BIOSYNTHESIS OF THE ZARAGOZIC ACIDS .1. ZARAGOZIC ACID-A

The biosynthetic precursors of zaragozic acid A, a member of a new class of squalene synthase inhibitors, were determined. Washed cells of the producing culture, an unidentified sterile fungus, were supplemented with both C-14- and C-13-labeled substrates, and isolated zaragozic acid A was analyzed by scintillation counting and carbon NMR analysis, respectively. Zaragozic acid A is derived from two polyketide chains. Chain A begins with an aromatic ring derived from benzoic acid, itself derived from metabolism of phenylalanine, and continues in a polyketide fashion by condensation of five acetate units. The terminal four carbon atoms of chain A appear to arise from condensation of succinic acid to the polyketide chain, although citric acid cannot be ruled out as a source of the terminal six carbons. The acetyl group at C-4' arises from acetate, and the final two carbons of chain A arise by C-methylation from the methyl Of L-methionine to give the methylene at C-3' and the methyl at C-5'. Chain B is a polyketide formed by condensation of four acetate units and two C-methylations from L-methionine to give the two branched methyl groups at C-4'' and C-6''. Proposals for the biosynthesis of related products zaragozic acids B and C are presented.