Synthesis and biological activity of mimics of PM-toxins, the host-specific corn pathotoxin produced by Phyllosticta maydis

To establish structure-activity relationships, 12 mimics of PM-toxin A, a component of the host-specific corn pathotoxin produced by Phyllosticta maydis, have been synthesized as stereoisomeric mixtures. All the mimics synthesized have four beta -ketol groups spaced by varying lengths of methylene chains or by a 1,3-diene chain. Mimics with the shorter methylene side-spacers or with the diene side-spacers are 30- to 300-fold less toxic than the native toxin, but the remaining compounds are equally or more toxic than the native toxin. These results can be accounted for by postulating that intramolecular associations at the beta -ketol groups may yield two types of cage structure with active and less active conformations. (DBO)