Absolute stereochemistry of spiciferones and spicifernin, bioactive metabolites of the fungus Cochliobolus spicifer: evidence for their unique biosynthesis

Abstract

The absolute stereochemistry of spiciferone A and spicifernin, a phytotoxin and a plant-growth promoter, respectively, produced by the phytopathogenic fungus Cochllobolus spicifer Nelson, has been determined by the application of Masher's method after establishment of relative stereochemistry by X-ray analysis. The absolute stereochemistry of spiciferones B and C has been determined by CD spectral comparison. Their absolute stereochemistry was in good agreement with the proposed polyketide biosynthetic pathway in which spiciferones and spicifernin are formed from a common cyclic precursor by a sequence of biological reactions involving a unique retro-aldol condensation.