Reaction Optimization by a Lysine Amine Donor. (2S,3S)-alkyl substituted arylalanines are critical -branched ncAAs in ongoing peptide drug discovery efforts, but their chemical synthesis via cross-electrophile coupling requires Scheme 1. Transaminases in chiral amine synthesis protecting groups and a challenging separation of -stereoisomers. For a sustainable and more efficient route to these compounds, we reasoned that a transaminase could generate the desired ncAA in high enantioselectivity from the corresponding keto acid and an appropriate amine donor. Furthermore, if the keto acid substrate's -stereocenter racemizes under sufficiently alkaline conditions, we could leverage high enzyme substrate specificity in a DKR from a readily prepared racemate. For our initial studies, we chose the transformation of 3-(naphthalen-1-yl)-2-oxobutanoic acid (2) to (2S,3S)-2-amino-3-(naphthalen-1-yl)butanoic acid (3).