Date of Award

5-1995

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Supervisor

P. Harrison

Abstract

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.

Extensive multidimensional NMR analysis afforded unambiguous assignments of all the proton and carbon-13 resonances of F-244.

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.

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.

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.

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.

[equations removed]

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