The Biosynthesis of Antibiotic F-244 in Fusarium sp. Atcc 20788

Abstract

<p>The naturally occurring antibiotic β-lactone F-244, also known as 1233A and L-659,699, is isolated from species of Fusarium, Scopulariopsis and Cephalosporium. This compound has been shown to be a potent specific inhibitor of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase, a key enzyme in the mammalian biosynthesis of cholesterol.</p> <p>Extensive multidimensional NMR analysis afforded unambiguous assignments of all the proton and carbon-13 resonances of F-244.</p> <p>The biosynthesis of F-244 in Fusarium sp. ATCC 20788 was investigated by incorporation of isotopically labelled precursors such as acetate and methionine into growing cultures. Separation and purification of the resulting labelled F-244 was followed by NMR analysis to determine the location of label.</p> <p>The results show that F-244 is a polyketide metabolite derived from 7 acetate units arranged in a typical "head-to-tail" fashion; the three methyl groups and the carbon of the hydroxymethyl moiety are derived from L-methionine. The carbonoxygen bonds at C₁₄=O and C₁₂-O are derived intact from acetate. These results define a probable sequence of events on the polyketide synthase surface, where acetate units are condensed and manipulated to give F-244.</p> <p>To test this hypothesis, several of the potential intermediates, both as free acids and as N-acetylcysteamine thioesters, with strategically placed deuterium or carbon-13 labels, were synthesized and fed to growing cultures of Fusarium sp. ATCC 20788.</p> <p>The results of feeding experiments using deuterium labelled putative intennediates showed that none of these precursors was incorporated intact. When the carbon-13 labelled intermediates were used, the ¹³C NMR spectra showed enhancements of the signals that are derived from C-1 of acetate, indicating that the labelled intermediates had been degraded by β-oxidation.</p> <p>[equations removed]</p>