Oxalyl‐CoA Decarboxylase Enables Nucleophilic One‐Carbon Extension of Aldehydes to Chiral α‐Hydroxy Acids

The synthesis of complex molecules from simple, renewable carbon units is the goal of a sustainable economy. Here we explored the biocatalytic potential of the thiamine‐diphosphate‐dependent (ThDP) oxalyl‐CoA decarboxylase (OXC)/2‐hydroxyacyl‐CoA lyase (HACL) superfamily that naturally catalyzes the shortening of acyl‐CoA thioester substrates through the release of the C(1)‐unit formyl‐CoA. We show that the OXC/HACL superfamily contains promiscuous members that can be reversed to perform nucleophilic C(1)‐extensions of various aldehydes to yield the corresponding 2‐hydroxyacyl‐CoA thioesters. We improved the catalytic properties of Methylorubrum extorquens OXC by rational enzyme engineering and combined it with two newly described enzymes—a specific oxalyl‐CoA synthetase and a 2‐hydroxyacyl‐CoA thioesterase. This enzymatic cascade enabled continuous conversion of oxalate and aromatic aldehydes into valuable (S)‐α‐hydroxy acids with enantiomeric excess up to 99 %.