Kinetic Resolution of (R)- and (S)-3-Alkanols by Lipase Catalyzed Transesterification with Isopropenyl Acetate in Organic Solvent

摘要

Kinetic resolution of (R)- and (S)-3-alkanols by enzymatic transesterification has been studied using Pseudomonas cepacia lipase, isopropenyl acetate as an acetylating reagent, five alcohols and some organic solvents. The optical resolution data did not fit the previously reported format: the enantioselectivity (E: the rate ratio as the reaction is irreversible) showed the maxima against the extent of conversion (c) for all system used and the correlation between log E and c was different depending on the substrate and solvent. The optical resolution of (S)-3-alkanol with above 95% of enantiomeric excess (ee) was attained by controlling c. In contrast (R)-3-alkanol with ee > 95% could not be resolved from (RS)-3-alkanol even at low c because of the moderate enantioselectivity. Kinetic resolution of enantiomers in enantiomerically enriched alcohols was carried out: the ee values of resolved alcohols showed an excellent agreement with those determined by the previously reported equations using the optical resolution data and (R)- and (S)-3-alkanols with high ee could be resolved by controlling c and the initial optical purity of substrate. Based on the above observations, optically pure (R)- and (S)-3-octanols (ee ≧ 99%) were resolved from racemic 3-octanol by repeating the transesterification three times and twice, respectively.