Precursor directed biosynthesis of aureobasidins.

The antifungal antibiotic aureobasidin A (AbA) is a cyclic depsipeptide composed of eight amino acids and a hydroxy acid. New Ab analogs were produced by feeding various amino acids to Aureobasidium pullulans R 106 c-712 in a chemically-defined medium containing glucose and ammonium sulfate. The constituent amino acids of AbA at positions 3 (L-phenylalanine), 4 (N-methyl-L-phenylalanine), 5 (L-proline), 6 (L-allo-isoleucine) and 8 (L-leucine) were replaced by respective analogous amino acids such as o-fluoro-L-phenylalanine, 4-hydroxy-L-proline, L-norleucine and L-norvaline, resulting in the production of eight new Ab analogs. This is the first paper to describe amino acid replacements at positions 3, 5 and 8. L-[1-13C]-Valine exogenously added was incorporated into the three valine-related moieties of AbA at positions 2, 7 (both N-methyl-L-valine) and 9 (beta-hydroxy-N-methyl-L-valine), but these moieties were never replaced by exogenous amino acid analogs. The comparative antifungal activities of AbA and the eight new Ab analogs were determined.