“…Noncanonical amino acids, which are not naturally encoded into proteins, have unusual biological activities in their optically pure form and are important building blocks of agrochemicals and pharmaceuticals. − For example, l -phosphinothricin is a promising herbicide; l - tert -leucine, l -homoalanine, and l -phenylglycine are used to synthesize the anti-AIDS drug atazanavir, the anti-epileptic levetiracetam, and the antibiotic clopidogrel, respectively; − l -norvaline and l -homophenylalanine are the building blocks for angiotensin converting enzyme (ACE) inhibitors, such as perindopril, benazepril, captopril, enalapril, lisinopril, and quinapril. − Biocatalytic synthesis of these chiral amino acids with high optical purity is a reliable, scalable, and preferred route owing to its remarkable chemo-, regio-, and stereoselectivity features, coupled with safety and environmental benefits. , Among them, the asymmetric reductive amination of prochiral keto acids catalyzed by amino acid dehydrogenase (AADH) is a very efficient strategy for the production of noncanonical chiral amino acids, − with advantages like direct use of cheap ammonia as the amino donor, high atom utilization, and high optical purity of the products (often exceeding 99%). However, though numerous AADHs have been identified and classified according to their substrate specificities, such as glutamate dehydrogenase (GluDH), leucine dehydrogenase (LeuDH), and phenylalanine dehydrogenase (PheDH), only a few AADHs have considerable potential as biocatalysts for the reductive amination processes .…”