Processes using amino acid dehydrogenases and ketoreductase-based cofactor regenerating system

A process for converting a compound of formula I which is a substrate for an amino acid dehydrogenase to a chiral amino acid of formula IIa:

• comprising contacting the compound of formula I with a reaction medium comprising an amino acid dehydrogenase, an ammonium ion donor selected from ammonia or an ammonium salt, a cofactor selected from NAD+/NADH or NADP+/NADPH, and a cofactor regenerating system comprising an engineered ketoreductase encoded by an engineered polynucleotide having at least 90% sequence identity to SEQ ID NO:
• 17, which has less than 5% of the activity of an amino acid dehydrogenase, with compound of formula I and a lower secondary alcohol, under conditions where the compound of formula I is converted to the chiral amino acid of formula IIa and the lower secondary alcohol is converted to a ketone, and wherein R is a substituted or unsubstituted —(C1-C10)alkyl, —(C2-C6)alkenyl, —(C2-C6)alkynyl, —(C3-C8)cycloalkyl, heterocycloalkyl, aryl, or heteroaryl.