence of NiCl2•6H2O in methanol to give (2)-stemoamide (9) in 14 steps from (2)-pyroglutamic acid and 9% overall yield.By far the most concise and efficient approach to (±)-stemoamide (9) was developed by Jacobi and Lee35 and featured an intramolecular Diels–Alder–retro Diels–Alder cycloaddition between the 2-methoxyoxazole and acetylenic moieties in 89 followed by hydrolysis to set the correct relative configuration at C-8 and C-9a (89 ? 90 Scheme 7). The stereochemistry at C-9 and C-10 was established after nickel boride reduction of the unsaturated butyrolactone ring and epimerization at C-10 to afford (±)-stemoamide (9) in 73% yield together with its epimer at C-9 and C-10. Overall the total synthesis of (±)-stemoamide (9) was achieved in 7 steps from 4-chlorobutyryl chloride (86) and 20% overall yield.5.3 Tuberostemospironine group (+)-Croomine (20) a prototypical example of the tuberostemospironine group was the first Stemona alkaloid to yield to total synthesis. In 1989 Williams and coworkers26 disclosed its total synthesis featuring an intermolecular Staudinger reaction followed by an iodoamination step to construct the Scheme 5 Reagents (a) TBSCl Et3N NaI CH3CN 50 °C (92%); (b) tert-butyl-2-(tributylstannyl)acetate TBACN EtCN K2CO3 MS 4 Å 0 °C (85%); (c) TBSCl Et3N NaI CH3CN 50 °C (60%); (d) 1-(tertbutoxycarbonyl)-2-(tributylstannyl)pyrrolidine CAN MS 4 Å EtCN 245 °C (65%); (e) H2 10% Pd/C MeOH rt (90% 78a 78b = 4:1); (f) NaBH4 THF MeOH rt (59%); (g) 10% Pd/C MeOH HCO2H rt (89%); (h) MsCl Et3N CH2Cl2 rt (96%); (i) RuO2 (cat.) NaIO4 AcOEt H2O rt (60%); (j) 1 M HCl–AcOEt rt (89%); (k) NaH THF rt (62%); (l) LDA THF 278 °C; then MeI 278 °C ? rt (59%).Scheme 6 Reagents (a) NaH DMF 5-bromopent-1-ene (89%); (b) TsOH MeOH (91%); (c) (COCl)2 DMSO Et3N; (d) CBr4 Ph3P (87% 2 steps); (e) n-BuLi THF 298 °C (72%); (f) LDA HMPA THF ClCO2Me 298 °C (68%); (g) Cl2Ru[P(C6H11)3]2CHPh CH2Cl2 rt (87%); (h) NaBH4 MeOH (85%); (i) NaOH MeOH H2O; (j) CuBr2 on Al2O3 (84 25% and 85 31%); (k) Et3N rt (50%); (l) NaBH4 NiCl2•6H2O MeOH (76%). pyrrolo[1,2-a]azepine nucleus and the g-butyrolactone ring attached at C-3 (Scheme 8). As in the total synthesis of (2)-stemoamide by the same group,29 Williams and coworkers started with methyl (S)-2-methyl-3-hydroxypropionate which was converted to acetylene 91 after 4 steps and 72% overall yield.Sharpless asymmetric epoxidation of (E)-trisubstituted allylic alcohol 93 and a two-carbon homologation of the corresponding aldehyde provided epoxide 94 which set the stage for the regioselective epoxide opening with lithium azide (94 ? 95 Scheme 8). Chain homologation (95 ? 96) and glactone formation (96 ?97) was followed by ring B formation Scheme 7 Reagents (a) CH (80%); (b) succinimide (97%); (c) NaBH (e) CH (g) NaBH 3CH(NH2)CO2Me C5H5N; then P2O5 4; (d) MeOH H+ (72% 2 steps); 3C·CSnBu3 BF3·OEt2 (92%); (f) diethylbenzene reflux (50–55%); 4 NiCl2 MeOH 230 °C (73%). through an intramolecular Staudinger reaction (97 ?98). Rings A and D were formed in a single step by iodoamination of bicyclic intermediate 98 an impressive transformation which also set the correct stereochemistry at C-3 and C-14 and yielded (+)-croomine (20) in 25% yield from 98 which was recovered in 50–60% yield.The first total synthesis of (+)-croomine (20) was carried out in 26 steps and about 0.5% overall yield from methyl (S)-2-methyl-3-hydroxypropionate. A shorter and more efficient route to (+)-croomine (20) was devised by Martin and Barr32 who employed the vinylogous Mannich addition of 2-silyloxyfuran 100 to a chiral Nacyliminium ion derived from (S)-pyroglutamic acid to connect rings A and C and to set the correct stereochemistries at C-9 and C-9a (100 ?101 Scheme 9). The stereochemistry at C-11 was set after hydrogenation of the double bond in ring C (101 ? 102) probably directed by the basic nitrogen of the pyrrolidine ring and ring B was put in place through an intramolecular nitrogen alkylation (102 ? 103).The thermally unstable acid chloride from intermediate 103 gave rise to the corresponding iminium ion which was trapped with 2-triisopropylsilyloxy- 3-methylfuran. This second vinylogous Mannich transformation (103 ?104) afforded a 47% combined yield of the desired isomer 104 and its C-14 epimer (2+1 ratio). The desired adduct 104 was submitted to a stereoselective hydrogenation to afford (+)-croomine (20) in 9 steps and approximately 5% overall yield from 3-methylfuran-2(5H)-one. 6 Conclusion Since the publication of the last review on the chemistry of the Stemona alkaloids in 1975 the body of information about this family of alkaloids has grown steadily.From a few representatives with defined structure (stenine (1) tuberostemonine (2) tuberostemonine A (3) oxotuberostemonine (8) stemonine (10) protostemonine (13) and stemofoline (35)) known at that time 35 new representatives were isolated and had their structures elucidated. Croomine (20) stemospironine (21) stemonamine (26) isostemonamine (27) tuberostemonone (39) and tuberostemoninol (40) had their structures established by X-ray analyses which also provided the absolute configuration for croomine (20) and stemospironine (21). Interestingly stemonamine (26) and isostemonamine (27) were isolated in racemic form. For the other alkaloids of this family isolated in the period covered in this review structural evidence was provided mainly by NMR studies.125 Nat. Prod. Rep. 2000 17 117–127 Scheme 8 Reagents (a) nBuLi THF 278 °C ? 0 °C; then ClCO2Me 278 °C (63%); (b) BnO(CH2)4MgBr DMS CuBr TMEDA Et2O 278 °C (95%); (c) DIBAL-H CH2Cl2 278 °C (98%); (d) Ti(OiPr)4 (cat.) D-DIPT (cat.) tert-BuOOH MS 4 Å CH2Cl2 250 °C (83%); (e) (COCl)2 DMSO CH2Cl2 Et3N 278 °C ? 0 °C; (f) Ph3PNCHCO2Me 0 °C ? rt (89% 2 steps); (g) LiBH4 Et2O MeOH 0 °C (81%); (h) 5% Rh/Al2O3 H2 THF (62%); (i) BzCl Et3N CH2Cl2 0 °C ? rt (97%); (j) LiN3 DMPU 110 °C (94%); (k) BF3·OEt2 CH2Cl2 0 °C (81%); (l) LiOH THF aq. THF MeOH H MeOH (97%); (m) (COCl)2 DMSO CH2Cl2 Et3N 278 °C ?0 °C (91%); (n) A THF 210 °C (70–81%); (o) aq.HBF4 MeOH (72%); (p) LiOH 2O 22 °C (86%); (q) Jones’ reagent THF 0 °C; (r) CH2N2 Et2O (78% 2 steps); (s) BCl3 CH2Cl2 278 °C ? 0 °C; then MeOH 278 °C (77%); (t) (COCl)2 DMSO CH2Cl2 Et3N 278 °C ?0 °C (92%); (u) Ph3P THF 22 °C; then NaBH4 MeOH (90%); (v) I2 CH2Cl2 Et2O 22 °C (25%). Noteworthy are the total syntheses of stenine (1) stemoamide (9) and croomine (20) carried out by several groups which definitively established the absolute configuration of these three alkaloids. Considering that the Stemonaceae family comprises more than 30 species and currently phytochemical investigation is restricted to only 8 of them the isolation of other Stemona alkaloids can be expected in the future as well as continuing progress towards the total syntheses of other representatives.7 Acknowledgements The authors wish to acknowledge the financial support from Fapesp (scholarship to MCFO) and CNPq (scholarship to RAP). We are also indebted to Professor Bai Dong-Lu (Shangai Institute of Materia Medica Shangai China) for providing references 7 10–13 and 18–20 and Professor Maria do Carmo Nat. Prod. Rep. 2000 17 117–127 126 Scheme 9 Reagents (a) s-BuLi TMEDA THF 0 °C; then BrCH2(CH2)2CH2Br (83%); (b) A 5% TIPSOTf CH2Cl2 0 °C (32%); (c) CF3CO2H CH2Cl2 rt; (d) 3% Rh/C H2 EtOAc EtOH ( > 96% 2 steps); (e) N-methylmorpholine DMF reflux; (f) 3 M aq. HBr 60 °C (74% 2 steps); (g) POCl3 DMF rt; then 99 (ca. 32%); (h) 10% Pd/C H2 10% HCl– EtOAc (85%). Estanislau do Amaral (Instituto de Biologia Unicamp Brazil) for helpful discussions on the botanical classification of the Stemonaceae family.8 References 1 M. Götz and G. M. Strunz ‘Tuberostemonine and Related Compounds The Chemistry of Stemona Alkaloids’ in Alkaloids vol. 9 ed. G. Wiesner MTP International Review of Sciences Organic Chemistry Series One Butterworths London 1975 pp. 143–160. 2 K. Sakata K. Aoki C.-F. Chang A. Sakurai S. Tamura and S. Murakoshi Agric. Biol. Chem. 1978 42 457. 3 W.-H. Lin Y. Ye and R.-S. Xu J. Nat. Prod. 1992 55 571. 4 Y. Ye G.-W. Qin and R.-S. Xu J. Nat. Prod. 1994 57 665. 5 C. Kuo and T.-T. Chu Chem. Abstr. 1979 90 164717y. 6 T. Noro S. Fukushima A. Ueno T. Miyase Y. Iitaka and Y. Saiki Chem. Pharm. Bull. 1979 27 1495. 7 G. Jia Acta Chim.Sinica 1981 39 865. 8 R.-S. Xu Y.-J. Lu J.-H. Chu T. Iwashita H. Naoki Y. Naya and K. 9 D. Cheng J. Guo T. T. Chu and E. Roder J. Nat. Prod. 1988 51 10 W.-H. Lin B.-P. Yin Z.-J. Tang R.-S. Xu and Q.-X. Zhong Acta Chim. 11 W.-H. Lin R.-S. Xu and Q.-X. Zhong Acta Chim. Sinica 1991 49 12 W.-H. Lin R.-S. Xu and Q.-X. Zhong Acta Chim. Sinica 1991 49 Nakanishi Tetrahedron 1982 38 2667. 202. Sinica 1990 48 811. 927. 1034. 13 W. H. Lin Y. Ye and R. S. Xu Chin. Chem. Lett. 1991 2 369. 14 W.-H. Lin R.-S. Xu R.-J. Wang and T. C. W. Mak J. Crystallogr. Spec. Res. 1991 21 189. 15 R.-S. Xu Z.-J. Tang S.-C. Feng Y.-P. Yang W.-H. Lin Q.-X. Zhong and Y. Zhong Mem. Inst. Oswaldo Cruz 1991 86 55. 16 W. Lin Y. Ye and R. Xu Chem. Abstr. 1992 116 148183w. 17 P.T. Ky V. N. Kim and N. X. Dung Chem. Abstr. 1992 117 108076c. 18 Y. Ye and R. S. Xu Chin. Chem. Lett. 1992 3 511. 19 W. H. Lin M. S. Cai B. P. Ying and R. Feng Acta Pharm. Sinica 1993 20 W. H. Lin L. Wang L. Qiao and M. S. Cai Chin. Chem. Lett. 1993 4 21 W. H. Lin L. Ma M. S. Cai and R. A. Barnes Phytochemistry 1994 28 202. 1067. 36 1333. 22 Y. Ye G.-W. Qin and R.-S. Xu Phytochemistry 1994 37 1201. 23 Y. Ye G.-W. Qin and R.-S. Xu Phytochemistry 1994 37 1205. 24 X. Cong H. Zhao D. Guillaume G. Xu Y. Lu and Q. Zheng Phytochemistry 1995 40 615. 25 G.-W. Qin and R.-S. Xu Med. Res. Rev. 1998 18 375. 26 D. R. Williams D. L. Brown and J. W. Benbow J. Am. Chem. Soc. 1989 111 1923. 27 C. Chen and D. J. Hart J. Org. Chem. 1990 55 6236. 28 C.-Y.Chen and D. J. Hart J. Org. Chem. 1993 58 3840. 29 D. R. Williams J. P. Reddy and G. S. Amato Tetrahedron Lett. 1994 35 6417. 30 P. Wipf Y. Kim and D. M. Goldstein J. Am. Chem. Soc. 1995 117 11106. 31 Y. Kohno and K. Narasaka Bull. Chem. Soc. Jpn. 1996 69 2063. 32 S. F. Martin and K. J. Barr J. Am. Chem. Soc. 1996 118 3299. 33 (a) A. Kinoshita and M. Mori J. Org. Chem. 1996 61 8356; (b) A. Kinoshita and M. Mori Heterocycles 1997 46 287. 34 Y. Morimoto M. Iwahashi K. Nishida Y. Hayashi and H. Shirahama Angew. Chem. Int. Ed. Engl. 1996 35 904. 35 P. A. Jacobi and K. Lee J. Am. Chem. Soc. 1997 119 3409. 36 M. Haruna T. Kobayashi and K. Ito Chem. Abstr. 1985 105 R79195k. 37 C. N. Dao P. Luger P. T. Ky V. N. Kim and N. X. Dung Acta Crystallogr.Sect. C 1994 50 1612. 38 H. Koyama and K. Oda J. Chem. Soc. (B) 1970 1330. 39 H. Iizuka H. Irie N. Masaki K. Osaki and S. Uyeo J. Chem. Soc. Chem. Commun. 1973 125. 40 H. Irie N. N. Masaki K. Ohno K. Osaki T. Taga and S. Uyeo Chem. Commun. 1970 1066. 41 R. M. T. Dahlgren H. T. Clifford and P. F. Yeo The Families of The Monocotyledons. Structure Evolution and Taxonomy Springer-Verlag Berlin 1985. 42 B. E. E. Duyfjes Blumea 1991 36 239. 43 F. Bouman and N. Devente Blumea 1992 36 501. 44 H. Shinozaki and M. Ishida Brain Res. 1985 334 33. 45 L. Xiang and A. P. Kozikowski Synlett 1990 279. 46 R. L. Beddoes M. P. H. Davies and E. J. Thomas J. Chem. Soc. Chem. Commun. 1992 538. 47 P. Wipf and Y. Kim Tetrahedron Lett. 1992 33 5477. 48 Y. Morimoto K. Nishida Y. Hayashi and H. Shirahama Tetrahedron Lett. 1993 34 5773. 49 S. Martin J. Heterocycl. Chem. 1994 31 679. 50 Y. Morimoto and M. Iwahashi Synlett 1995 1221. 51 D. M. Goldstein and P. Wipf Tetrahedron Lett. 1996 37 739. 52 J. H. Rigby S. Laurent A. Cavezza and M. J. Heeg J. Org. Chem. 1998 63 5587. 53 S. F. Martin and S. K. Bur Tetrahedron Lett. 1997 38 7641. Review a02437i 127 Nat. Prod. Rep. 2000 17 117–127

ISSN:0265-0568    

DOI:10.1039/a902437i

出版商:RSC    

年代:2000

数据来源: RSC

摘要:

Book reviews Protective Groups in Organic Synthesis Theodora W. Greene and Peter G. M. Wuts 3rd Edition Wiley- Interscience 1999 xxi + 777 pp. price £58.00 ISBN 0471160199 Few scientific books ever make it to a second addition. The fact that Protective Groups in Organic Synthesis has appeared in a third edition is a testament to its stature as one of the most useful handbooks to serve organic chemistry in recent decades. Aside from its bulk—and more of that in a moment—little had changed since the winning formula established in the first edition which appeared in 1981. Separate chapters deal with protection of each of the major functional groups. For each protecting group conditions for formation are cited followed by more extensive discussion of conditions for cleavage.The book is divided into 10 chapters. The first chapter considers the role of protecting groups in organic synthesis. The syntheses of himastatin and palytoxin are included to exemplify the importance of a viable protecting group strategy in the design of a complex target. I would not have chosen either for the simple reason that their synthesis has only ever been described in communications and monuments should have sturdier plinths. The next eight chapters deal successively with protection of the hydroxy group including 1,2- and 1,3-diols (229 pages) phenols and catechols (46 pages) the carbonyl group (75 pages) the carboxy group (52 pages) the thiol group (39 pages) the amino group (159 pages) the alkyne C–H (5 pages) and the phosphate group (40 pages).The book ends with 40 pages of reactivity charts which give a rough indication of the reactivity of a protected functionality towards 108 prototype reagents. The reactivity charts are essentially unchanged since the first and second editions. A total of 1050 protecting groups are included in 5350 citations covering the literature up to the end of 1997. Greene and Wuts is not bedtime reading. It is a comprehensive catalogue of protecting groups with little attempt at being critical. That it is useful is beyond question it must be one of the most cited secondary reference works in the synthetic literature. The third edition which exceeds the bulk of the second edition by 50% will be an essential tool in every synthetic laboratory. The book is reasonably priced. Philip Kocienski University of Glasgow UK 129 Nat. Prod. Rep. 2000 17 129

ISSN:0265-0568    

DOI:10.1039/a001bkry

出版商:RSC    

年代:2000

数据来源: RSC