Enantioselective transacetylation of (R,S)-β-citronellol by propanol rinsed immobilized Rhizomucor miehei lipase

Background: Use of enzymes in low water media is now widely used for synthesis and kinetic resolution of organic compounds. The frequently used enzyme form is the freeze-dried powders. It has been shown earlier that removal of water molecules from enzyme by rinsing with n-propanol gives preparation (PREP) which show higher activity in low water media. The present work evaluates PREP of the lipase (from Rhizomucor miehei) for kinetic resolution of (R, S)-beta-citronellol. The acylating agent was vinyl acetate and the reaction was carried out in solvent free media. Results: The PREP, with 0.75% (v/v, reaction media) water, was indeed found to be more efficient and gave 95% conversion to the ester. Using this PREP, with no added water, 90% ee for (R)-(+)-beta-citronellyl acetate at 45% conversion (E = 42) was obtained in 4 h. The control with freeze-dried enzyme, with zero water content, gave 78% ee at 30% conversion (E = 13). FT-IR analysis showed that PREP had retained the alpha-helical content of the enzyme. On the other hand, freeze-dried enzyme showed considerable loss in the alpha-helical content. Conclusion: The results show that PREP may be a superior biocatalyst for enantioselective conversion by enzymes in low-water media.