Malonyl carba(dethia)- and Malonyl oxa(dethia)-coenzyme A as Tools for Trapping Polyketide Intermediates

Abstract

Caught in a trap. In this study trapped polyketide species (see figure) were off-loaded from a type III PKS by novel nonhydrolyzable malonyl coenzyme A analogues in which a methylene group or an oxygen atom replaces the sulfur atom of malonyl-CoA. This strategy allows the straightforward characterisation of intermediates of polyketide biosynthesis by LC-HR-ESI-MS/MS and provides valuable insights on the mechanism and timing of polyketide formation.In order to study intermediates in polyketide biosynthesis two nonhydrolyzable malonyl coenzyme A analogues were synthesised by a chemoenzymatic route. In these analogues the sulfur atom of CoA was replaced either by a methylene group (carbadethia analogue) or by an oxygen atom (oxadethia analogue). These malonyl-CoA analogues were found to compete with the natural extender unit malonyl-CoA and to trap intermediates from stilbene synthase, a type III polyketide synthase (PKS). From the reaction of stilbene synthase with its natural phenylpropanoid substrates, diketide, triketide and tetraketide species were successfully off-loaded and characterised by LC-MS. Moreover, the reactivity of the nonhydrolyzable analogues offers insights into the flexibility of substrate alignment in the PKS active site for efficient malonyl decarboxylation and condensation.