Exemplifying Natural (R)-β-Transamination Potential of Fold Type-IV Transaminase for Kinetic Resolution of rac-β-Amino Acids Synthesized from Aldehydes

Abstract

Sustainable synthesis of chiral β-amino acids from renewable feedstocks is of significant importance. The Rodionov reaction is a popular method to synthesize rac-β-amino acids from aldehydes, which are abundant byproducts of biomass. rac-β-Amino acids are easily converted into the enantiopure (R)-form by kinetic resolution using (S)-β-transaminases (TAs). However, the inaccessibility of natural (R)-β-transaminases with a broader substrate scope limits the application of the Rodionov reaction to produce (S)-β-amino acids. Here, we report the kinetic resolution of rac-β-amino acids by employing fold type-IV transaminase from Thermobaculum terrenum (TATT) with natural (R)-β-transaminase activity. Various rac-β-amino acids were successfully resolved by TATT into (S)-form with excellent conversions (∼50%) and enantiomeric excess (>99%) using pyruvate as an amino acceptor. The directed evolution of TATT resulted in a variant M-58 (K112F/F114M) with ∼2-fold higher activity and was able to perform large-scale kinetic resolution of 20 mM rac-3-amino-3-(3-fluorophenyl) propanoic acid (1h) with complete conversion and enantiomeric excess >99% within 24 h.