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 VS/VR = 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 VS/VR = 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 VS/VR = 26 for 2 containing a 3-hydroxy moiety in comparison with VS/VR = 323 for (R,S)-ethyl 2-hydroxy-2-phenylacetate containing a 2-hydroxy moiety using SNSM-87 immobilized on Eupergit C 250L.