(397bn) A Lipase-Cyclodextran Conjugate With Improved Enantioselectivity
Enzymatic catalysis has been widely applied in the preparation of chiral compounds with high activity and selectivity. In general, asymmetric synthesis and chiral resolution are the two main approaches to produce chiral chemicals. Lipase, a class of ester hydrolase, has been employed in the kinetic resolution of racemic esters. However, the enantioseletivity of native lipase sometimes still cannot meet the criteria of practical use because of the unsatisfied selectivity, leaving the rational design and engineering of lipase a tough challenge. Here, we present a new method to alter the enantioselectivity of lipase by conjugating the enzyme with a chirality ‘recognizer’ such as β-cyclodextrans (β-CD). Candida antarctic lipase B (CALB) was selected as a model enzyme to conjugate with β-CD via a click reaction. (R,S)-methyl mandelate and (R,S)-methyl cyclohexylphenylglycolate were used as substrates to examine the stereoselectivity of the β-CD modified CALB. Since the β-CD has different binding abilities towards R- and S-substrates, the lipase-CD conjugate showed an altered enantioselectivity. For instance, the conjugation of β-CD facilitated the enzymatic hydrolysis of (R)-methyl mandelate but had no distinct influence on the (S)-isomer. A typical result showed that the enantiomeric ratio (E ratio) was improved from 5 to 30 (at a conversion of 40%) and the enantiomeric excess (ee) of reached higher than 85%. The mechanism of the improvement of enzymatic enantioselectivity will be also discussed in this presentation. This type of enzyme-β-cyclodextran conjugate offers a novel chemical method for improving, controlling or even inversely altering the enzymatic enantioseletivity, which would have much promise in the applications of enzymatic resolution.