Solanapyrones, Phytotoxins Produced by Alternaria solani: Biosynthesis and Isolation of Minor Components.

Two minor components of solanapyrones D and E, phytotoxins from Alternaria solani, were isolated. The absolute stereochemistry of D and the optical purity of solanapyrones A and D were determined by chemical transformation and measurement of the CD spectrum. In addition, complete signal assignment of the (1)H- and (13)C-NMR spectra of solanapyrones A and D, and their solution conformations were studied. Feeding experiments with various isotopically labeled acetates and methionine established the biosynthetic pathway of solanapyrones. The phytotoxicity of solanapyrones on lettuce seedlings is discussed.