Isolation and Structures of AK-Toxin I and II, Host-specific Phytotoxic Metabolites Produced by Alternaria alternata Japanese Pear Pathotype

Abstract

Two host-specific phytotoxic metabolites, AK-toxin I and II, were isolated from a culture broth of Alternaria alternata Japanese pear pathotype, the fungus causing black spot disease of susceptible Japanese pear cultivars. From chemical, spectral and X-ray crystallographic data, AK-toxin I was characterized as 8-[(2'S, 3'S)-2'-acetylamino-3'-methyl-3'-phenyl-propionyloxy](8R, 9S)-9, 10-epoxy-9-methyl-deca-(2E, 4Z, 6E)-trienoic acid. The structure of AK-toxin II was also assigned to be 3'-demethyl derivative of AK-toxin I by comparing the spectral data with those of AK-toxin I.