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

• N-phenylacetyl-DL-tert-leucine was resolved with immobilized penicillin G acylase.
• The reaction was conveniently performed in water at pH 8.0 without pH regulation.
• L-tert-Leucine was obtained in an enantiopure form (>99% ee).
• Immobilized PGA showed a long-term stability for 51 days in a RPBR system.
• Unreacted D-enantiomer was reused via racemization at 160 °C for 15 min.

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 0.4 M substrate concentration in water at pH 8.0 and 30 °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 °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.