Antifungal cyclodepsipeptides, W493 A and B, from Fusarium sp.:: Isolation and structural determimation

W493 A and B, which showed strong antifungal activity, were isolated from a culture broth of Fusarium sp. The structure of W493 B was determined to be that of a cycle clodepsipeptide, cycle(3S,4R-HMTA-D-allo-Thr-L-Ala-DAla-L-Gln-D-Tyr-L-Ile) (1) by MS and NMR data, an amino acid analysis, and synthesis of the component. HMTA represents 3-hydroxy-4-methyltetradecanoic acid. W493 A (2) had a similar structure, except that L-ne in 1 was replaced by L-Val. The absolute configuration of each amino acid was determined by chiral HPLC, and the sequence of the components was determined by HMBC experiments. The sequence of the two alanines was determined to be a L-Ala-D-Ala by a chiral HPLC analysis of the peptide fragment containing only one Ala residue. The absolute configuration of HMTA obtained from the hydrolysis of W493 B was determined to be 3S and 4R by comparing with four isomers prepared by enantioselective synthesis via Sharpless asymmetric epoxidation.