ABSTRACT
Lipases are important catalysts in chiral synthesis due to their wide substrate recognition combined with a high stereoselectivity. We demonstrate here that the state, free or immobilized, of Candida antarctica lipase B (CaLB) affects enantioselectivity and also alters the temperature dependancy of the enzyme. This indicates that CaLB undergoes various conformations induced by its interaction with the different immobilization supports studied. Molecular imprinting experiments, using immobilized enzyme co-dried with mimic substrate molecules, enhanced the enantiomeric ratio two-fold or three-fold, depending on the immobilization support. The structure of the acyl donor has a pronounced effect on CaLB catalyzed resolution, due to the proximity of the acyl and alcohol moieties during catalysis. When the acylation of pentan-2-ol was examined, we found that the 3C methyl propanoate donor afforded the highest resolution. Trans-(Z)-cyclooct-5-en-1,2-diol was used as a model racemic substrate to study the ability of lipase to catalyze the resolution of difunctionalized compounds. There was a clear enhancement in the enantiomer selectivity of the biotransformation of the diol when vinyl butanoate is used as the acyl donor. The conversion and enantiomeric excess of (1R,2R)-monoacetates were enhanced, using immobilized CaLB, when the chain length of the donors increased from C2 to C4.
