Ralfuranone Is Produced by an Alternative Aryl-Substituted γ-Lactone Biosynthetic Route in Ralstonia solanacearum

The aryl-substituted γ-lactones ralfuranones A and B were isolated after feeding l-[1-13C]-phenylalanine to a liquid culture of the plant pathogenic bacterium Ralstonia solanacearum. 13C NMR analysis demonstrated specific enrichment of the label at position 2 of the γ-lactone. This labeling pattern is consistent with a biosynthetic mechanism that includes direct cyclization of two monomeric phenylpyruvate precursors into an α,β-substituted lactone, but incompatible with a terphenylquinone intermediate. As the latter was shown as an intermediate in allantofuranone biosynthesis, we conclude that aryl-substituted γ-lactones can be assembled via divergent biosynthetic routes.