Buffer-Mediated Catalyst-Free Strecker Reaction Toward Enzymatic Implementation

A systematic investigation of the catalyst-free Strecker reaction is conducted in aqueous buffer, offering an efficient and green alternative that leads to α-aminonitriles without the need of chromatography. Optimization reveals that low pH and high buffer concentration significantly enhance conversion, with yields up to 97%. Broad substrate scope is demonstrated with various aldehydes, ketones, and amines, leading to key intermediates for natural and unnatural amino acids. Potassium cyanide and acetone cyanohydrin are established, latter as a safer and effective cyanide source, and reactions are conducted also in buffer-methyl tert-butyl ether mixed solvent further improving the methodology. It is hypothesized that, based on the similarity to cyanohydrin formation, the hydroxynitrile lyases (HNLs) might transform imines to aminonitriles. Adding AtHNL and HbHNL further accelerates the reaction suggesting an undiscovered reactivity of these enzymes.