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

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. magnified image 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.