Highly efficient production of chiral amines in batch and continuous flow by immobilized ω-transaminases on controlled porosity glass metal-ion affinity carrier

In this study, two stereocomplementary omega-transaminases from Arthrobacter sp. (AsR-omega TA) and Chromobacterium violaceum (Cv-omega TA) were immobilized via iron cation affinity binding onto polymer-coated controlled porosity glass beads (EziG (TM)). The immobilization procedure was studied with different types of carrier materials and immobilization buffers of varying compositions, concentrations, pHs and cofactor (PLP) concentrations. Notably, concentrations of PLP above 0.1 mM were correlated with a dramatic decrease of the immobilization yield. The highest catalytic activity, along with quantitative immobilization, was obtained in MOPS buffer (100 mM, pH 8.0, PLP 0.1 mM, incubation time 2 h). Leaching of the immobilized enzyme was not observed within 3 days of incubation. EziG-immobilized AsR-omega TA and Cv-omega TA retained elevated activity when tested for the kinetic resolution of rac-alpha-methylbenzylamine (rac-alpha-MBA) in single batch experiments. Recycling studies demonstrated that immobilized EziG(3)-AsR-omega TA could be recycled for at least 16 consecutive cycles (15 min per cycle) and always affording quantitative conversion (TON ca. 14,400). Finally, the kinetic resolution of rac-alpha-MBA with EziG(3)-AsR-omega TA was tested in a continuous flow packed-bed reactor (157 mu L reactor volume), which produced more than 5 g of (S)-alpha-MBA (> 49% conversion,> 99% ee) in 96 h with no detectable loss of catalytic activity. The calculated TON was more than 110,000 along with a space-time yield of 335 g L-1 h(-1).