The catalyzed reaction of (R,S)-1-phenylethanol and S-ethyl thio octanoate in lipase B from Candida Antarctica is studied using density functional theory methods. Quantum mechanics cluster approach is used to model the enzyme’s active site. The results show that the catalytic triad amino acids of the enzyme’s active site do not abstract the alcoholic proton of 1-phenylethanol before the nucleophilic attack of the alcohol to the ester. A two-step mechanism is proposed for the reaction of the R enantiomer of the alcohol with the ester. However, the results show no path for the S enantiomer. In other words, the results show the enantioselectivity of the enzyme. This enantioselectivity is due to different hydrogen bonding patterns of the two enantiomers of the alcohol. In the optimized structures of the modeled reactionsthe OH group of the R enantiomer is directed toward Ser-105, while the OH group of the S enantiomer is far from Ser-105 and is directed toward Thr-40.
