加水分解酵素を用いた不斉アルコールの速度論的光学分割: エナンチオ選択性の発現機構

概要

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Mechanistic studies on the enantioselectivity in the hydrolase-catalyzed kinetic resolutions of racemic alcohols are described. Based on kinetic measurements, molecular orbital calculations and computer modeling with X-ray crystal structures of several lipases, we proposed the transition-state model that is consistent with the experimental observations such as (i) high enantioselectivity, (ii) broad substrate specificity and (iii) an empirical rule (R-preference for secondary alcohols). A large secondary alcohol having a tetraphenylporphyrin as the substituent was successfully resolved by several lipases, demonstrating the validity of our transition-state model. The S-preference of subtilisins for secondary alcohols was rationalized by applying the protocol used in the transition-state model for lipases to subtilisins. We also found that the lipasecatalyzed transesterifications of chiral alcohols in organic solvents can proceed even at -40°C. Interestingly, theE value increased with decreasing temperature, and a linear relationship was observed between In E and 1/T, from which the ΔΔH‡and ΔΔS‡ values were calculated. These thermodynamic parameters were useful for investigating the mechanism of the enantioselectivity of the hydrolases toward chiral alcohols.
社団法人有機合成化学協会の論文
2000-07-01