Asymmetric C1 Extension of Aldehydes through Biocatalytic Cascades for Stereodivergent Synthesis of Mandelic Acids

The development of mild, efficient, and enantioselective methods for preparing chiral building blocks from simple, renewable carbon units has been a long-term goal of the sustainable chemical industry. Mandelate derivatives are valuable pharmaceutical intermediates and chiral resolving agents, but their manufacture relies heavily on highly toxic cyanide. Herein, we report (S)-4-hydroxymandelate synthase (HmaS)-centered biocatalytic cascades for the synthesis of mandelates from benzaldehydes and glycine. We show that HmaS can be engineered to perform (R)-selective hydroxylation by single-point mutation, empowering the stereo-divergent synthesis of both (S)- and (R)-mandelate derivatives. We demonstrated that these biocatalytic cascades enabled the production of various mandelate derivatives with great atom economy, excellent yields (up to 98%) and enantiomeric excess (up to >99%). This methodology offers an effective cyanide-free technology for greener and sustainable production of mandelate derivatives.