Efficient preparation of enantiopure L-tert-leucine through immobilized penicillin G acylase catalyzed kinetic resolution in aqueous medium

Racemic DL-tert-leucine ((DL)-Tle) was resolved to obtain enantiopure (L)-Tle through enantioselective hydrolysis of its N-phenylacetyl derivative with immobilized penicillin G acylase (PGA). The effects of pH, reaction temperature, substrate concentration and reaction time on the reaction were investigated. The reaction was conveniently carried out at 0.4M substrate concentration in water at pH 8.0 and 30 degrees C. Under the optimized reaction conditions, L-Tle was obtained in an enantiopure form (> 99% ee) with 45.8% substrate conversion after 4 h. The thermal stability and operational stability of immobilized PGA were examined. Furthermore, the preparation of L-Tle was successfully performed in a recirculating packed bed reactor (RPBR) system and immobilized PGA exhibited a long-term stability for 51 days with a slight decrease of activity. The isolated (D)-enantiomer was racemized at 160 degrees C for 15 min and reused as substrate. The results obtained clearly demonstrated a potential for industrial application of immobilized PGA in the preparation of L-Tle through enantioselective hydrolysis of its N-phenylacetyl derivative. (C) 2013 Elsevier B.V. All rights reserved.