Tuning Lipase Enantioselectivity in Organic Media Using Solid-State Buffers

The enantioselectivity exhibited by Candida antarctica lipase B (CALB) in predominantly organic media has been studied for different enzyme protonation states. Alcoholysis of (±)-2-phenyl-4-benzyloxazol-5(4H)-one (1) using butan-1-ol as the nucleophile in low-water organic solvents was used as a model reaction. Using either organo-soluble bases or the newly introduced solid-state buffers of known pK a, the protonation state of the lipase was altered. By choice of the appropriate solid-state buffer or organic base, the enantioselectivity could be selectively tuned. Both Et3N and the solid-state buffer pair CAPSO/CAPSO.Na were found to increase the enantioselectivity of the reaction catalyzed by CALB and that of another lipase (Mucor miehei). Significant differences to both the enantioselectivity and catalytic rate were observed, especially under hydrated conditions where byproduct acid was formed.