Biosynthesis of phytotoxin neovasinin and its related metabolites, neovasipyrones A and B and neovasifuranones A and B, in the phytopathogenic fungusNeocosmospora vasinfecta

To clarify the biosynthetic origins of phytotoxin neovasinin 1 and its biog enetically related metabolites, neovasipyrones A 2 and B 3 and neovasifuran ones A 6 and B 7, sodium [1,2-C-13(2)]-, [1-C-13]- and [2-C-13]-acetate and L-[S-(CH3)-C-13]methionine were fed to cultures of Neocosmospora vasinfect a NHL2298 in separate experiments. The labelling patterns of these metaboli tes indicated the same origin, viz. biosynthesis from a hexaketide chain pl us five C-1 units. The absolute stereochemistries of C-7and C-8 in neovasif uranones A 6 and B 7 were established by chemical reactions, and the stereo chemical relationships among the metabolites of the fungus supported the co ntention that the metabolites have the same biosynthetic origin. L-[S-(CH3) -C-13-H-2]Methionine was fed to the fungus to determine the oxidation level of the C-1 units introduced during biosynthesis. The labelling patterns in dicated that in their biosynthesis the common intermediates are aldehydic, not alcoholic, compounds. The conversion of neovasifuranone A aldehyde 9 to neovasifuranone A 6 in vivo and in vitro is also evidence of this.