Hydrolytic resolution of (R,S)-3-hydroxy-3-phenylpropionates by esterase from Klebsiella oxytoca: Effects of leaving alcohol, covalent immobilization and aqueous pH

The kinetic analysis for hydrolytic resolution of (R) and (S)-ethyl 3-hydroxy-3-phenylpropionate in biphasic media is carried out via a thermally stable esterase (SNSM-87) from Klebsiella oxytoca. The resultant kinetic constants are compared with those using (R,S)-ethyl 2-substituted carboxylic acid ester as the substrate. An optimal enantioselectivity of V_S/V_R = 16 for 4 using free SNSM-87 is rationalized via the structure-reactivity correlations in terms of logarithms of specificity constants varied with the inductive parameter of leaving alcohol moiety, and can further increase to an acceptable value of V_S/V_R = 37 using SNSM-87 immobilized on Sepabeads^@ EC-HA. The pH-reactivity profiles for all enzyme preparations are analyzed in order to elucidate the modest enantioselectivity of V_S/V_R = 26 for 2 containing a 3-hydroxy moiety in comparison with V_S/V_R = 323 for (R,S)-ethyl 2-hydroxy-2-phenylacetate containing a 2-hydroxy moiety using SNSM-87 immobilized on Eupergit C 250L.