An enantioselective esterification of racemic naproxen by reaction with trimethylsilyl methanol was found when Candida rugosa lipase, that was chemically modified by reductive alkylation with acetaldehyde, is employed as the biocatalyst in isooctane. Increasing the degree of enzyme modification results in an enhancement: of enzyme enantioselectivity, while a maximum activity for each enantiomer was observed at 37 degrees C. However, this modification has little effect on enzyme activity and enantioselectivity at the reaction temperature higher than 50 degrees C. A comparison of kinetic behaviors for the derived and the native lipases indicates that the former can enhance the time-course stability, while decreasing the alcohol inhibition effect, enzyme activity and enantioselectivity.