Enzyme-Catalyzed Intramolecular C-C Coupling Transformation of Nitriles

Nitrile C-C coupling transformation, currently absent from existing biocatalytic toolbox, is a pivotal objective in enzyme catalysis. Herein, we engineered a ThDP-dependent enzyme to achieve nitrile C-C coupling with in situ-generated acyl anion equivalent, providing a valuable synthetic complement to current enzymatic transformations. This reaction also constitutes the first ThDP-dependent enzymatic addition of aldehyde group to an inert triple bond. Under mildly acidic aqueous conditions, this biocatalytic reaction achieves effective hydrolysis of readily isomerizable imine intermediates. Such a hydrolysis process poses formidable challenges to organic solvent-reliant chemical reactions and has been scarcely explored. In addition, this reaction constitutes an enzyme-catalyzed, oxidant-free strategy for the efficient synthesis of valuable 3-hydroxychromones─key intermediates for accessing flavonol natural products and functional molecules. Related mechanistic studies and preliminary kinetic resolution experiments were also conducted. Our study will encourage further development of biocatalytic systems for nitrile C-C coupling transformations, particularly those challenging to chemical methods.