Dynamic Kinetic Resolution of α‐Aminonitriles to Form Chiral α‐Amino Acids

Abstract

Abstract We have succeeded in the enzymatic synthesis of ( R )‐α‐aminobutyric acid from racemic α‐aminobutyronitrile. This has been demonstrated by the use of non‐stereoselective nitrile hydratase (NHase) from Rhodococcus opacus 71D, D ‐aminopeptidase from Ochrobactrum anthropi C1‐38 and α‐amino‐ε‐caprolactam (ACL) racemase from Achromobacter obae . Racemic α‐aminobutyronitrile was completely converted in 6 h at 30 °C to ( R )‐α‐aminobutyric acid whose optical purity was more than 99%. ( S )‐α‐Aminobutyric acid was also synthesized from α‐aminobutyronitrile by NHase, ACL racemase and L ‐amino acid amidase from Brevundimonas diminuta TPU 5720. In a similar manner, other ( R )‐ or ( S )‐α‐amino acids with more than 97.5% ee could be synthesized from the corresponding α‐aminonitriles. This is the first report on the dynamic kinetic resolution (DKR) of α‐aminonitriles to form chiral α‐amino acids. The key enzyme in this DKR is non‐stereoselective NHase, which had been newly screened from soil samples, and its gene cloned.