Kinetic resolution of racemic 2-substituted 3-cyclopenten-1-ols by lipase-catalyzed transesterifications: A rational strategy to improve enantioselectivity

The effect of the acyl group of acylating agents on the enantioselectivity in the Pseudomonas cepacia lipase-catalyzed acylations of racemic alcohols has been studied. 2-[(N,N-Dimethylcarbamoyl)-methyl]-3-cyclopenten-1-ol (1) and 2-[2-(tert-butyldimethylsilyloxy)ethyl]-3-cyclopenten-1-ol (4) were resolved with a variety of enantioselectivities. In the case of alcohol 1, the enantiomeric ratio (the E value) was increased by changing the acylating agent from vinyl acetate (E = 30) to vinyl butyrate (E = 156) and dropped substantially with longer acyl donors. With vinyl chloroacetate, the reaction rate was fast and the enantioselectivity was high (E = 89), whereas the resolution with vinyl trifluoroacetate resulted in a very poor enantioselectivity (E = 4). The bulky acylating agent, vinyl pivalate, gave a moderate enantioselectivity (E = 15). In the case of alcohol 4, the enantioselectivities were excellent (E > 142) except vinyl pivalate (E = 12). It is indicated that the acyl group transiently attached at the active site of the lipase acts as a stereochemical controller. The solvent effect is also described briefly. A clear correlation was observed between the E values and the log P values of the organic solvents; the smaller the log P value of the solvent, the higher the E value.