Lipase-catalysed two-step desymmetrization of 2-methylmalonic dipyrazolide for preparation of optically pure enantiomer in organic solvents

A lipase-catalysed two-step butanolytic desymmetrization process for the preparation of pyrazolidyl butyl (S)-2-methylmalonate from 2-methylmalonic dipyrazolide was developed. The best reaction condition of using lipase PS-D in anhydrous n-hexane at 55 °C was first selected, leading to high yield and enantiomeric excess for the remained (S)-enantiomer. The kinetic analysis by considering the competitive inhibition from butanol was then carried out for obtaining the stereoselectivity of E₁ = 11.2 for the first desymmetrization and enantiomeric ratio of E₃E₂ ⁻¹=11.8 for the subsequent kinetic resolution. The thermodynamic analysis furthermore revealed that the enzyme stereodiscrimination was enthalpy-driven for the desymmetrization step, but changed as entropy-driven for the kinetic resolution step.