Crosslinked enzyme aggregates of hydroxynitrile lyase partially purified from Prunus dulcis seeds and its application for the synthesis of enantiopure cyanohydrins

Hydroxynitrile lyases are powerful catalysts in the synthesis of enantiopure cyanohydrins which are key synthons in the preparations of a variety of important chemicals. The response surface methodology including three-factor and three-level Box-Behnken design was applied to optimize immobilization of hydroxynitrile lyase purified partially from Prunus dulcis seeds as crosslinked enzyme aggregates (PdHNL-CLEAs). The quadratic model was developed for predicting the response and its adequacy was validated with the analysis of variance test. The optimized immobilization parameters were initial glutaraldehyde concentration, ammonium sulfate saturation concentration, and crosslinking time, and the response was relative activity of PdHNL-CLEA. The optimal conditions were determined as initial glutaraldehyde concentration of 25% w/v, ammonium sulfate saturation concentration of 43% w/v, and crosslinking time of 18 h. The preparations of PdHNL-CLEA were examined for the synthesis of (R)-mandelonitrile, (R)-2-chloromandelonitrile, (R)-3,4-dihydroxymandelonitrile, (R)-2-hydroxy-4-phenyl butyronitrile, (R)-4-bromomandelonitrile, (R)-4-fluoromandelonitrile, and (R)-4-nitromandelonitrile from their corresponding aldehydes and hydrocyanic acid. After 96-h reaction time, the yield-enantiomeric excess values (%) were 100-99, 100-21, 100-99, 83-91, 100-99, 100-72, and 100-14%, respectively, for (R)-mandelonitrile, (R)-2-chloromandelonitrile, (R)-3,4-dihydroxymandelonitrile, (R)-2-hydroxy-4-phenyl butyronitrile, (R)-4-bromomandelonitrile, (R)-4-fluoromandelonitrile, and (R)-4-nitromandelonitrile. The results show that PdHNL-CLEA offers a promising potential for the preparation of enantiopure (R)-mandelonitrile, (R)-3,4-dihydroxymandelonitrile, (R)-2-hydroxy-4-phenyl butyronitrile, and (R)-4-bromomandelonitrile with a high yield and enantiopurity.