Gliotoxins, biosynthesis

Cyclo(L-[U- C]phenylalanyl-L-phenylalanine) is incorporated into BDA in 19.9% yield, in cultivation for 48 hr in Asp. terreus (141). In contrast, the cyclo L,D and D,D isomers are not incorporated. Further, the isolation of cis-3,6-bibenzyl-3,6-bis(methylthio)piperazine-2,5-dione (71), mp 291-293°C, [a]54g — 122°, from Asp. terreus (142) suggests that the sulfur atoms are introduced in an early stage of aranotin biosynthesis, as in gliotoxin biosynthesis. 

Gliotoxin.—cyc/o-(L-Phenylalanyl-L-seryl) (121) has been observed to be an intact and efficient precursor for gliotoxin (122) in Trichoderma viride. This has been confirmed in further experiments with (121) and its three stereoisomers. Only (121) was incorporated at all efficiently (at least forty times better than the others) it was also proved to be utilized intact. Moreover, (121) was formed from labelled phenylalanine in growing cultures. It follows that (121) is either an intermediate in gliotoxin biosynthesis, or is reversibly converted into an intermediate on the pathway. The biosynthesis of gliotoxin has been reviewed. 

Further proof that all nine carbon atoms of phenylalanine, and not merely the aliphatic side chain, were incorporated into gliotoxin was provided by the isolation of gliotoxin- H after phenylalanine-U- H was added to growing cultures of r. viride. Seventeen percent of the administered tritium-labeled phenylalanine was incorporated into gliotoxin (Winstead and Suhadolnik, I960). These results therefore establish the aromatic amino acid pathway and not the acetate pathway as operative in gliotoxin biosynthesis by T. viride. 

If the analogy with gliotoxin biosynthesis is extended, c7cto(L-phenylalanyl-L-phenylalanyl) should be a precursor for all members of the aranotin group, but, so far, this point has not been tested experimentally. 

The metabolic steps leading from tryptophan to sporidesmin have not been investigated in any detail, although one might expect a close correspondence with gliotoxin biosynthesis. For example, formation of the fused pyrrolidine system could involve an intermediate epoxide (26) analogous to... 

Arene oxides and their oxepin tautomers play a role in the biosynthesis of some microbial metabolites, e.g., the sulfur-containing antibiotics gliotoxin (345),188 dehydrogliotoxin (346),189 apoarontin (347),190 aranotin (348),191... 

Gliotoxin.—Examination of the biosynthesis of gliotoxin (148) in Gliocladium deliquescens has shown that a new metabolite (149) is formed, apparently irreversibly, from (148).62... 

The mechanism of entry of sulphur in gliotoxin formation is an intriguing puzzle. A route involving a ATV-dihydroxy-diketopiperazine (146) derived from (145) cf. Vol. 10, p. 27), followed by (147), is lent support by the results of chemical experiments.63 By contrast, ring-closure involving sulphur in the biosynthesis of penicillins is likely to involve a radical mechanism.64... 

Aranotins and Sirodesmin.—ctc/o-(l Phenylalanyl-L-seryl) is an efficient and intact precursor for gliotoxin (114) (cf. Vol. 10, p. 27). Bisdethiobis(methylthio)-acetylaranotin (115) is related to gliotoxin in the biosynthesis of this metabolite, it is believed that ring-opening of an arene oxide las (116)1 occurs, followed by further epoxidation and cyclization, as in the biosynthesis of gliotoxin (114).2... 

Organic Syntheses and Organic Reactions, Jack and his students published research papers on organo-boron compounds, furan derivatives, dienes, ketene derivatives, the structure of gliotoxin, and biosynthesis of isoprene derivatives. 

Intramolecular nucleophilic attack of an amine group on an arene oxide has been proposed to account for the biosynthesis of a range of epipolythiopiperazine-diones (e.g., gliotoxin, bis-dithiobis-(methylthio)dehydrogliotoxin, spirodesmins, etc.)- With the amine-substituted arene oxides 50 and 55 (Figure 3), synthe-... 

Further investigation of the biosynthesis of gliotoxin has shown that although cyc/o-L-phenylalanyl-L-seryl (157) was apparently able to permeate the mycelium of Penicillium terlikowskii, it was not incorporated into gliotoxin (156) under conditions when phenylalanine was. Similar negative results were obtained for mycelianamide (158) in P. patulum with cycto-L-alanyl-L-tyrosyl (159) and cyc/o-L-alanyl-D-tyrosyl which were also able to permeate the mycelium. In contrast [l- CJtyrosine was specifically incorporated with high efficiency (there was no significant difference in the efficiency with which the d- and L-isomers of tyrosine were utilized). 

The chemistry of gliotoxin was extensively studied by Johnson and co-workers 115,117). The correct structure was finally proposed in 1958 and confirmed by X-ray analysis (1966) 118) which also revealed the absolute configuration. Many reviews have been published on the structure, chemistry, biosynthesis, and biological activity of gliotoxin 119-123). A total synthesis of gliotoxin, using the Michael reaction as a key step, was achieved by Kishi and co-workers 124) (Scheme 11). 

A number of microbial metabolites whose biosynthesis has been studied are (at least formally) derived from a di- (or tri-)peptide echinulin and benzodiazepine alkaloids (both referred to already), gliotoxin, mycelianamide/ sporidesmin, and the /3-lactam antibiotics. In the case of the last mentioned, in spite of extensive work and the accumulation of a wealth of detail on the fates of the individual atoms in the precursor amino-acids, the mechanism of ring formation remains obscure. 

Herscheid JDM, Nivard RJF, Tijhuis MW, Otfimheijm HCJ (1980) Biosynthesis of Gliotoxin. Synthesis of Sulfur-Bridged Dioxopiperazines liom JV-Hydroxyamino Acids. J Org Chem 45 1885... 

The biosynthesis pathway of both gliotoxin and sirodesmin PL starts with a condensation reaction of two amino acids catalyzed by an NRPS enzyme. In particular, phenylalanine and serine condensations are catalyzed by a dioxopiperazine synthase, GliP, for gliotoxin, while DMAPP, tyrosine, and serine condensation are catalyzed by a dimethylallyl synthase, SirD, and a dioxopiperazine synthase, SirP, for sirodesmin (Figure 6.74). 

Gliotoxin is a representative of a group of diketopiperazine-derived fungal toxins. It is formed from L-tryptophan and L-serine. A key intermediate is the cyclic dipeptide of these two amino acids (Fig. 334). The biosynthesis of the cyclo-hexadienol ring probably involves an epoxy intermediate. The incorporated sulfur may come from L-cysteine. 

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