On the Biosynthetic Origin of Methoxymalonyl-Acyl Carrier Protein, the Substrate for Incorporation of ‘Glycolate’ Units into Ansamitocin and Soraphen A.

Feeding experiments with isotope-labeled precursors rule out hydroxypyruvate and TCA cycle intermediates as the metabolic source of methoxymalonyl-ACP, the substrate for incorporation of ‘glycolate’ units into ansamitocin P-3, soraphen A, and other antibiotics. They point to 1,3-bisphosphoglycerate as the source of the methoxymalonyl moiety and show that its C-1 gives rise to the thioester carbonyl group (and hence C-1 of the ‘glycolate’ unit), and its C-3 becomes the free carboxyl group of methoxymalonyl-ACP, which is lost in the subsequent Claisen condensation on the type I modular polyketide synthases (PKS). ᴅ-[1,2-13C2]Glycerate is also incorporated specifically into the ‘glycolate’ units of soraphen A, but not of ansamitocin P-3, suggesting differences in the ability of the producing organisms to activate glycerate. A biosynthetic pathway from 1,3-bisphosphoglycerate to methoxymalonyl-ACP is proposed. Two new syntheses of R- and S-[1,2-13C2]glycerol were developed as part of this work. [ABSTRACT FROM AUTHOR]