Amine Transaminase Engineering for Spatially Bulky Substrate Acceptance

Amine transaminase (ATA) catalyzing stereoselective amination of prochiral ketones is an attractive alternative to transition metal catalysis. As wild‐type ATAs do not accept sterically hindered ketones, efforts to widen the substrate scope to more challenging targets are of general interest. We recently designed ATAs to accept aromatic and thus planar bulky amines, with a sequence‐based motif that supports the identification of novel enzymes. However, these variants were not active against 2,2‐dimethyl‐1‐phenyl‐propan‐1‐one, which carries a bulky tert‐butyl substituent adjacent to the carbonyl function. Here, we report a solution for this type of substrate. The evolved ATAs perform asymmetric synthesis of the respective R amine with high conversions by using either alanine or isopropylamine as amine donor. An amine transaminase was evolved to accept bulky 2,2‐dimethyl‐1‐phenyl‐propan‐1‐one, which carries a tert‐butyl substituent adjacent to the carbonyl function. The evolved ATAs are able to perform asymmetric synthesis of the respective (R)‐amine at high conversion and with excellent stereoselectivity with either alanine or isopropylamine as donor.