Further studies on the biosynthesis of the avermectins

Abstract

The biosynthesis of avermectins was studied further in Streptomyces avermitilis MA5502 by feeding experiments with labeled precursors. 13C-NMR analysis of the compounds biosynthesized from [2-13C]acetate, [1,2-i3C2]acetate, [3-z3C]propionate and [2,3-13C2]propionate confirmed that the aglycone of avermectins is made from seven intact acetate and five propionate units. Feeding experiments with [1-13C]2-methylbutyrate and [1-13C]isobutyrate have shown that 2-methylbutyrate and isobutyrate are immediate precursors of the starter units of the polyketide chains of avermectin 'a' and 'b' components, respectively. The 3H/~4C doublelabeling experiments suggest that the two oleandrose moieties are derived from glucose.