Alternaric acid. Proof of biosynthesis via condensation of two polyketide chains. Complete assignment of the 1H and 13C magnetic resonance spectra by 2D techniques

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Abstract
Incorporation studies utilizing [1,2-13C2]acetate have established that the fungal phytotoxin alternaric acid is biosynthesized by an uncommon condensation of two polyketide chains rather than from a single chain undergoing an a priori possible, albeit improbable, rearrangement. Unequivocal assignments for the 13Cmr spectra followed from the results of three 2D experiments, namely, homonuclear (1H) and heteronuclear (1H, 13C) correlation spectra and double quantum coherence (13C). Attempts to distinguish between the two possible loci of the chain junction were unsuccessful, suggesting that the synthesis may proceed on a single enzyme complex, without intervention of discrete intermediates.