AB-INITIO AND SEMIEMPIRICAL INVESTIGATIONS OF THE COMPLEXATION OF METHYL PYRUVATE BY AMMONIA AND THE AMMONIUM CATION

The optimal structures and energies of the methyl pyruvate system complexed by NH3 and NH4+ have been calculated using the ab initio method at various levels of theory. The results indicate that both complexes are stable, with a much larger complexation energy for the second one due to the stabilizing electrostatic interactions. These conclusions, which are in agreement with semiempirical calculations performed using reaction potentials, provide valuable information concerning the interaction occurring between the substrate and the nitrogen atom of the stereogenic centre of cinchona alkaloids, which are used for chiral induction in the enantioselective hydrogenation of alpha-ketoesters.