Models for NADH coenzymes. Isotope effects in the N-benzyldihydronicotinamide/N-bensylnicotinamide salt transhydrogenation reaction

The transhydrogenation reaction was studied in N-benzyl-1,4-dihydronico-tinamide/N/benzylnicotinamide chloride systems with tritium and/or 14C labelling. It was shown that the measured secondary isotope effects during transhydrogenation are exactly opposite to those predicted by considering changes in hybridization at the 4 position in going to the transition state. In addition, although the evidence supports a multistep process, the 1,2- or 1,6-dihydropyridine may be excluded as an obligatory intermediate