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

To clarify the biosynthetic origins of phytotoxin neovasinin 1 and its biogenetically related metabolites, neovasipyrones A 2 and B 3 and neovasifuranones A 6 and B 7, sodium [1,2-13C2]-, [1-13C]- and [2-13C]-acetate and L-[S-13CH3]methionine were fed to cultures of Neocosmospora vasinfecta NHL2298 in separate experiments. The labelling patterns of these metabolites indicated the same origin, viz. biosynthesis from a hexaketide chain plus five C1 units. The absolute stereochemistries of C-7 and C-8 in neovasifuranones A 6 and B 7 were established by chemical reactions, and the stereochemical relationships among the metabolites of the fungus supported the contention that the metabolites have the same biosynthetic origin. L-[S-13C2H3]Methionine was fed to the fungus to determine the oxidation level of the C1 units introduced during biosynthesis. The labelling patterns indicated 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.