14 Biological Chemistry Part (i) Biosynthesis By J. R. HANSON School of Molecular Sciences University of Sussex Brighton BN 1 9QJ 1 Introduction This report covers the period since 1975l and is of necessity highly selective. The fourth and fifth volumes of the Chemical Society’s Specialist Periodical Report on Biosynthesis have appeared. The period has been dominated by the application of C n.m.r. whilst examples have also begun to appear using 2H 3H,and ”N n.m.r. However these still complement rather than displace radio-isotopic techniques. Computer methods which have been used2 to generate skeleta based on a limited number of plausible biogenetic reactions illustrate the wide variety of possible skeletal types and the consequent limitations of ‘biogenetic analogy’ in structural reasoning.These methods have also been used3 to predict the distribution of label arising from different plausible biogenetic schemes. In a review lecture Birch has disc~ssed,~ inter alia the possibilities of analogue biosynthesis which is attracting attention in a number of fields (e.g. gibberellins ergot alkaloids gliotoxin). A useful review of the stereospecific synthesis of 3H-labelled organic compounds describes’ the preparation of many biosynthetic intermediates. The preparation of chiral acetic acid from glycine has been described.6 2 Polyketides Deuterium has been as a tracer in a study of terrein (1)biosynthesis. The isotope was located using 2H-’3C coupling patterns. The intact incorporation of the starter CD3C02- group was established from the isotope shift of the 13C resonance in the *H-decoupled spectrum.The superposition of two 13C-13C coupling patterns in R. B. Boar and D. A. Widdowson Ann. Reports (B),1975,72,415. * D. H. Smith and R. E. Carhart Tetrahedron 1976,32,2513. T. H. Varkony D. H. Smith and C. Djerassi Tetrahedron 1978 34 841. A. J. Birch Pure Appl. Chem. 1978,50 1005. D.W. Young in ‘Isotopes in Organic Chemistry’ Vol. 4 ed. E. Buncel and C. C. Lee Elsevier Amsterdam 1978 p. 177. ‘M. Kajiwara S.-F. Lee A. I. Scott M. Akhtar C. R. Jones and P. M. Jordan J.C.S. Chem. Comm. 1978,967. ’ M.J. Garson R. A. Hill and J. Staunton J.C.S. Chem. Comm. 1977,624. M.J. Garson R. A. Hill and J. Staunton J.C.S. Chem. Comm. 1977 921. 329 330 J.R. Hanson the fungal metabolite scytalone (2) biosynthesized from [13C2]acetate impliesg a symmetrical precursor such as (3).A similar effect has been noted" in the biosyn- thesis of secalonic acid A in which the labelling pattern is in accord with a benzophenone intermediate which can reach rotational equilibrium before dimerization. The 2H-'3C isotope shift and coupling pattern was also usedg'" to locate the site of an [2-2H3 2-13C] acetate label in scytalone. OH 0 OH OH HO HOfyJ HOfyJ O"i" OH ' OH ' OH (1) (2) (3) A number of pathways involving either the folding of a polyketide of six acetate units or two separate polyketide residues have been for the biosyn- thesis of the fungal metabolite sclerin (5). However the [13C2]acetate labelling pattern and the incorporation of a sclerotinin A (4) suggestt4 that it is a pentaketide formed by a novel cleavage and recyclization sequence.On the other hand two initial chains may be involved" in the biosynthesis of citromycetin (6). Scheme 1 The biosynthesis of the antibiotic griseofulvin (9) was one of the first examples to be studied by 14C labelling. The incorporation of 13C-labelled acetate via a U. Sankawa H. Shimada T. Sato T. Kinashita and K. Yamasaki Tetrahedron Letters 1977,483; H. Set0 and H. Yonehara ibid. 1977,487. lo I. Kurobane L. C. Vining A. G. McInnes J. A. Walker and J. L. C. Wright Tetrahedron Letters 1978 1379. U. Sankawa H. Shimada and K. Yamasaki Tetrahedron Letters 1978,3375. R. E. Cox and J:S.E. Holker J.C.S. Perkin I 1976 2077. I3 M. Yamazaki Y. Maebayashi and T. Tokoroyama Tetrahedron Letters 1977,489. I4 M. J. Garson and J. Staunton J.C.S. Chem. Comm. 1977,928; 1978 158. G. E. Evans and J. Staunton J.C.S. Chem. Comm. 1976,760. Biological Chemistry 33 1 heptaketide chain has been described.I6 The benzophenone griseophenone B(7)," which possesses two free hydroxyl groups in ring A,has a key role in the oxidative coupling to form normethyldehydrogriseofulvin (8). 2H n.m.r. spectroscopy has been used" to show that griseofulvin is biosynthesized with the 5'a-configura-tion of deuterium from [5'-2H]griseophenone B and 4-demethyl-[5'-2H]de-hydrogriseofulvin. The last reductive step in the biosynthesis takes place with a trans diaxial addition of hydrogen.CI CI (7) The aflatoxins continue to attract attention.' The [13C]acetate labelling pattern implicated" a single polyketide chain in the biosynthesis of aflatoxin B1 whilst evidence has been presented for the formation of averufin versiconal acetate (11),21and versicolorin A (12)22from [13C]acetate and for their role (Scheme 2) together with that of sterigmatocystin in aflatoxin B1(13)biosynthesis. 0 CH3-C02-O -HO ~ ~ ~ ~0 ~ 0 HO 0 HO OH 0 OH (10) / (11) OH 0 OH 00 '' T. J. Simpson and J. S. E. Holker Phytochemistry 1977,16,229. C. M. Harris J. S. Robertson and T. M. Harris J. Amer. Chem. SOC. 1976,98,5380. " Y. Sato T. Oda and H. Saito J.C.S. Chem. Comm. 1977,415; 1978 135. l9 D. P.H. Hsieh R. C. Yao D.L. Fitzell and C. A. Reece J. Amer. Chem. Soc. 1976,98 1020. *' C.P. Gorst-Allman K. G. R. Pachler P. S. Steyn P. L. Wessels andD. BuysScott,J.CS. Chem. Comm. 1976,916;J.C.S. Perkin I 1977,2181. R.H. Cox F. Churchill R. J. Cole and J. W. Dorner J. Amer. Chem. Soc. 1977,99 3159. '* C. P. Gorst-Allman P. S. Steyn P. L. Wessels and D. Buys Scott J.C.S. Perkin I 1978 961 and refs. therein. 332 J. R. Hanson The assembly pattern of acetate units in the phenalenone system of deoxy-herqueinone (14) indicates23 a biosynthesis (Scheme 3)from seven acetate units and an isoprene unit. Malonate feeding results showed a clear acetate starter effect. Amongst many other 13C n.m.r. labelling studies which have been reported are those on the fungal xanthone ravenelin which is biosynthesized purely from acetate rather than shikimate chartreu~in,~~ daunomycin,26 dothi~tromin,~~ lankacidin C," molli~in,~~ and ~anthomegnin.~' (14) Scheme 3 The stereochemistry of incorporation of chirally labelled acetate and malonate into fatty acids has been de~cribed.~~ A higher proportion of label was retained in palmitic acid from the (S)-[2-'4C,2-2H,2-3H]acetyl CoA and (S)-[U-I4C,2-3H]malonyl CoA than from the (R)-epimers.Arachidonic acid (15) forms a key intermediate in the biosyn thesis (Scheme 4) of the prostaglandins prostacyclins and thromboxanes -a subject which has been extensively re~iewed.~' 3 Terpenoids The biosynthesis of 3-hydroxy-3-ethylglutarate and 3-homomevalonic acid precursors of the insect juvenile hormone has been e~tablished~~ in the insect Manduca sexta.The prenyltransferase reaction involving the 1'4-coupling of isoprene units has been extensively and evidence presented for an ionization :condensation :elimination sequence (Scheme 5). Prenyltransferase does not have a very stringent substrate specificity. The coupling of the methylated 23 T. J. Simpson J.C.S. Chem. Comm. 1976,258. 24-A.J. Birch J. Baldas J. R. Hlubucek T. J. Simpson and P. W. Westerman J.C.S. Perkin I 1976,898. 25 P. Canham L. C. Vining A. G. McInnes J. A. Walter and J. L. C. Wright J.C.S. Chem. Comm. 1976 319. 26 R. C. Paulick M. L. Casey and H. W. Whitlock J. Amer. Chem. SOC. 1976,98 3370. 27 G. J. Shaw M. Chick and R. Hodges Phytochemistry 1978,17 1743.28 M. Uramoto N. Otake L. Cary and M. Tanabe J. Amer. Chem. SOC.,1978,100,3616. 29 M. L. Casey R. C. Paulick and H. W. Whitlock J. Amer. Chem. SOC., 1976,98,2636. 30 T. J. Simpson J.C.S. Perkin I 1977 592. 31 B. Sedgwick and J. W. Cornforth EuropeanJ.Biochem. 1977,75,465;B. Sedgwick J. W. Cornforth S. J. French R. T. Gray E. Kelstrup and P. Willadsen European J. Biochem. 1977,75481. 32 see for example K. H. Gibson Chem. SOC. Rev. 1977,6,489. 33 F. C. Baker and D. A. Schooley,J.C.S. Chem. Comm. 1978,292;E.Lee D. A. Schooley M. S. Hall and K. J. Judy ibid.,p. 290. 34 for a review see C. D. Poulter and H. C. Rilling Accounts Chem. Res. 1978 11 307. Biological Chemistry C02H OH OH PGHZ TXAp 0 Hd \?4 CO,H 2aA+- OH OH OH OH PGF2 PGI2 Scheme 4 LOPP -/&/+ R R\ L+OPP OPP 1 OPP (PP =P*o6-) Scheme 5 334 J.R. Hanson analogue (16) of isopentenyl pyrophosphate with dimethylallyl pyrophosphate afforded3’ (4S,8S)-4,8-dimethylfarnesol (17) revealing the latent stereospecificity of this process. CH H CH (16) (17) The biosynthesis of aromatic hemiterpenoids has been reviewed.36 The incorporation of [l3C2]acetate into flavoglaucin has shown that in this case of aromatic isoprenylation there was no change in the stereochemistry of the olefin in the dimethylallyl moiety.37 Cell-free extracts of monoterpenoid-producing plants contain3* ‘salvage’ enzyme systems which convert prenyl pyrophosphates such as isopentenyl pyrophosphate into water-soluble products such as 3-methyl-3,4-oxidobutan-l-ol and the cor- responding triol.The biosynthesis of the thujane skeleton from geraniol and nerol which are interconverted by a redox process has continued to attract attention.39 However tracer from geraniol and nerol was incorp~rated~~ into the irregular monoterpene artemisiaketone (18) with extensive scrambling in contrast to the incorporation into regular monoterpenoids such as isothujone (19). The hydrolysis of the C-0 bond of truns,truns-farnesyl pyrophosphate (20) in Androgruphis tissue culture takes place41 with retention of configuration. Using the cyclization to cyclonerodiol(22) to reveal the stereochemistry the isomerization of farnesyl pyrophosphate to nerolidyl pyrophosphate (21)has been shown to occur42 with a syn (suprafacial) stereochemistry (Scheme 6).[l3C2]Acetate and mevalonate studies have been used to define the folding of farnesyl pyrophosphate in the formation of a number of sesquiterpenoids including f~mannosin,~~ tri~hothecin,~~ and illudin M.45 Examination of the [4,5-13C2]mevalonate coupling and the induced 35 T. Koyama K. Ogura and S. Seto J. Amer. Chem. SOC.,1977,99 1999. 36 M. F.Grundon Tetrahedron 1978,34,143. ’’ J. K. Allen K. D. Barrow A. J. Jones and P. Hanisch J.C.S. Perkin I 1978 152. 38 D.V. Banthorpe G. A. Bucknall J. A. Gutowski and M. G. Rowan Phytochemistry 1977,16,355. 39 D.V. Banthorpe J. Mann and I. Poots Phytochemistry 1977,16,547;D. V. Banthorpe 0.Ekundayo and M. G. Rowan Phytochemistry 1978,17,1111;D.V. Banthorpe B. M. Modawi I. Poots and M. G. Rowan ibid. p. 1115. 40 K.G. Allen D. V. Banthorpe B. V. Charlwood and C. M. Voller Phytochemistry 1977,16,79;D. V. Banthorpe B. V. Charlwood G. M. Greaves and C. M. Voller ibid. p. 1387. 41 H.Mackie and K. H. Overton European J. Biochem. 1977,77 101. 42 D.E.Cane R. Iyengar andM.-S. Shiao J. Amer. Chem. SOC. 1978,100,7122. 43 D.E.Cane and R. B. Nachbar Tetrahedron Letters 1976,2097;J. Amer. Chem. SOC. 1978,100,3208. 44 B. Dockerill J. R. Hanson and M. Siverns Phytochemistry 1978 17 427. 45 A. P.W. Bradshaw J. R. Hanson and M. Siverns J.C.S. Chem. Comm. 1978,303. Biological Chemistry Ill DJ :$OH H OH Scheme 6 couplings between centres enriched by flooding a system with [13C]acetate has been to define the folding of farnesyl pyrophosphate in the biosynthesis of dihydrobotrydial (23).U AcO The application of 2H n.m.r. to the biosynthesis of ovalicin (24) enabled4’ the labels from [5-2H]mevalonate to be located. The fate of mevalonoid hydrogen in ‘OCH 0 (24) 46 A. P. W. Bradshaw J. R. Hanson and M. Siverns,J.C.S. Chem. Comm. 1977,819;J. R. Hanson and R. Nyfeler J.C.S. Chem. Comm. 1976,72. ‘’D. E. Cane and S. L. Buchwald J. Amer. Chem. Soc. 1977,99 6132. 336 J.R. Hanson the biosynthesis of the sesquiterpenoids culmorin cyclonerodiol illudin M tri-chodiene and trichothecin has been determined using 3H:14C ratio In another application of ’H n.m.r. to biosynthetic studies the stereochemistry of the SN2’ process involved in the allylic displacement of the pyrophosphate (25) to form rosenonolactone (26) has been to take place with an overall anti-stereochemistry (Scheme 7).The biosynthesis of the gibberellin plant hormones has H Scheme 7 continued to attract attention in both the chemical and biological literature.” l80 Studies have showns1 that both the oxygen atoms of the 19-carboxylic acid grouping in (27) are incorporated into the 19,lO-y-lactone bridge of the CI9 gibberellins e.g. (28) whilst the C-20 carbon atom is liberateds2 as carbon dioxide. The substrate g-$J moH . HO !H H *PC02HCHZoH CO H (27) (28) specificity of a number of steps in gibberellin biosynthesis has been examined53 using variously substituted including fluorinated kaurenoid substrates.The effect of deuterium on the 13C n.m.r. spectrum has been to distinguish between different hydride shifts in the cyclization of geranylgeranyl pyrophosphate to form fusicoccin. A demonstration that presqualene pyrophosphate is an obligatory intermediate in squalene biosynthesis utilized” the homologous phosphonophosphate analogue as a 48 R. Evans and J. R. Hanson J.C.S. Perkin I 1976,326; J. R. Hanson T. Marten and R. Nyfeler ibid.,p. 876; R. Evans J. R. Hanson. and R. Nyfeler ibid. 1976,1214; R. Evans J. R. Hanson and T. Marten ibid. p. 1212; J. R. Hanson and R. Nyfeler ibid. p. 2471. 49 D. E. Cane and P. P. N. Murthy J. Amer. Chem. SOC.,1977,99,8327. J. R. Bearder and V. M. Sponsel Biochem. Soc. Trans.1977,5,569; P. Hedden J. MacMillan and B. 0. Phinney Ann. Rev. Plant Physiol. 1978 29 149; J. MacMillan Pure Appl. Chem. 1978 50 995. ” J. R. Beader J. MacMillan and B. 0.Phinney J.C.S. Chem. Comm. 1976 834. ’’ B. Dockerill R. Evans and J. R. Hanson J.C.S. Chem. Comm. 1977,919. 53 M. W. Lunnon J. MacMillan and B. 0.Phinney J.C.S. Perkin I 1977,2308;B. M. Fraga J. R. Hanson and M. Hernandez Phytochemistry 1978,17,812;B. E. Cross and A. Erasmuson,J.C.S. Chem. Comm. 1978 1013. s4 A. Banerji R. Hunter G. Mellows K.-Y.Sim and D. H. R. Barton J.C.S. Chem. Comm. 1978,843. ” E. J. Corey and R. P. Volante J. Amer. Chem. SOC., 1976,98 1291. Biological Chemistry competitive inhibitor. In contrast to prenyltransferase squalene synthetase shows a marked substrate specificity.The C-3 methyl groups of farnesyl pyrophosphate are required56 whilst 2-methylfarnesyl pyrophosphate differentiates between the two binding sites of squalene synthetase affording only an 11-monomethylsqualene and not a dirnethylsq~alene.~~ The biosynthesis of sterols in photosynthetic organisms proceeds through cyclo- artenol (29) in contrast to non-photosynthetic organisms which utilize lanosterol (30). The formation of the cyclopropane ring in cycloartenol (29) may occur with inversion or retention of configuration. The use of chiral labelled oxidosqualene and 3Hn.m.r. has that the process involves retention of configuration (Scheme 8). The mechanism of cleavage of the ring has been studieds9 in the formation of obtusifoliol (31) from cycloeucalenol.H HO The removal6' of the 14a-methyl group of lanosterol (30) in cholesterol biosyn- thesis involves the C-32 aldehyde and the loss of the carbon atom as formic acid. Demethylation at C-4 involves the loss firstly of the 4a-methyl group via a P-keto-acid and then the original 4P-methyl group is epimerized to afford a C-4a-monomethyl sterol. The demethylation of this in obtusifoliol(31) results in the axial 4P-hydrogen atom being inverted into the equatorial 4a-position of the 4-desmethyl product poriferasterol.61 The loss of the C-19 group in oestrogen biosynthesis proceeds via the C-19 aldehyde and leads to the liberation of formic acid which acquires an "0label from oxygen gas implicating a Baeyer-VilIiger type 36 P.R. Ortiz de Montellano R. Castillo W. Vinson and J. S. Wei J. Amer. Chem. SOC. 1976,98,3020;W. N. Washburn and R. Kow Tetrahedron Letters 1977 1555. 57 P. R. Ortiz de Montellano R. Castillo W. Vinson and J. S. Wei J. Amer. Chem. SOC. 1976,98,2018. 58 L. J. Altman C. Y. Han A. Bertolino G. Handy D. Laungani W. Muller S. Schwartz D. Shanker W. H. de Wolf and F. Yang J. Amer. Chem. Soc. 1978 100 3235. 59 A. Rahier L. Cattel and P. Benveniste Phytochemistry 1977,16 1187. 60 M. Akhtar K. Alexander R. B. Boar J. F. McGhie and D. H. R. Barton Biochem. J. 1978,169,449. 61 F. F. Knapp L. J. Goad andT. W. Goodwin Phytochemistry 1977,16 1677. 338 J. R. Hanson of mechanism for this step.62 13C n.m.r. studies have been reported on cholesterol biosynthesized from [f3C]mevalonates.The labelling pattern of the side chain (32) indicates that in its formation by reduction of the 24,25-double bond the hydrogen atoms are added from the re The stereochemistry of hydrogen migration from C-24 to C-25 during isofucosterol bio~ynthesis~~ and the sequence involved in the elaboration of the phytosterol side chain6' have been studied. The cyclization of the carotenoid lycopene (33) to zeaxanthin (34) in a Flauobac-terium species grown in 2H20has been shown66 to occur with the initial attack of a proton (deuteron) on the re-faceof the 1,2-double bond. from 3'Me MvA 4 Shikimic Acid Metabolites An extensive review of the shikimic acid pathway has appea~ed.~' The stereo- chemistry of isoflavone reduction during the biosynthesis of the phytoalexin demethylhomopterocarpin (35) has been studied6' by 2H n.m.r.Evidence based69 on the feeding of cinnamic acids shows that various procyanidin dimers are biosyn- thesized from two metabolically distinct units (+)-catechin or (-)-epicatechin and the C-4 carbo-cation derived by protonation of flav-3-en-3-01s. Naturally occurring xanthones are commonly biosynthesized uia benzophenones derived from polyketides in fungi24 and shikimate polyketides in plants. The intact incorporation of a c&3 unit p-coumaric acid (as opposed to c&1 unit) into mangiferin (36) has been demonstrated" in Anemarrhena asphoeliodes. M. Akhtar D. Corina J. Pratt and T. Smith J.C.S. Chem. Comm. 1976 854. 63 G.Popjhk J. Edmond F.A. L. Anet and N. R. Easton J. Amer. Chem. SOC. 1977,W. 931. F.Nicotra F.Ronchetti G. Russo,G. Lugaro and M. Casellato J.C.S. Chem. Comm. 1977 889. " C.Largeau. L. J. Goad and T. W. Goodwin Phyrochemisfry 1977,16 1925. " G.Britton W. J. S. Lockley N. J. Patel T. W. Goodwin and G. Englert J.C.S. Chem. Comm. 1977 655. '' B. Ganem Tetrahedron 1978,34 3353. P. M.Dewick and D. Ward J.C.S. Chem. Comm. 1977,338;Phytochemistry 1978,17,1751. 69 E.Haslam Phytochemistry 1977 16 1625; E.Haslam C. T. Opie and L. J. Parter ibid. p. 99;D. Jacques C. T.Opie L. J. Porter and E. Haslam J.C.S. Perkin I 1977. 1637. 'O M.Fujita and T. Inoue Tetrahedron Letters 1977,4503. Biological Chemistry 339 5 Alkaloid Biosynthesis The mode of incorporation of lysine into securinine (37)has shown7' that the piperidine ring is formed in an unsymmetrical manner.The results of a study7* of the biosynthesis of the lupin alkaloid lupanine suggest that it is formed from lysine via an isotripiperideine. Reticuline (38)is an established precursor of a large number of benzylisoquinoline alkaloids. Although tyrosine contribute^^^ to the formation of both portions dopa & M::J3$Me Me0 ' H OH (37) (38) and dopamine afford the phenylethylamine portion whilst the benzylic portion is derived from 3,4-dihydroxyphenylpyruvicacid. Both enantiomers of reticuline are incorp~rated~~ into the morphinandienone alkaloid sebiferine (39)through the intervention of a redox system which allows the epimerization of the (+) to the (-)-form.Tracer experiments have been on the incorporation of (+)-norprotosinomenine into the abnormal Erythrina alkaloids such as isococculidine. The specific incorporation of phenylalanine into cephalotaxine (40) has shown that the cyclopentene arises76 by the loss of one carbon atom from the aromatic ring of OMe Me0 0 0 phenylalanine. The incorporation of tyrosine cinnamic acid and some later inter- mediates into the mesembrine alkaloids has been Several groups have 71 W. M. Golebiewski P. Horsewood and 1. D. Spenser J.C.S. Chem. Comm. 1976,217. 72 W. M. Golebiewski and I. D. Spenser J. Amer. Chem. SOC.,1976,98,6726. 73 D. S. Bhakuni A. N. Singh S. Tewari and R. S. Kapil J.C.S.Perkin I 1977 1662. 74 D. S. Bhakuni V. M. Mangla A. N. Singh and R.S. Kapil J.C.S. Perkin I 1978 267. 75 D. S. Bhakuni A. N. Singh and R. S. Kapil J.C.S. Chem. Comm. 1977,211. 76 J. N. Schwab M. N. T. Chang and R. J. Parry J. Amer. Chem. SOC.,1977,99,2368. 77 P. W. Jeffs D. B. Johnson N. H. Martin and B. S. Rauckman,J.C.S. Chem. Comm. 1976,82; P. W. Jeffs and J. M. Karle. ibid. 1977,60; P. W. Jeffs J. M. Karle andN. H. Martin Phyrochemistry,1978,17,719. 340 J. R. Hanson shown7' that in contrast to previous work the key precursor of the indole alkaloids which arises from tryptamine and secologanin is (3s)-strictosidine (41) and not its (3R)-epimer. Strictosidine is the common precursor for both the 3a- and 3P-indole alkaloids. The corresponding 3a-isomer in the condensation of dopamine and secologanin acts as the precursor of the Ipecac alkaloid^.^' Cathenamine (42),which accumulates in cell-free preparations from Catharanthus roseus in the absence of NADPH is incorporatedso into ajmalicine.The biosynthesis of the ergot alkaloids has been reviewed.81 6 Other Amino-acid Derived Metabolites The biosynthesis of the p-lactam antibiotics has been thoroughly reviewed.82 The tripeptide 8-(L-a-aminoadipy1)-L-cysteinyl-D-valine is a key intermediate in peni- cillin biosynthesis. Since the configuration at C-3 of penicillin is 'D',an inversion takes place on the incorporation of L-valine. Although the a-hydrogen of L-valine is lost in this process I5N n.m.r. studies have now confirmed83 that the N atom is retained. The feeding of stereospecifically labelled cysteines has shown that the cyclization to give the p-lactam ring of the penicillin^^^ and cephalo~porins~~ proceeds with the loss of the 3-pro-S-hydrogen and the retention of the 3-pro-R- hydrogen of cysteine.Thus there is net retention of stereochemistry in the cycliza- tion. Cyclo-(L-phenylalanyl-L-seryl) has been showns6 to be an intermediate in the biosynthesis of gliotoxin. Cyclo-(L-alanyl-L-phenylalanyl) is efficiently con-verted8' into 3a-deoxygliotoxin in an analogue biosynthesis in Trichoderma uiride. The biosynthesis of the porphyrins was extensively reviewed in last year's Annual Repord8 and hence is only briefly mentioned here. Other reviews have also appea~ed.~~.~~ Further evidenceg1 has been presented showing that the 78 J. Stockigt and M.H. Zenk J.C.S. Chem. Comm. 1977,646;M. Rueffer N. Nagakura and M. H. Zenk Tetrahedron Letters 1978 1593; R. T. Brown J. Leonard and S. K. Sleigh Phytochemistry 1978 17 899; A. H. Heckendorf and C. R. Hutchinson Tetrahedron Letters 1977,4153. 79 A. R. Battersby N. G. Lewis and J. M. Tippett Tetrahedron Letters 1978,4849. J. Stockigt H. P.Husson C. Kan-Fan and M. H. Zenk J.C.S. Chem. Comm. 1977 164. H. G. Floss,Tetrahedron 1976 32 873. D. J. Aberhart Tetrahedron 1977 33 1545. 83 H. Booth B. W. Bycroft C. M. Wels K. Corbett and A. P. Maloney J.C.S. Chem. Comm. 1976 110. 84 D. W. Young D. J. Morecombe and P.K. Sen European J. Biochem. 1977,75,133. J. A. Huddleston E. P.Abraham D. W. Young D. J. Morecombe and P.K. Sen Biochem. J. 1978 169,705. 86 G.W. Kirby G. L. Patrick and D. J. Robins J.C.S. Perkin I 1978 1336. 87 G. W. Kirby and D. J. Robins J.C.S. Chem. Comm. 1976 354. D. G. Buckley Ann. Reports (B) 1977 74 392. 89 A. I. Scott Accounts Chem. Res. 1978 11,29. 90 A. R.Battersby Experientia 1978 34 1. 91 A. R. Battersby C. J. R. Fookes E. McDonald and N. J. Meegan J.C.S. Chem. Comm. 1978,185;A. R.Battersby C. J. R. Fookes G. W. J. Matcham and E. McDonald ibid. p. 1064. Biological Chemistry deaminase :cosynthetase enzyme system ring-closes the unrearranged bilanes far more efficiently than any of the isomeric irregular bilanes. In support of its structure sirohydrochlorin is specifically incorporated into cobyrinic acid.92 The retention of 'sN-'3C coupling in streptonigrin (43) biosynthesized from [2-'3C,1-'5N]tryptophan has been used to show which bonds remain intact during the bio~ynthesis.~~'~~ C-Methylated amino-acids are quite rare.However /3-methyltryptophan has been shown" to be an intermediate in the biosynthesis of streptonigrin. A similar C-methylation occurs in the biosynthesis of indolmycin The use of methionine carrying a chiral methyl group has that this alkylation proceeds with inversion of configuration. The biosynthesis of the firefly luciferin (44) has been ~hown~'.~~ to involve the condensation between p-benzoquinone and two molecules of cysteine. 0 CH,O OCH (43) (44) 7 Miscellaneous Metabolites The conversion of octanoic acid to lipoic acid (45) involves the unusual substitution by sulphur at two saturated carbon atoms.This takes place without the loss of hydrogen from the adjacent centres (C-5 and C-7).99 A similar observation has been made on the incorporation of desthiobiotin into biotin."' s%,o OH (45) The labelling pattern of the antibiotics geldanamycin"' and pactamycin'02 by [6-'3C]glucose methionine and acetate has been described. 92 A. R. Battersby E. McDonald M. Thompson and V. Y. Bykhovsky J.C.S. Chem. Comm. 1978,150. 93 S. J. Gould and C. C. Chang J.Amer. Chem. SOC.,1978,100,1624. 94 S.J. Gould and C. C. Chang J. Amer. Chem. Sac. 1977,99 5496. 95 S. J. Gould and D. S. Darling Tetrahedron Letters 1978 3207. 96 L. Mascaro. R. Horhammer S. Eisenstein L. K. Sellers K. Mascaro and H. G. Floss.J. Amer. Chem. SOC.,1977,99,273.97 K. Okada H. Iio and T. Goto J.C.S. Chem. Comm. 1976 32. 98 F. McCapra and Z. Razavi J.C.S. Chem. Comm. 1976 153. 99 R. J. Parry J. Amer. Chem. SOC.,1977,99 6464. loo R. J. Parry and M. G. Kunitani J. Amer. Chem. SOC.,1976,98,4024. lo' A. Haber R. D. Johnson and K. L. Rinehart J. Amer. Chem. SOC.,1977,99 3541. D. D. Weller and K. L. Rinehart J. Amer. Chem. SOC., 1978 100 6757.