Complexation equilibrium in a substrate- MgCl2(CaCl2)-Pd/C catalytic system and the influence of its position on asymmetric induction in hydrogenation ofN-acetyl-dehydrophenylalanyl-S-proline

The role of Ca and Mg salts as promoters of asymmetric induction in hydrogenation ofN-acetyl-dehydrophenylalanyl-S-proline in a substrate— MX2—Pd/C catalytic system was studied. The data of potentiometric titration,1H NMR spectroscopy, and the value of diastereomeric excess (de) of the resultingN-acetyl-R-phenylalanyl-S-proline indicate the complexation of the substrate with calcium and magnesium chlorides in an alcoholic solution. Ionization and equilibrium constants of the complex were determined. Excess salt shifts the equilibrium toward the complex formation, which increasesde up to 70 %.