On the relationship between enzymatic enantioselectivity in organic solvents and enzyme flexibility

The enantioselectivities of subtilisin Carlsberg and alpha-chymotrypsin sus pended in seven anhydrous solvents were determined in the acylation of sec- phenethyl alcohol with vinyl butyrate. In every case, both a dry lyophilize d enzyme and one hydrated by a prior exposure to a humid environment were u sed as asymmetric catalysts in a given solvent. This hydration was found to boost the water content of the enzyme which, in turn, is known to enhance the enzyme's conformational flexibility. These data together resulted in th e following correlation: as enzyme flexibility increases, the enantioselect ivity decreases or remains the same. This relationship is opposite to that recently claimed for subtilisin by Broos et at. (Broos, J., Visser, A.J.W.G ., Engbersen, J.F.J., Verboom, M., van Hock, A. and Reinhoudt, D.N. (1995) J. Am. Chem. Soc., 117, 12 657-12 663). The basis for their conclusion is c ritically analyzed herein and found to be questionable.