Unexpected enantioselectivity and activity of penicillin acylase in the resolution of methyl 2,2-dimethyl-1,3-dioxane-4-carboxylate

The penicillin acylase (PA) from E. coli catalyzes the hydrolytic kinetic resolution of methyl 2,2-dimethyl-1,3-dioxane-4-carboxylate with remarkably high enantioselectivity and catalytic efficiency. This result is highly unusual as this ester does not contain the phenylacetic acid residue, normally considered to be a prerequisite for high activity and enantioselectivity in PA catalyzed resolutions. The apparent enantioselectivity (Eapp) was found to be high (>50) at neutral or slightly acidic pH and to decrease at more alkaline pH (>7.5) due to significant non-specific chemical hydrolysis. Similarly, enantioselectivity increased with decreasing temperature. The substrate concentration had only a slight effect on enantioselectivity and activity. The rate of hydrolysis of ester 1 is comparable to that for PA’s “natural” substrate, penicillin G.