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

Abstract

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.