Nucleophilic α-Functionalization of Benzyl Amines Using an Engineered Threonine Aldolase.

Chiral amines are ubiquitous in pharmaceuticals and agrochemicals, making their efficient and selective synthesis a significant synthetic challenge. Threonine aldolases synthesize chiral amines via stereoselective C-C bond formation; however, they are restricted to small amino acids as pro-nucleophiles, limiting their utility in chemical synthesis. Here, we report an engineered threonine aldolase capable of α-functionalizing benzylamines. The evolved enzyme has excellent catalytic efficiency and accepts a broad range of (heterocyclic)benzyl amines and structurally diverse aldehydes to yield single-enantiomers of 1,2-amino alcohols in high-yield and diastereoselectivity. Mechanistic and crystallographic studies provide a rationale for how these mutations enable this previously unknown function. Moreover, beneficial mutations can be transferred to a related pyridoxal-dependent protein, highlighting the generality of these insights.