Unifying Scheme for the Biosynthesis of Acyl-Branched Sugars: Extended Substrate Scope of Thiamine-Dependent Enzymes

Thiamine diphosphate (ThDP) dependent enzymes are useful catalysts for asymmetric C−C bond formation through benzoin‐type condensation reactions that result in α‐hydroxy ketones. A wide range of aldehydes and ketones can be used as acceptor substrates; however, the donor substrate range is mostly limited to achiral α‐keto acids and simple aldehydes. By using a unifying retro‐biosynthetic approach towards acyl‐branched sugars, we identified a subclass of (myco)bacterial ThDP‐dependent enzymes with a greatly extended donor substrate range, namely functionalized chiral α‐keto acids with a chain length from C₄ to C₈. Highly enantioenriched acyloin products were obtained in good to high yields and several reactions were performed on a preparative scale. The newly introduced functionalized α‐keto acids, accessible by known aldolase‐catalyzed transformations, substantially broaden the donor substrate range of ThDP‐dependent enzymes, thus enabling a more general use of these already valuable catalysts.