Chiral Betaine-Catalyzed Biomimetic Transamination of α-Keto Esters

Enzymatic transamination is a highly efficient process for the biosynthesis of chiral α-amino acids. Here we report a chiral betaine-K₂CO₃ catalyst system that promotes the asymmetric transamination of α-keto esters for the asymmetric synthesis of chiral α-amino esters. It is noteworthy that this catalyst system achieved excellent enantioselectivity across a broad range of substrates with 0.025-0.2 mol % catalyst. Based on computational studies and control experiments, we propose a mechanism involving K₂CO₃-mediated deprotonation followed by a chiral betaine-mediated protonation to provide a rationale for the proton transfer catalysis of the current asymmetric transamination.