Ionic Liquid Engineering for Lipase-Mediated Optical Resolution of Secondary Alcohols: Design of Ionic Liquids Applicable to Ionic Liquid Coated-Lipase Catalyzed Reaction

A rational design of phosphonium ionic liquid for ionic liquid coated-lipase (ILI-PS)-catalyzed reaction has been investigated: very rapid transesterification of secondary alcohols was accomplished when IL1-PS was used as catalyst in tributyl((2-methoxyethoxy)methyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P-444MEM][NTf2]) or N-ethyl-N-((2-methoxyethoxy)methyl)-N-methylethanaminium bis(trifluoromethanesulfonyl)amide ([N-221MEM][NTf2]) as solvent with excellent enantioselectivity. It was also revealed that ammonium ionic liquid influenced the lipase reactivity more strongly than phosphonium ionic liquids. Increased K-cat, value was suggested to be the most important factor at work in IL1-PS in these ionic liquid solvents. The K-cat value of (S)-1-phenyethanol in [N-444MEM][NTf2] was similar to that of i-Pr2O, and 1.6-fold acceleration was achieved for (R)-1-phenylethanol. On the other hand, the K-m value for (R)-isomer in [N-444MEM][NTf2] was slightly larger than the reaction in i-Pr2O, while it was significantly reduced for (S)-isomer. These results suggest that solvent provides a certain impact on the reactivity of the enzyme protein of IL1-PS.