Continuous Flow Synthesis of Chiral Amines in Organic Solvents: Immobilization of E. coli Cells Containing Both ω-Transaminase and PLP

E. coli cells containing overexpressed (R)-selective ω-transaminase and the cofactor PLP were immobilized on methacrylate beads suitable for continuous flow applications. The use of an organic solvent suppresses leaching of PLP from the cells; no additional cofactor was required after setting up the packed-bed reactor containing the biocatalyst (ω-TA-PLP). Non-natural ketone substrates were transformed in flow with excellent enantioselectivity (>99% ee). Features of this novel system include high-throughput (30-60 min residence time), clean production (no quench, workup, or purification required), high enzyme stability (the packed-bed reactor can be continuously operated for 1-10 days), and excellent mass recovery.