Natural enniatin A, a mixture of optical isomers containing both erythro-and threo-N-methyl-L-isoleucine residues

Abstract

Chromatography of a mixture of enniatins from Fusarium sambucinum Fuckel yielded a major fraction with the physical properties of synthetic enniatin A. The only amino-acid released by hydrolysis was N-methylisoleucine, as a mixture of erythro-L and threo-L epimers whose ratio showed enniatin A to consist of at least two isomers. Hydrolysis of enniatin in mixed hydrochloric and acetic acids gave completely racemized 2-hydroxyisovaleric acid. The o.r.d. spectra of D-2-hydroxyisovaleric acid and of N-methyl-erythro-L- and threo-D-isoleucines are recorded.