A 2-Propanol Treatment Increases the Enantioselectivity of Candida rugosa Lipase toward Esters of Chiral Carboxylic Acids

Crude lipase from Candida rugosa (CRL) is a poorly to moderately enantioselective catalyst for the hydrolysis of esters of 2-substituted carboxylic acids such as 2-arylpropanoic acids (E = 4-10) and 2-(aryloxy)propanoic acids (E = 2-17). Previous workers converted CRL into a high enantioselectivity form using a four-step purification procedure that included an organic solvent treatment. In this paper we report a simple 2-propanol treatment that converts crude CRL to the high enantioselectivity form. Dissolving crude commercial CRL in 50% 2-propanol followed by dialysis to remove 2-propanol increased the total activity by a factor of 1.2-1.6 and the enantioselectivity toward seven carboxylic acids by a factor of 2.3 to >25. We demonstrated synthetic use of this 2-propanol-treated CRL by resolving 10 g of methyl 2-(4-chlorophenoxy)propionate (3-methyl ester), yielding 2.8 g of product acid (93.1% ee R, a serum cholesterol-lowering compound) and 4.7 g of recovered ester (94.4% ee S), corresponding to an enantiomeric ratio of 100 for the resolution. Recent X-ray crystal structures identified two conformational forms of CRL-open and closed. We suggest that the 2-propanol treatment may increase the activity and enantioselectivity by converting the closed form of CRL to the open form.