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 chi- ral 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 crystallo- graphic 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, high- lighting the generality of these insights.