BIOSYNTHESIS OF ESPERAMICIN-A(1), AN ENEDIYNE ANTITUMOR ANTIBIOTIC

Biosynthetic studies on esperamicin Al (esp At) were carried out by ex amining the incorporation of singly and doubly C-13-labeled acetates, L-[methyl-C-13]methionine and (Na2SO4)-S-34, by cultures of Actinomadu ra verrucosospora MU-5019. The acetate incorporation results show that the C-15 bicyclic enediyne core of esp A1 is derived from head-to-tai l condensation of seven acetate units and the uncoupled carbon attache d to the trisulfide unit is derived from the C2 of acetate. The L-[met hyl-C-13]methionine incorporation result shows that the S-methyl group s of the trisulfide and the thiosugar and the O-methyl groups of the a minosugar, the aromatic chromophore, and the carbamate moiety are deri ved from L-methionine via S-adenosylmethionine. Using (Na2SO4)-S-34 as the sole sulfur source in the fermentation and by mass spectrometric analysis, we have demonstrated that all four sulfur atoms in esperamic in A1c (esp A1c) can be derived from (Na2SO4)-S-34. On the basis of th e C-13-labeled acetate-enrichment pattern, the enediyne ring moiety of esp A1 maybe derived from an octaketide with the loss of the Cl of th e end acetate unit. The acetate-enrichment pattern of the enediyne moi ety of esp A1 is in good agreement with that of dynemicin A (DNM-A). T he two carbons comprising the yne moieties of esp A1 and DNM-A are der ived from separate acetate units. The corresponding carbons in chromop hore A of neocarzinostatin (NCS Chrom A) are derived from the same ace tate units. This may suggest that enediyne cores of esp A1 and DNM-A a re biosynthesized from a common precursor while NCS Chrom A is biosynt hesized via a different process.