Structures of AM-toxin I and II, host specific phytotoxic metabolites produced by Alternaria mali.

Abstract

Two host specific phytotoxic metabolites, AM-toxin I and II, were isolated from culture broth and mycelial mat of Alternaria mali, the fungus causing leaf-spot disease of apple. Chemical and spectral data showed AM-toxin I to be a cyclic depsipeptide consisting of each one molecule of the following four components; L-α-hydroxy-isovaleric acid, L-alanine, α-amino acrylic acid, and L-α-amino-δ-(p-methoxyphenyl)-valeric acid. Their sequence in the molecule of AM-toxin I was decided as shown in (IIa). The structure of AM-toxin II was also assigned to (IIb) from the correlation of its spectral data with those of AM-toxin I.