Natural sesquiterpenoids Braulio M. Fraga Instituto de Productos Naturales y Agrobiología, CSIC, 38206-La Laguna, Tenerife, Canary Islands, Spain Covering: 1996 Previous review: 1997, 14, 145 1 Farnesane 2 Monocyclofarnesane 3 Bicyclofarnesane 4 Nanaimoane, acanthodorane and isoacanthodorane 5 Bisabolane 6 ·-Santalane and ‚-santalane 7 Trichothecane, cuparane, herbertane, laurane and gymnomitrane 8 Chamigrane 9 Carotane, acorane, cedrane, duprezianane, italicane and anisatin group 10 Cadinane, cubebane, copaane, oploponane, copabornane and picrotoxane 11 Himachalane, longipinane and longibornane 12 Caryophyllane, botrydiane and quadrane 13 Humulane, alliacane, pentalenane, hirsutane, lactarane, marasmane, precapnellane, capnellane, illudane and africanane 14 Germacrane 15 Elemane 16 Eudesmane, valerane, oppositane and manicolane 17 Vetispirane and nudenane 18 Eremophilane, chiloscyphane and bakkane 19 Guaiane, xanthane, pseudoguaiane, rotundane and patchoulane 20 Aromadendrane and bicyclogermacrane 21 Pinguisane 22 Miscellaneous sesquiterpenoids 23 References 1 Farnesane The structure of the hydrocarbon caparratriene has been determined as 1.This compound has been isolated from Ocotea caparrapi and possesses significant growth inhibitory activity against leukemia cells.1 The sesquiterpenes 5-hydroxy- 12-oxo-farnesol 2 and 5-acetoxy-12-hydroxyfarnesol 3 have been found in an extract of the aerial parts of Inula salsoloides. 2 A novel furanosesquiterpene 4 has been obtained from the soft coral Lobophytum catalai, which has been collected in the Andaman and Nicobar Islands.3 The structures of ‘primitive’ membranes have been shown to be formed by single-chain polyprenyl phosphates.4 Feeding experiments with labelled acetates have been used to show that the dorid nudibranches, such as Archidoris odhneri and Archidoris montereyensis, can biosynthesize terpenoid acid glycerides de novo.5 The biotransformation of the acyclic terpenoid (2E,6E)-farnesol by the plant pathogenic fungus Glomerella cingulata has been studied.6 The absolute configuration of (3S)-nerolidol, the precursor of the acyclic homoterpene 4,8-dimethylnona-1,3,7- triene, has been determined by GC–MS analysis of the homoterpene produced after feeding to various plants a mixture of equal amounts of labelled (3S)- and (3R)-nerolidol derivatives. 7 Two new farnesyl protein transferase inhibitors have been isolated from a Streptomyces strain.8 The stereochemical course of human protein-farnesyl transferase has been shown to be similar to that of FPP synthase.9,10 New farnesyl phosphonate derivatives of phenylalanine have been prepared and used as inhibitors of farnesyl protein transferase.11 The full paper on the chemistry and biology of cylindrols, novel inhibitors of Ras farnesyl protein transferase, has appeared.12 Syntheses of oxocrinol,13 ·-farnesene hydroperoxides14 and furoic acid15 have been reported, whilst chiral syntheses of (+)-ipomeamarone16 and of several hydroxylated farnesane sesquiterpenes17 have been described.The synthesis and biological evaluation of several farnesyldiphosphate derivatives have been carried out.18,19,20 The electron-transfer photoreaction between (E,E)-farnesol and 1,4-dicyanobenzene has been studied.21 (E)-Nerolidol has been employed as starting material in the preparation of racemic ambrox,22 whilst farnesyl acetate has been used in a chiral synthesis of the same compound, in which a lipase catalysed resolution of racemic drimane-8,11-diol is involved.23 2 Monocyclofarnesane Two novel cyclonerolidol derivatives 5 and 6 have been isolated from the liverwort Porella subobtusa.24 The new sesquiterpenes 7–9 have been found in an extract of the aerial parts of Artemisia chamaemelifolia.25 The new norisoprenoids 10–13 have been obtained from the leaves of Apollonias barbujana.26,27 Another compound of this latter type 14 has been isolated from Viburnum dilatatum.28 The structure of 10-normegastigmane glycoric acid has been determined as 15.This compound has been found in Glycosmis arborea.29,30 Several megastigmane glycosides have been isolated from Alangium premnifolium,31 Bunias orientalis,32 Cydonia vulgaris, 33 Pistia stratiotes34 and Vitis vinifera.35 The absolute configurations of rehmaionosides A–C, three ionone glycosides from Rehmannia glutinosa, have been determined by chemical and physicochemical methods.36 O O O O O O O O O O O R1 OH OR2 O O O H Ang = ; Epang = ; Meacr = Epmeacr = ; Mebu = ; Vali = Sen = ; (CO)Pri = ; Tig = 1 4 2 R1 = O; R2 = H 3 R1 = OH,H; R2 = Ac Fraga: Natural sesquiterpenoids 73The structure of an antibacterial sesquiterpene, previously obtained from Premna oligotricha, has been revised to 16 on the basis of its chemical synthesis.37 The total synthesis and the absolute configuration of riccardiphenols A and B have been reported.38 Syntheses of theaspirone and vitispirane have been devised.39 Two independent syntheses of the potent antiulcerogenic compound (+)-cassiol40,41 and its enantiomer (")- cassiol42 have been accomplished this year.The first enantioselective syntheses of (")-pallescensone and (")-ancistrodial have been reported.43 A rapid synthesis of an intermediate 17 for the preparation of monocyclofarnesyl derivatives has been described.44 The natural occurrence of abscisic acid in Portuguese heather honey has been determined by HPLC analysis.45 A conformational analysis of ABA analogues, produced by Cercospora cruenta, has been carried out.46 The role of the hydroxy group in the activity of abscisic acid has been evaluated using derivatives, with a methyl ether at C-1, in the bioassays.47 Optically active forms of oxygenated analogues of ABA have been tested to evaluate its biological activity.48 3 Bicyclofarnesane The isolation of isodrimenediol 18, a possible intermediate in the biosynthesis of drimane sesquiterpenes from Polyporus arcularius, has been described.49 The two novel endothelin type B receptor antagonists RES-1149-1 19, RES-1149-2 20,50 6-epi-albrassitrol 21 and 12-hydroxy-6-epi-albrassitrol 2251 have been obtained from Aspergillus species.Compound 20 has also been isolated together with 23 from another species of this genus, Aspergillus ustus.52 A revision of the absolute configuration of the drimane sesquiterpene 24 has been reported.This compound had been obtained from Aspergillus oryzae.53 The new sesquiterpene 2·-hydroxyisodrimeninol 25 has been found in cultures of a fungus of Pestalotiopsis genus, which is associated with species of Taxus.54 The epicuticular wax of the fern Nephrolepis biserrata contains the three drimane sesquiterpenes 26–28.55 A compound Sch-65676 29, which shows inhibitory activity against the cytomegalovirus protease, has been obtained from the fermentation broth of a fungal culture,56 whilst the substance BE-40644 30, a new inhibitor of the human thioredoxin system, has been found in cultures of an Actinoplanes species.57 The genus Stachybotrys is also a good source of novel endothelin receptor antagonists, such as the lactam 31, stachybocin A 32 and other analogues. 58,59,60 Another fungus Memnoniella echinata contains the new IMPase inhibitors ATCC 20998A 33 and ATCC 20998C.61 The levels of the sesquiterpenes polygodial and 9-deoxymuzigadial in the foliage of several New Zealand populations of Pseudowintera colorata have been determined using HPLC and NMR methods.62 Known drimane, bisabolane and pinguisane sesquiterpenes have been isolated from a cell suspension culture of the liverwort Porella vernicosa.63 The brown alga Dictyopteris undulata contains a new sesquiterpene-substituted benzoquinone with antifeedant properties, which has been named cyclozonarone 34.64 The novel sesquiterpenes deoxyspongiaquinone 35, (E)- chlorodeoxyspongiaquinone 36, spongiaquinol 37 and (E)- chlorodeoxyspongiaquinol 38 have been isolated from a marine sponge of the Euryspongia genus, collected at the Great Australian Bight.65 The five new drimane derivatives 39–43 have been obtained from the sponge Dysidea fusca,66 whilst the two sesquiterpenes 44 and 45 have been found in Dysidea fragilis, collected in the lagoon of Venice.67 The absolute OMe OH OH AcO CO2H OH OH OH O O HO OH HO OH AcO HO HO OH OH OH OH OH HO OH OH HO 7 8 14 5 6 7 D7(8) 8 D7(14) 9 10 11 12 13 14 15 O O C6H5(CO)O OH OH 16 17 O O HO CHO O O HO HO OH OH HO OH OH CHO O O O R1 R2 OH 18 19 20 24 25 21 R1 = b-OH,H; R2 = H 22 R1 = b-OH,H; R2 = OH 23 R1 = O; R2 = H 74 Natural Product Reports, 1998stereochemistry of puupehenone and related metabolites has been determined.68 A cytotoxic red dimer of this sesquiterpene, dipuupehedione 46, has been isolated from a New Caledonian marine sponge of the genus Hyrtios.69 A general strategy for the synthesis of drimane sesquiterpenes, exemplified by the preparation of siccanin, has been developed.70 A racemic synthesis of cinnamolide and methylenolactocin has been described,71 whilst the enantioselective synthesis of (+)-avarol and (+)-avarone,72,73 and that of their enantiomers,73 have been reported. A synthesis of various model compounds for the central tricyclic ring system of popolophuanone E has been described.74 4 Nanaimoane, acanthodorane and isoacanthodorane The biosynthesis of nanaimoal, acanthodoral and isoacanthodoral in the dorid nudibranch Acanthodoris nanaimoensis has been investigated.75 Studies of the synthesis of these sesquiterpenes have also been reported.76 5 Bisabolane Nidulal 47 is a new bisabolane sesquiterpene with biological activity, which has been found in an extract of the basidiomycete Nidula candida.77 Four new sesquiterpene polyol esters 48–51 have been isolated from Cremanthodium ellisi.78 Seven new sesquiterpenes 52–58 have been obtained from the aerial O O O O O O O CHO CHO HO OH HO HO HN O N N O OH O O O R1 AcO HO HO HO OH OH AcO R2 CHO CHO HO HO CO2H 29 30 31 32 33 26 R1 = R2 = H 27 R1 = OAc; R2 = H 28 R1 = H; R2 = OAc O O OMe O O OH HO OMe MeO OMe O O MeO OMe OH HO Cl Cl 34 35 36 37 38 O O O O O O O OAc OAc O O O O O O O O OH HO CO2H CHO HO HO OH 39 40 41 42 43 44 45 46 OHC O O O O OH R3 R4O H OH OAng R2O OH OR1 O(CO)Pri 47 48 R1 = R3 = R4 = H; R2 = (CO)Pri 49 R1 = Ac; R2 = R3 = H; R4 = (CO)Pri 50 R1 = Ac; R2 = (CO)Pri; R3 = R4 = H 51 R1 = R4 = H; R2 = (CO)Pri; R3 = OH Fraga: Natural sesquiterpenoids 75parts of Achillea cretica.79 The bisabolane derivative 59 has been found in an extract of the foliage of Fitzroya cupressoides, 80 whilst the bisabolane endoperoxides 60 and 61 have been isolated from the aerial parts of Eupatorium rufescens.These metabolites showed schizonticidal activity against Plasmodium falciparum.81 The gum exudates of Commiphora kua contain the new sesquiterpene 62.82 The isolation and structural determination of the bisabolane derivative 63 has been reported.This compound has been obtained from the heartwood of Juniperus formosana.83 The known antifouling sesquiterpene 3-isocyanotheotheonellin 64 has been found in extracts of four nudibranches of the family Phyllidiidae.84 The synthesis of turmeronol B has been accomplished.85 The ultraviolet irradiation of isoperezone acetate has been studied.86 6 ·-Santalane and ‚-santalane Two new sesquiterpenes ·-santaldiol 65 and ‚-santaldiol 66 have been obtained from the heartwood of Santalum insulare.87 A new enantiospecific synthesis of ·-santalane derivatives has been described.88 7 Trichothecane, cuparane, herbertane, laurane and gymnomitrane Trichothecinols A, B and C 67–69 are potent antitumor promoting sesquiterpenoids, which have been isolated from the fungus Trichothecium roseum.89 A study of tricoverroid stereoisomers, produced by another fungus Myrothecium verrucaria, has been carried out.90 The biosynthesis of the trichothecene 3-acetyldeoxynivalenol has been investigated.91 Enzymatic formation of multiple sesquiterpene skeletons, by genetic alteration of the trichodiene synthase active site, has been reported.92 15-Hydroxytrichodiene 70, produced by hydroxylation of trichodiene, has been obtained in transformed Nicotiana tabaccum cell suspension cultures, expressing a trichodiene synthase gene from Fusarium sporotrichioides.93 The results of these two last studies demonstrate that the alteration or introduction of a sesquiterpene gene can result in the formation of new sesquiterpene metabolites. The sesquiterpene hydrocarbons ‚-bazzanene, ·-barbatene and ‚-barbatene, which are characteristic constituents of liverworts, have been identified for the first time as components of a higher plant, Meum athamanticum.94 An enantioselective synthesis of (")-cuparene and (")-‰- cuparenol has been described.95 Two new herbertane sesquiterpenes 71 and 72 have been found in an extract of the liverwort Herbertus aduncus, whilst the known sesquiterpenes herbertene and ·-herbertenol have been obtained from Herbertus borealis.96 Total syntheses of herbertenediol,97 herbertenolide, ·-herbertenol, ‚-herbertenol,98 tochuinyl acetate and dihydrotochuinyl acetate have been reported.99 An enantiocontrolled100 and a racemic101 synthesis of filiformin have been described.A new gymnomitrane 73 and a novel norgymnomitrane derivative 74 have been isolated from the liverwort Jungermannia truncata, collected in Malaysia.102 CO2H CO2H O OH O O OH O O O OH O OH OH H HO H HO H AcO H HO H HO H AcO HO HO R 52 53 54 55 56 57 R = a-OH 58 R = b-OH OH H O O O O H H H H H H OH OH O OH H CN 59 60 61 62 63 64 OH OH OH OH 65 66 O R1 O O O OH R2 70 67 R1 = O; R2 = OH 68 R1 = a-OH,H; R2 = H 69 R1 = a-OH,H; R2 = OH OH OH R OH O H H 71 R = CHO 72 R = CO2Me 73 74 76 Natural Product Reports, 19988 Chamigrane A new approach to the synthesis of racemic ·-chamigrene has been reported.103 9 Carotane, acorane, cedrane, duprezianane, italicane and anisatin group The structure and stereochemistry of fersorin 75 and fersoridin 76 have been reported.These new carotane sesquiterpenes were obtained from the roots of giant fennel, a Ferula species.104 Another two compounds of this type, isoferuone and 2,3-epoxyakichenol, have been isolated from Ferula jaeschkeana.105 The chromatography of a methanolic extract of Acorus calamus gave six novel acorane derivatives 77–82, which were shown to inhibit the germination of lettuce seeds.106 Another acorane sesquiterpene 15-hydroxyacora-4(14),8-diene 83 has been obtained from the heartwood of Juniperus chinensis.107 This plant also contains a cedrane sesquiterpene, cedr-3-en- 15-ol 84 and a duprezianane derivative, junipercedrol 85.The latter possesses a new skeleton.108 Another species of this genus, Juniperus thurifera, produces the sesquiterpenes ·-duprezianene 86, ‚-duprezianene 87 and sesquithuriferol 88. This last compound was transformed by solvolytic rearrangement into 86 and 87, confirming the structure of the duprezianane skeleton by chemical methods.109 The biotransformation of cedrol and related compounds by Mucor plumbeus has been investigated.110 Racemic syntheses of ·-biotol, ‚-biotol111 and ƒ2-cedrene112 have been described.The oxidation of the hydrocarbon italicene has been studied.113 A novel sesquiterpene lactone, 3-benzoylpseudoanisatin 89, has been found in the pericarps of Illicium dunnianum.114 Another species of this genus, Illicium verum, contains the neurotropic sesquiterpenoids veranisatin A 90, veranisatin B and veranisatin C.115 10 Cadinane, cubebane, copaane, oplopanane, copabornane and picrotoxane The structure of 10-isocyano-4-cadinene has been determined as 91.This sesquiterpene has been found in extracts of nudibranches of the family Phyllidiidae and showed antifouling activity against larvae of Balanus amphitrite.84 Three new cadinane sesquiterpenes 92–94 have been identified as components of species of the genus Baccharis.116 Other compounds of this type, ·-hinokienol 95 and ‚-hinokienol 96, and the cubebane derivative 97 have been isolated from the leaf oil of Chamaecyparis obtusa.In this study, the absolute configurations of 95 and 96 were established by synthesis from (")- menthone.117 The sesquiterpene (+)-10·-hydroxy-4-muurolen- 3-one 98, a new inhibitor of leukotriene biosynthesis, has 75 R = H 76 R = OAng HO R O O OH R 81 R = a-H 82 R = b-OH 83 77 R = H 78 R = Ac O OR O O R 79 R = H 80 R = OH OH H H OH H OH H 8 9 15 84 86 D8(9) 87 D8(15) 85 88 O O O O OMe C6H5(CO)O O O O HO OH OH HO HO 89 90 H H H HO H OH H H OH H H OH NC O 91 92 93 94 HO H R O H OH 97 98 95 R = a-OH 96 R = b-OH Fraga: Natural sesquiterpenoids 77been obtained from fermentations of a Favolaschia species.118 Other inhibitors of this type have been found in Leutinellus cochleatus.119 The cadinane derivatives 99 and 100–102 have been isolated from Artemisia chamaemelifolia25 and Fitzroya cupressoides,80 respectively.The heartwood of Juniperus formosana contains (")-15-hydroxycalamenene 103.83 The sesquiterpene o-naphthoquinones 104–107 have been isolated from the root bark of Ulmus davidiana.Their antioxidative activities were determined by a thiobarbituric acid method using rat liver microsomes.120,121 Other antioxidative sesquiterpenes, 7-hydroxy-3,4-dihydrocadalin and 7-hydroxycadalin, have been found in the dried flowers of Heterotheca inuloides. These compounds also showed cytotoxic activity.122 The novel furanosesquiterpene 108 has been obtained from Bursera leptophloeos.123 Several sesquiterpene glycosides, which have been named alangicadinosides A–E, have been isolated from Alangium premnifolium.124 The absolute stereostructure of (1S,4S)-cis-5-hydroxycalamenene 109 has been revised to (1R,4R)-cis-5-hydroxycalamenene utilizing X-ray analysis.This compound has now been isolated from the liverwort Bazzania trilobata.125 The complete 1H and 13C NMR spectra of ‰-cadinene have been assigned. This sesquiterpene hydrocarbon has been obtained from a Juniperus species.126 Purifi- cation of (+)-‰-cadinene synthase from bacteria-inoculated Gossypium hirsutum has been reported,127 whilst the cloning and heterologous expression of a second (+)-‰-cadinene synthase from Gossypium arboreum have been described.128 Syntheses of oxo-T-cadinol,129 halipanicine,130 hibiscoquin one131 C and 7-demethyl-2-methoxy-calamenene132 have been accomplished. An asymmetric synthesis of (+)-apogossypol hexamethyl ether has been devised.133 An enantiomerically pure form of an intermediate in the synthesis of (+)-heptelidic acid has been prepared.134 A review on the structure, biosynthesis and functions of artemisinin (qinghaosu) has appeared.135 A new artemisinic acid analogue has been obtained from the mature stems of Tithonia diversifolia.136 The assignment of the 1H NMR signals of artemisinic acid has been revised,137 whilst the 13C NMR spectra of ·- and ‚-dihydroartemisinin have been assigned.138 The cytotoxicity of several artemisinin derivatives has been evaluated.139 The production of methyl 3-oxoartemisinate by biotransformation of methyl artemisinate with suspension cell cultures of Mentha piperita has been studied.140 The isolation of clones of Artemisia annua, containing high amounts of artemisinin141 and artemisinic acid142 have been reported.An immunoquantitative analysis of artemisinin using polyclonal antibodies has been developed.143 Ferrous ion induced the cleavage of the peroxy bond in artemisinin and its derivatives.DNA damage due to this process has been observed and may be responsible for the antimalarial activity of these substances. 144 On the other hand, the rearrangements of artemisinin in the presence of heme and non-heme iron(II) and iron(III) have been investigated.145,146 The biotransformation of the semisynthetic sesquiterpene artemether, using Cunninghamella elegans and Streptomyces lavendulae, has been studied.147 Novel asymmetric total syntheses of (+)-artemisinin,148 (")- artemisinin D and (")-arteannuin D149 have been described. A radiolabelled synthesis of 14C-artemisinin has been reported.150 The preparation of a new artemisinin dimer has been achieved.151 Artemisinic acid has been converted into (")-fabianane in seven steps.152 An eYcient total synthesis of (")-10-desmethylarteannuin B has been described.153 The novel sesquiterpenes 4-hydroxycopa-2-ene 110 and 2·-hydroxycopa-3-ene 111 have been obtained from a petrol extract of Entandrophragma cylindricum.154 Two new bioactive oplopanane derivatives tussilagonone 112 and neotussilagolactone 113 have been isolated from Tussilago farfara.155 The stereoselective synthesis of copaborneol by an intramolecular double Michael reaction has been reported.156 Picrotoximaesin 114 is a new sesquiterpene, which has been isolated from the berries of Maesobotrya floribunda.157 11 Himachalane, longipinane and longibornane A homosesquiterpene 3-methyl-·-himachalane 115 has been characterized as the main sex pheromone of Lutzomya H H HO O OH OH H R 99 102 103 100 R = a-OH 101 R = b-OH O O O OR2 R1 OH O O 107 104 R1 = CH2OH; R2 = Me 105 R1 = Me; R2 = CO2Me 106 R1 = Me; R2 = CH(OMe)2 O O OH 109 108 O O MeCH O MeCH HO OH H OH H OMebu H OMebu H H O O HO 110 111 112 113 114 78 Natural Product Reports, 1998longipalpis, a diptera from Brazil.158 The himachalane derivative 116 has been isolated from the foliage of Fitzroya cupressoides. 80 The structure of the sesquiterpene 117, which had been obtained from Cedrus atlantica, has been resolved by X-ray analysis.159 The leaves of Artemisia argyi (Chinese moxa) contain the novel longipinane derivative moxartenone 118.160 Other sesquiterpenes with this carbon framework ·-longipin-2-en-3-one 119 and 12-hydroxy-·-longipinene 120 have been isolated from Achillea millefolium161 and Juniperus chinensis,107,108 respectively.The acid rearrangement of longipinane into arteaganane has been studied,162 whilst the photochemical rearrangement of a longipinane derivative into a vulgarone derivative and a compound with a new tricyclic skeleton, has been investigated.163 The structure of isoculmorin has been determined as 121 by X-ray analysis.This compound has been obtained from the marine fungus Kallichroma tethys.164 A stereoselective synthesis of longiborneol has been reported.156 12 Caryophyllane, botrydiane and quadrane The sesquiterpenes pestalotiopsin A 122 and pestalotiopsin B 123 have been isolated from a Pestalotiopsis species, a fungus associated with the bark and leaves of Taxus brevifolia.165 A new trypanocidal sesquiterpene, lychnophoic acid 124, has been found in a species of the genus Lychnophora.166 The rearrangements of caryophyllene oxide in acid medium167 and in tetracyanoethylene168 have been studied.The gastric cytoprotection of the antiinflammatory sesquiterpene ‚- caryophyllene in rats has been investigated.169 (")-Clovane-2·,9‚-diol 125 is one of the components obtained from the aerial parts of Baeckea frutescens.170 Five novel bioactive sesquiterpenes, botryenalol 126, botryendial 127, methyl acetyl botryenaloate 128, 10-epi-dihydrobotrydial 129 and 10-dehydroxydihydrobotrydialone 130, have been isolated from cultures of the fungus Botrytis cinerea.171 Another two sesquiterpenes, previously isolated from this fungus, botrydial and dihydrobotrydial, appear to be responsible for the phytotoxic activity of this microorganism.172 The presilphiperfolane sesquiterpene 131, compound 132, formed by oxidative cleavage, and four silphiperfolane acids 133–136 have been isolated from Artemisia chamaemelifolia.25 A formal asymmetric total synthesis of (")-isocomene has been achieved,173 whilst a racemic synthesis of presilphiperfolan- 9-ol has been carried out.174 An extract of the gorgonian Subergorgia suberosa contains a novel cytotoxic sesquiterpene suberosenone 137.This is the first quadrane derivative found in a marine species.175 The molecular structure of terrecyclodiol 138, a derivative of the antifungal metabolite terrecyclic acid, has been determined by X-ray analysis.176 13 Humulane, alliacane, pentalenane, hirsutane, lactarane, marasmane, precapnellane, capnellane, illudane and africanane A highly functionalized humulane derivative 139 has been isolated from an endophytic fungus of Taxus brevifolia.177 The O H H O O H H H HO OAc 115 116 117 118 O H H H H H H OH OH OH 119 120 121 O CO2H H OH OMe AcO OH AcO HO OMe HO H 122 123 124 O O CHO R OAc H OH OH OAc H OAc H OH H HO OH O 125 129 130 126 R = CH2OH 127 R = CHO 128 R = CO2Me H H H OH H HO2C HO2C O O R R 131 132 133 R = a-OMe 134 R = b-OMe 135 R = a-Me 136 R = b-Me Fraga: Natural sesquiterpenoids 79total synthesis of two alliacane derivatives of marine origin has been carried out.178 A synthesis of racemic pentalenene has been reported.179 Four hirsutane derivatives 140–143 with antibiotic properties have been obtained from cultures of the fungus Lentinus crinitus.180 Racemic syntheses of ceratopicanol have been described.181,182 The syntheses of the linear and angular triquinane skeletons have been reported.183,184 Subvellerolactone C 144 is a new lactarane sesquiterpene, which has been found in an extract from the fruit bodies of Lactarius subvellereous.185 The trans-fused lactarane sesquiterpene 3-O-ethyl-8-epi-9-epi-furandiol has been synthesized and its structure determined by X-ray analysis.186,187 A reinvestigation of an ethanolic extract of Lactarius vellereus aVorded four new lactones with the marasmane skeleton 145–148.188 Two dialdehydes with this skeleton, merulidial and isovelleral, react stereoselectively with the natural triketide triacetic acid lactone giving pentacyclic pyranone adducts.One of these adducts, that formed with merulidial, was identical with a compound previously isolated from cultures of Merulius tremellosus.189 A concise total synthesis of dactylol and 3·-epi-dactylol has been devised.190 Two asymmetric syntheses of natural (")- ƒ9(12)-capnellene have been described.191,192 The structure of lentinellone has been determined as 149.This protoilludane derivative has been obtained from submerged cultures of Lentinellus cochleatus.193 Two new active metabolites against bacteria and phytopathogenic fungi, illudin C2 150 and illudin C3 151, have been found in a culture filtrate of Coprinus atramentarius.194 The design, synthesis and antitumor activity of bicyclic and isomeric analogues of illudin M have been reported.195 Normal and reverse phase HPLC methods have been established for the isolation of illudin M and illudin S, from extracts of fungi of the genus Omphalotus.196 An illudin S derivative, (hydroxymethyl)acylfulvene, has been shown to have antitumor properties.197 Two independent syntheses of the fern sesquiterpene pterosin Z have been carried out.198,199 An extract of the Colombian liverwort Porella swartziana contains five africanane derivatives, caespitenone 152 and swartzianin A–D 153–156, two secoafricanane sesquiterpenes, secoswartzianin A 157 and secoswartzianin B 158, and one norsecoafricanane norsecoswartzianin 159.200 Another africanane derivative 160 has been isolated from Porella subobtusa.24 The known sesquiterpene ƒ9(15)-africanane has been obtained from the soft coral Sinularia hirta.201 Dermatolactone 161 is a cytotoxic sesquiterpene with a novel carbon skeleton, which has been found in an extract of an Ascomycete belonging to the family Dermateaceae.202 O OH H H HO 137 138 O HO O OH R1 O H H R1 139 140 R1 = H; R2 = O 141 R1 = OH; R2 = O 142 R1 = H; R2 = a-OH,H 143 R1 = OH; R2 = a-OH,H O O H H O O H H O O R1 R1 O O HO OH H H Et O OH 144 145 146 147 R1 = H; R2 = OH 148 R1 = OH; R2 = H R O OH O H H OH OH 149 150 R = a-CH2OH 151 R = b-CH2OH O O O R O O MeO2C O O O HO HO H HO H O 152 155 156 157 158 159 153 R = H2 154 R = O O O O OAc O O H H 160 161 80 Natural Product Reports, 199814 Germacrane The structure of 9-methylgermacrane B has been determined to be a novel homosesquiterpene, which has been obtained from the sex pheromone glands of Lutzomyia longipalpis.203 The minimum energy conformations of two sex pheromones, periplanone A and periplanone B, of the American cockroach, Periplaneta americana, and of eleven structural analogues have been calculated using molecular mechanics methods.204 The hydrocarbon germacrene C is the main constituent of the liverwort Preissia quadrata, collected in Germany.205 Another liverwort Porella swartziana contains the germacrane diketone 162.200 The relative and absolute configuration of (+)- allohedycaryol 163 have been determined by synthesis of its enantiomer.206 This compound had been isolated from Ferula communis.Another species of this genus Ferula leucographa contains the new sesquiterpene leucoferin 164.207 Two novel sesquiterpenes, parvigemone 165 and neolitrane 166, have been found in an extract of the stems of Neolitsea parvigemma.208 The hydrocarbon germacrene A has been proposed to be an intermediate in the biosynthetic conversion of FPP to (")- aristolochene. Thus, when (7R)-6,7-dihydrofarnesyl diphosphate was incubated with aristolochene synthase dihydrogermacrene was obtained.209 The biotransformation of allylically activated (E,E)-cyclodeca-1,6-dienols by Cichorium intybus has been studied.210 Many new germacrane lactones have been isolated from natural sources during 1996.The structures 167–190 represent the new germacranolides, whilst the structures 191–202 have been assigned to the heliangolides, 203–205 to the melampolides, and 206 to the cis,cis-germacranolides (Table 1). There are several points to note in relation to these lactones.Known germacranolides have been obtained from Cyrtocymura cincta.214 The metabolites, mainly sesquiterpenes and sesquiterpene lactones, isolated from species of the subtribe Gochnatiinae (tribe Mutisieae, family Compositae) have been reviewed.222 The antiplasmodial activity and the cytotoxic eVects of aqueous extracts and sesquiterpene lactones from Neurolaena lobata have been evaluated.223 The antibacterial activity of several sesquiterpene lactones has been reported.224 Spectral data of chemical modification products of costunolide have been described.225 However, costunolide has been shown to have DNA-damaging properties.226 The structure of 1(10)Z,4Z-hanphyllin has been determined using X-ray analysis. 227 The acid cyclisation of 5-oxo-germacren-6,12-olide has been investigated.228 15 Elemane An investigation of the aerial parts of Onopordon myriacanthum aVorded the elemane derivative 207 and the elemanolide 208.217 The lactone 209 has been found as a component of the aerial parts of Centaurea nicaensis.229 Another compound of this type 210 has been obtained from the roots of Neolitsea hiiranensis,230 whilst the novel lactam clavulinin 211 has been isolated from the soft coral Clavularia inflata.231 16 Eudesmane, valerane, oppositane and manicolane Four new eudesmane sesquiterpenes 212–215 have been obtained from the liverwort Lepidozia vitrea,232 whilst the furan–eusdemane 216 has been isolated from another liverwort, Lophocolea heterophylla.233 The bisesquiterpene biatractylode 217 has been found in an extract of the Chinese medicinal herb Atractylodes marocephala.234 A study of Acorus calamus led to the isolation of the two sesquiterpenes 218 and 219.106 The aerial parts of Artemisia eriopoda235 and Artemisia mongolica236 contain the novel eudesmane derivatives 220–223 and 224, respectively. The structures 225 and 226 have been assigned to two metabolites isolated from Eremophila spectabilis. 237 Four new eudesmane derivatives pterodontic acid 227, 1‚-hydroxypterodontic acid 228, 3‚-hydroxypterodontic acid 229 and 2·,3‚-dihydroxypterodontic acid 230 have been found in the medicinal plant Laggera pterodonta.238 Another study of this plant aVorded other eudesmanes and eudesmanoic glucosides. 239 Eudesm-4(14)-en-3·,11-diol 231 is a new sesquiterpenoid, which has been found in the heartwood of Neocallitropsis pancheri.240 The structure of machikusanol has been determined as 232.This compound has been isolated from the xylem of Persea japonica.241 The new sesquiterpene 233, which possesses antibacterial activity has been obtained from Epaltes mexicana.242 An investigation of a hexane extract of the aerial parts of Pluchea quitoc yielded four novel eudesmane derivatives 234–237.243 Other novel products of this type 238 and 239 have been obtained from Senecio flammeus,244 and Tanacetum 162 163 O O OH 164 165 166 O O O O OAc OH O CO OH O OH O OAng O Table 1 Sources of germacrane lactones Source Ref.Germacranolides Anvillae garcinii 168, 169 211 Artemisia pallens 167 212 Carpesium nepalense 187–190 213 Eirmocephala megaphylla 170 214 Elephantopus mollis 172 215 Inula salsoloides 179–181 2 Mikania mendocina 186 216 Onopordon myriacanthum 171 217 Stevia maimarensis 173–178 218 Stevia vaga 182–185 219 Heliangolides Bajaranoa sp. 191–197 220 Mikania mendocina 198–199 216 Stevia vaga 200–202 219 Melampolides Inula salsoloides 203, 204 2 Stevia vaga 205 219 cis,cis-Germacranolides Acanthospermuim australe 206 221 Fraga: Natural sesquiterpenoids 81O O O O O O O O O O OH O O O O O O O O O OH HO O O OH O HO O O OR1 O O OH O O R O O O O O O R2 OAc OR3 R2 O OMeacr OAc OH O O O O O O O OAc O O O Cl O O O O O R3 O O O O O R2 OTig OH R1 R1 R2 OH HO OR OTig OH OH OR1 HO HO OH O O O O OAc O OH O O O OAc O O O CHO O O O O O (CO)Pri O OAc O O HO OR OH O O O R1 O HO 199 200 205 206 201 R = H 202 R = OAc 203 R = H 204 R = Vali 167 168 Partenolid-9-one 169 170 3-Deacylglaucolide B 171 172 173 R1 = R2 = H; R3 = OTig 174 R1 = H; R2 = OH; R3 = Tig 175 R1 = H; R2 = OH; R3 = 4-OHTig 176 R1 = OH; R2 = OAc; R3 = Tig 177 R1 = Tig; R2 = OH; R3 = H 178 186 197 198 179 R = H 180 R = OH 181 R = OAc 182 R1 = OAc; R2 = OH 183 R1 = OAc; R2 = H 184 R1 = H; R2 = OH 185 R1 = H; R2 = OAc 187 R1 = Sen; R2 = CH2 188 R1 = Ang; R2 = CH2 189 R1 = Tig; R2 = CH2 190 R1 = H; R2 = b-Me,H 191 R1 = H; R2 = 5-AcOTig; R3 = 192 R1 = H; R2 = 5-AcOTig; R3 = a-OH, b-CH2Cl 193 R1 = OH; R2 = Tig; R3 = 194 R1 = OH; R2 = Tig; R3 = a-OH, b-CH2Cl 195 R = Ang 196 R = Tig OAc H H H H CO2Me O O OH O OH OH O CO2Me O O O O N O OH O OH OH OH O O OH O H OH 207 208 209 210 211 3 4 216 217 212 D4(15); R = H 213 D4(15); R = b-OH 214 D3(4); R = H 215 D3(4); R = a-OAc 218 R = H 219 R = OH 15 O O O O O O OH OH OH R Rpraeteritum,245 respectively.A new dinorsesquiterpene guayulone 240 with fungistatic properties has been isolated from the resin of Parthenium argentatum.246 This species also contains five novel sesquiterpenes 241–245.247 The phytotoxic metabolite zingibertriol 246 has been found in the fungus Pyricularia oryzae.248 The structure of 5-O-acetylcuauhtemonyl- 6-O-2*,3*-epoxy-2*-methylbutyrate, isolated from Pluchea carolinensis, has been determined by X-ray analysis.249 This technique has been also used in the structural determination of emmotin-2 247.250 An eYcient and stereoselective synthesis of (+)-·-cyperone has been devised.251 (&)-Dihydrocarvone has been used as starting material in the synthesis of (+)-12-hydroxy-·- cyperone, (+)-12-oxo-·-cyperone and (+)-3-oxo-eudesma- 4,11(13)-dien-12-oic acid,252 whilst santonin has been employed in the preparation of (+)-‚-cyperone, eudesma-3,5- diene,253 furanoeudesma-1,3-diene and tubipofurane.254 A modified synthesis of racemic occidentalol has been reported.255 A practical synthesis of enantiomerically pure (")-geosmin has been achieved.256 Several dihydroagafuran sesquiterpenes have been obtained from members of the Celastraceae family: Celastrus flagellaris, 257 Celastrus hindsii,258 Celastrus orbiculatus259 and Maytenus buchananii.260 New eudesmanolides have been obtained from diVerent species (Table 2), and their structures shown to be 248–261.The cytotoxic and antibacterial activities of the sesquiterpene lactones isolated from Tanacetum praeteritum have been evaluated. 267 The 1H and 13C NMR assignment of the alantolactone moiety of the adduct of this lactone with (Z)-L-Cys-Ala-OMe has been reported.268 A short synthesis of the sesquiterpene lactone 1-oxoeudesma-2,4-dien-11‚,12,6·-olide has been achieved.269 A new (salen)-manganese(III) complex bearing a sesquiterpene salicylaldehyde derivative has been used in the CO2H CO2 H HO R R 227 R = H 228 R = OH 229 R = H 230 R = OH CO2Me OH OH OH OH O OH R O OH OH HO OH OH HO 220 221 224 225 226 222 R = O 223 R = b-OH,H OH O OOH EpangO HO HO 231 D4(15) 232 D4(5) 233 4 5 15 CO2Me O OH O O OH O HO OH OH AcO AngO AngO AngO AcO OH HO OH R 236 237 238 239 234 R = a-OH 235 R = b-OAc O OMe O O R1 MeO R2 OH OH HO CHO OH OH HO 240 247 241 R1 = Me; R2 = H2 242 R1 = H; R2 = H2 243 R1 = CH2OH; R2 = H2 244 R1 = Me; R2 = O 245 R1 = H; R2 = O 246 Table 2 Sources of eudesmanolides Source Eudesmanolides Ref.Artemisia giraldii 248 261 Artemisia herba-alba 249 262 Artemisia lerchiana 250, 251 263 Artemisia pontica 252–254 264 Inula salsoloides 255 2 Onopordon myriacanthum 257 217 Stevia maimarensis 256 218 Sarcandra glabra 261 265 Tanacetum praeteritum 258 245 Wedelia prostrata 259, 260 266 Fraga: Natural sesquiterpenoids 83catalysed epoxidation of unfunctionalized olefins with iodosylbenzene and molecular oxygen–pivalaldehyde as terminal oxidant.270 A HPLC method for the analysis of valerenic acids in extracts of Valeriana oYcinalis has been described.271 Enantiospecific syntheses of (+)-valerane and (")-valeranone have been achieved,272,273 while a racemic synthesis of isovalerenol has been reported.274 The sesquiterpene 262 has been isolated from the marine sponge Acanthella cavernosa.This compound inhibits the metamorphosis of Balanus amphitrite.275 A racemic synthesis of axamide and axisonitrile has been described,276 whilst enantioselective synthesis of (")- homalomelol A and homalomenol B has been reported.277 An enantiospecific construction of the carbon skeleton associated with the antineoplastic sesquiterpene manicol 263 has been accomplished.278 Spectral data of several eudemanolides obtained by epoxidation and cyclization of costunolide have been described.225 17 Vetispirane and nudenane The new sesquiterpene ethers 264 and 265 have been found in the apolar part of Haitian vetiver oil.279 The eVects of agarospirol and jinkoheremol, obtained from agarwood, on the central nervous system in mice have been investigated.280 A racemic synthesis of the spirovetivane phytoalexin (&)- lubiminol has been achieved,281 whilst an enantiospecific synthesis of (")-solavetivone has been carried out.282 The Taiwanese liverwort Mylia nuda contains the sesquiterpene nudenoic acid 266, which possesses a new carbon skeleton named nudenane, probably derived from vetisperane.283 18 Eremophilane, chiloscyphane and bakkane An eremophilane derivative 267 has been found in an extract of Pedicularis striata,284 whilst the new sesquiterpene ethers 268 and 269 have been isolated from vetiver oil.279 The structure of ligulaverin A 270 has been determined by X-ray analysis.This compound, which has been isolated from Ligularia veitchiana, possesses a new carbon framework possibly derived from an intramolecular Diels–Alder reaction of a hydroxymethylacrylate ester of an eremophilane sesquiterpene. 285 Another species of this genus, Ligularia virgaurea, contains the novel sesquiterpenes virgaurin A 271, furanomexican- 9-en-8-one and 9‚,10‚-epoxyfuranomexicanan-8- one.286 The phytotoxicity and the electrochemical properties of the herbicide cacalol and its derivatives, isolated from the roots of Psacalium decompositum, have been investigated.287,288 Four new dinoreremophilane derivatives with a rare skeleton eremopetasinorone A 272, eremopetasinorone B 273, eremopetasinol 274 and epoxyeremopetasinorol 275, and four novel eremophilenolides eremosulfoxinolide A 276, eremosulfoxinolide B 277, 3‚,8·-dihydroxy-6‚-methoxyeremophil- 7(11)-en-12,8-olide 278 and 2‚-hydroxyeremophil-7(11)-en- 12,8‚-olide 279 have been obtained from the rhizomes of O O O O O O O O O O O O O O O O O R R2 O O OH O O O O O(CO)Pri OH OH OR1 OH OH OH OH AcO OH OH O OR OH OH OH OR HO H H CHO R 248 249 252 R = various 257 258 261 250 R = CH2 251 R = a-OH,Me 253 R = b-OH 254 R = a-OVali 255 R1 = H; R2 = a-Me,H 256 R1 = various; R2 = CH2 259 R = Ang 260 R = Tig O O SCN HO O OH 262 263 O R CO2H 264 R = CH2 265 R = OMe,H 266 O O OH O O O O O OH O OH OH H O OH 267 268 269 270 271 84 Natural Product Reports, 1998Petasites japonicus.289 Another four lactones 280–283 and two new secoeremophilane derivatives, 284 and 285, were also isolated from this species.290,291 The roots of Roldana sessilifolia292 contain three new eremophilanolides 286–288.Another two compounds of this type have been obtained from Ligularia intermedia.293 The eremophilane derivative 289 has been found in Senecio hualtaranensis, whilst a closely related species, Senecio fabrisii, does not contain eremophilane derivatives.294 The chiloscyphane derivative 290 has been isolated from the liverwort Jungermannia vulcanicola.295 A highly stereoselective synthesis of an A-ring functionalized bakkane has been achieved.296 The synthesis of spirolactones related to the bakkenolides has been accomplished.297 19 Guaiane, xanthane, pseudoguaiane, rotundane and patchoulane Guaiswartzianin A 291 and guaiswartzianin B 292 are two guaiane sesquiterpenes, which have been isolated from Porella swartziana.200 The essential oil from the heartwood of Thuja occidentalis298 contains the two guaiane derivatives 293 and 294. A 1,5,11-trihydroxyguaiane has been isolated from Caryodaphnosis tonkinensis,299 whilst the compounds 295–297 have been obtained from Viburnum awabuki.300 Other guaiane derivatives valeracetate 298 and pancherione 299 have been obtained from Valeriana oYcinalis301 and Neocallitropsis pancheri,240 respectively. The bis-sesquiterpene assafulvenal 300, which is formed from a guaiane and a patchoulane sesquiterpene, has been isolated from the root bark of Joannesia princeps, and its structure has been determined by X-ray analysis.302 A guaiazulene pigment 301 has been found in the gorgonian Calicogorgia granulosa.303 Known guaiane derivatives have been obtained from Lepechinia urbaniana304 and Rubus rosifolius.305 Another known sesquiterpene with cytotoxic properties, guaianediol 302, has been isolated from the Red Sea soft coral Sinularia gardineri.306 Koike et al.307 have reported the synthesis of natural dictamnol, but later De Groot et al.308 have prepared cis-dictamnol stating that dictamnol has a trans- and not a cis-fused hydroazulene system.Thus, the structure of dictamnol (Nat. Prod. Rep., 1995, 12, 313, structure 273) has been revised to 303.The synthesis of (")- clavukerin A and (")-11-hydroxyguaiene has been achieved, but the spectroscopic data of the latter did not match with O O O O O OAng RO H H HO H R S O O S O O O O HO OMe H O O H HO H OH : : 5 6 272 R = a-Me 273 R = b-Me 274 275 5,6-epoxy 276 R = 277 R = 278 279 O O OAng H O O OR2 H R1 O O OH H OH O OH OAng O O OH OAng O OH O O O O HO HO OH OMe Cl O HO 280 283 284 285 281 R1 = OH; R2 = 282 R1 = R2 = H O O OH O O OH R O O(CO)Et H O O OH OAng OH OH 288 289 290 286 R = H 287 R = OH O O OH H H H HO 291 R = D4(15) 292 R = D3(4) 293 294 OH OH OH O OAc O OH H HOO HOO H H H H H H 295 296 297 298 299 Fraga: Natural sesquiterpenoids 85those reported for the natural compound.309 An asymmetric synthesis of the perhydroazulene (")-isoclavukerin A has been achieved.310 The sources of the new guaianolides 304–320 that have been isolated from plant species during the period of coverage of this review are listed in Table 3.A reinvestigation of the Caribbean sea plume, Pseudopterogorgia americana, aVorded the novel lactones americanolide A 321, americanolide B 323 and americanolide C 322.316 The structures of the guaianolides, canin, tanaparthin ·-peroxide, secotanapartholide A, artecanin, tanaparthin ‚-peroxide and secopartholide B, present in the feverfew, Tanacetum parthenium, have been revised by X-ray analysis and chemical correlations. The activity of some of these compounds as inhibitors of human blood platelet function has been determined, and its relation to migraine prophylaxis by feverfew has been discussed.317 Known guaianolides have been obtained from Artemisia pedemontana.318 The production and characterization of polyclonal antibodies against the bitter sesquiterpene lactones of chicory, Cichorium intybus, has been described.319 The crystal structure of 11‚,13-dihydromicheliolide has been reported.320 The absolute configuration of chlorojanerin has been determined by X-ray analysis.321 The circular dichroism spectra of eight guaianolides, obtained from Centaurea scoparia, have been studied.322 The new xanthanolide glycosides 324, 325 and 326, 327 have been isolated from the flowers of Arnica amplexicaulis323 and the aerial parts of Xanthium spinosum,324 respectively.The structure of the pseudoguaianolide hymenograndin B has been determined as 328. This lactone has been found in Hymenoxys brachyactis.325 A biosystematic study of Argentinian species of Gaillardia has been carried out, using the pseudoguaianolides as chemotaxonomical markers.326 A species of this genus, Gaillardia grandiflora,327 contains the new lactones 329 and 330.The cytotoxicity and the NMR spectral assignments of ergolide and bigelovin have been described.328 The phytotoxicity of parthenin on aquatic weeds has been studied.329 A formal enantiospecific synthesis of (+)-carpesiolin, (+)- confertin, (")-damsin, (")-helenalin, (+)-bigelovin, (+)- mexicanin I and (+)-linifolin A has been reported.330 The lactones rotundopontilides A–F 331 possess the uncommon rotundane skeleton.They have been obtained from the OHC H OH HO H H HO H 300 301 302 303 O O O O O O O O O O O O O O O O O O O O O O O O O O O OH O O OR2 R OAc R OAng H H HOH HO H H OMeacr H H H H OH OH GlcO H H HO HO H H OH OH H H O O O O O H HO H R1 R HO HO HO R OH 304 Moxartenolide 305 R = a-Me 306 R = b-Me 307 Gnaphaloide 308 R1 = a-CH2OH; R2 = H 309 R1 = a-CH2OH; R2 = Ac 310 R1 = b-CH2OH; R2 = H 311 R1 = b-CH2OH; R2 = Ac 312 313 314 315 318 323 321 R = OH 322 R = H 316 R = CH2 317 R = a-Me,H 319 R = CH2 320 R = a-OH,Me, Table 3 Sources of guaianolides Source Guaianolides Ref.Arnica mollis 313 311 Artemisia argyi 304 161 Artemisia lerchiana 314, 315 263 Crepis rhoeadifolia 305, 306 312 Mikania mendocina 316–318 216 Picris radicata 319, 320 313 Ptilostemmon gnaphaloides 307 314 Stevia vaga 308–311 219 Tanacetum argenteum 312 315 86 Natural Product Reports, 1998aerial parts of Artemisia pontica.331 The stereoselective synthesis of (&)-isonorpatchoulenol has been achieved.332 The asymmetric synthesis of vulgarolide and deoxocrispolide has been accomplished.333 20 Aromadendrane and bicyclogermacrane The sesquiterpene 332 has been isolated from the marine sponge Acanthella cavernosa. This compound inhibits the metamorphosis of the barnacle Balanus amphitrite.275 The new aromadendrane derivative isoplagiochilide 333 and the 2,3- secoaromandendrane 334 have been found as a constituent of the liverworts Plagiochila elegans334 and Heteroscyphus coalitus, 335 respectively.Three ent-alloaromadendranes 335–337, two ent-2,3-secoaromadendrane 338 and 339, and one bicyclogermacrane 340 have been obtained from cultured cells of Heteroscyphus planus.336 The first natural occurrence of the (")-ledol has been reported.This metabolite has been obtained from another liverwort, Cephaloziella recurvifolia.337 In a study of the constituents of Dicranolejeunea yoshinagana it has been observed that (")-spathunelol is an artefact formed from (")-ent-bicyclogermacrane, when it is allowed to stand at room temperature or during the extraction of liverworts.338 A total synthesis of (+)-ledol has been described.339 Stereoselective total syntheses of (+)-aromadendrane and (")- alloaromadendrane have been achieved.340 The biomimetic synthesis and absolute configuration of (")-tanzanene have been reported.341 The ozonolysis of (+)-aromadendrane and other terpenoids have been investigated.342 The rearrangements of ledene and aromadendrene in superacidic media have been studied.343 On the other hand, the rearrangement of (+)-ledene epoxide in acid medium has been described.344 21 Pinguisane Two novel pinguisane derivatives 341 and 342 have been obtained from the liverwort Dicranolejeunea yoshinagana.345 Another three new sesquiterpenes of this type 343–345 have been isolated from axenic cultures of Aneura pinguis.346 The structure and biosynthesis of several pinguisane sesquiterpenes have been reported.347 A novel pinguisanoic acid 346 has been found in an extract of the liverwort Porella platyphylla.348 In this work the stereochemistry of ‚-pinguisenediol has been revised to 347.Known pinguisane sesquiterpenes have been O O GlcO R O O R2O O O OR1 OAc H AcO AcO 326 R1 = H; R2 = Glc 327 R1 = Glc; R2 = H 328 324 R = a-Me 325 R = b-Me O O OH H HO RO OAc 329 R = H 330 R = Ang HO OR H O O 331 R = various O HO O O H H NCS H 332 333 334 335 R1 = R2 = H 336 R1 = H; R2 = Ac 337 R1 = R2 = Ac 338 339 340 H R1O AcO H O AcO H AcO H H HO AcO HO O OH R2O O R O O O O O O OR 341 R = CHO 342 R = CH2OAc 343 R = H 344 R = Me 345 O MeO2C OH OH OH 346 347 Fraga: Natural sesquiterpenoids 87obtained from another species of this genus, Porella vernicosa. 63 A racemic synthesis of ‚-pinguisene and pinguisenol has been described.349 22 Miscellaneous sesquiterpenoids The myltaylane derivative 348 has been found in the liverwort Bazzania trilobata.125 Benkarlaol 349 is a new sesquiterpene with a new skeleton, which has been isolated from a Chinese red alga Laurencia karlae.350 Rarisetenolide 350, epoxyrarisetenolide 351 and epirarisetenolide 352 are new sesquiterpene lactones with a new carbon framework, which have been obtained from the marine ciliated morphospecies Euplotes rariseta.These compounds are used by this organism as defensive agents.351 The novel antifouling sesquiterpenes isocyanotrachyopsane 353 and 10-epi-axoisonitride 354 have been found in a nudibranch of the family Phyllidiidae.84 The antiinflammatory and antipyretic activities of the sesquiterpene spartidienedione have been studied.352 Dimeric sesquiterpene thioalkaloids have been shown to have potent immunosuppressive properties.353 An HPLC method for the separation of bilobalide and ginkgolides has been described.354 (")-Furodysinin has been synthesized in enantiomeric355 and racemic356 forms.Syntheses of ent-herbasolide357 (&)-2- pupukeanone358 and tavacpallescencin359 have been reported. 23 References 1 E. 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