Synthesis and Biological Activity of a New Type of PM-Toxin Analogue Containing Oxygen Atoms in the Carbon-Chain Skeleton

PM-toxins are host-specific pathotoxins produced by the corn fungal pathogen Phyllosticta maydis. Three PM-toxin analogues of a new type which have oxygen atoms in the skeletal carbon chain were synthesized as stereoisomeric mixtures. The linear ester PML-777 was about 100-times less active than the potent synthetic analogue PM-777 in an NADH oxidation assay using corn mitochondria. A large cyclic analogue, PMC 32 -7777, was only about 4- to 10-times less active than the parent linear ester PML-777, but over 500-times more active than a smaller sized analogue, PMC 20 - 711. The striking loss of biological activity in PML-777 clearly shows the significance of a carbon- chain skeleton like PM-777 for higher biological activity. The unexpectedly slight decrease of activity from PML-777 to PMC 32 -7777 may suggest that the active conformation of the linear analogue (PML-777) was similar to that of the cyclic analogue (PMC 32 -7777).