The chemistry of pseudomonic acid. Part 1. The absolute configuration of pseudomonic acid A

Abstract

The configuration of the double bond in pseudomonic acid A (1a) is shown to be E by comparison of the spectroscopic properties of its methyl ester (1b) with those of methyl isopseudomonate A (2) obtained from (1b) by photolysis. Ozonolysis of methyl pseudomonate A (1b) afforded the crystalline ketone (3a). An X-ray analysis of the o-bromophenylhydrazone derivative of ketone (3a) confirmed the structural assignment and provided the absolute stereochemistry at each of the eight chiral centres. Pseudomonic acid A, therefore, may be formulated as (4), 9-{4-[5S-(2S,3S-epoxy-5S-hydroxy-4S-methylhexyl)-3R,4R-dihydroxytetrahydropyran-2S-yl]-3-methylbut-2(E)-enoyloxy}nonanoic acid.