THE ENANTIOMERIC RATIO - ORIGIN, DETERMINATION AND PREDICTION

The enantiomeric ratio E = (k(cat)(R)/K-m(R))/(k(cat)(S)/K-m(S)) offer s a concise representation of the enantioselective properties of an en zyme in reactions that involve chiral compounds. Both as a measure of the intrinsic selectivity of the catalyst, and as a parameter to model the performance of enzymatic processes for the production of enantiop ure fine-chemicals, its merits have been well-recognized. Several meth ods for the determination of E exist. The scope and limitations of the se methods are evaluated in terms of accuracy and feasibility. There a ppears to be no single method that is both reliable and readily applic able in all cases. Complementary methods, however, are available. The outstanding characteristics of the enantiomeric ratio as a quantitativ e measure of the effects of physical and chemical conditions on the in trinsic enantioselectivity of enzymes are presented in terms of the di fference in Gibbs energies of the diastereomeric enzyme-substrate tran sition states. The prospects of molecular modeling strategies for the prediction of E are discussed. (C) 1997 Elsevier Science Inc.