One-Pot Preparation of d-Amino Acids Through Biocatalytic Deracemization Using Alanine Dehydrogenase and ω-Transaminase

d-Amino acids are pharmaceutically important building blocks, leading to a great deal of research efforts to develop cost-effective synthetic methods. Preparation of d-amino acids by deracemization has been conceptually attractive owing to facile synthesis of racemic amino acids by Strecker synthesis. Here, we demonstrated biocatalytic deracemization of aliphatic amino acids into d-enantiomers by running cascade reactions; (1) stereoinversion of l-amino acid to a d-form by amino acid dehydrogenase and ω-transaminase and (2) regeneration of NAD⁺ by NADH oxidase. Under the cascade reaction conditions containing 100 mM isopropylamine and 1 mM NAD⁺, complete deracemization of 100 mM dl-alanine was achieved after 24 h with 95% reaction yield of d-alanine (> 99% ee^D, 52% isolation yield). Graphical Abstract: [Figure not available: see fulltext.].