Transaminase Engineering and Process Development for a Whole-Cell Neat Organic Process to Produce (R)-α-Phenylethylamine

The production of ( R )-α-phenylethylamine (( R )-α-PEA) from acetophenone is a classic reaction for the characterization of transaminases. However, developing a commercially viable transaminase process to manufacture ( R )-α-PEA usually suffers from two drawbacks. One is related to the biocatalyst itself, since transaminases are easily inhibited by ( R )-α-PEA at low concentrations. The other drawback is a common low space-time yield of typical transaminase processes, because the reaction equilibrium greatly favors the formation of acetophenone over ( R )-α-PEA. In this study, an ( R )-selective amine transaminase (TA) from Aspergillus fumigatus Af293 was engineered by a directed evolution for an efficient process to produce ( R )-α-PEA. The evolved variant showed an over 3000-fold increase in activity and a tolerance with 2.0 M isopropylamine as well as the complete absence of inhibition by ( R )-α-PEA. At the same time, using this evolved TA variant, a continuous neat organic process using whole-cells was developed where the biocatalyst and remaining acetophenone can be efficiently separated from ( R )-α-PEA and reused repetitively. This not only decreases the overall cost and waste generation but also achieves a very high space-time yield of up to 168 g L –1 d –1 of ( R )-α-PEA in an industrial pilot scale setup.