Construction and operation of a fibrous bed reactor with immobilized lactonase for efficient production of (R)-α-hydroxy-γ-butyrolactone

Optically active (R)-α-hydroxy-γ-butyrolactone (R-HBL) was produced via enantioselective hydrolysis of racemic HBL using a lactonase extracted from Fusarium proliferatum ECU2002 (FPL). Different carriers were examined for immobilizing FPL and the highest activity was observed when the enzyme was adsorbed onto cotton cloth followed by cross-linking with glutaraldehyde. A fibrous bed reactor (FBR) was constructed by packing a piece of cotton cloth (∼2 g) coiled together with a wire net into a glass column (Ø1.5 cm × 12 cm) thermostated at 30 °C. Kinetic resolution of RS-HBL was carried out semi-continuously in the FBR by recirculating a racemic lactone solution through the reactor at a certain flow rate. The performance and productivity of the FBR were evaluated by several critical parameters, including enzyme load, initial RS-HBL concentration and so on. Immobilized FPL (IFPL, ∼40 U) per 50 ml of working volume was found to be the optimal enzyme load, and the most suitable substrate concentration was 750 mM at 30 °C with an appropriate height to diameter (H/D) ratio (5.0). The IFPL-catalyzed kinetic resolution of RS-HBL was successfully operated in the FBR for 60 batches, with an average productivity of 2.48 g l−1 h−1 (R-HBL) in high optical purity (90.0–96.4% ee) in the case of semi-continuous operation.