Enzymatic Synthesis of Pyridine Nucleotides. Structural Property of Some New NAD-analogs, and Base Conditions Available for the Analog Formation

Some new β-NAD-analogs were prepared by a base-exchange reaction catalyzed by pig-brain NADase. The analogs produced from methyl 4-(methylamino)- and 4-(dimethylamino)nicotinates were proved to be 1,4-dihydropyridine form. On the contrary, the analog obtained from 4-(acetylamino)nicotinamide was shown to be a quaternary pyridinium form. Moreover, an unexpected analog of 1,4-dihydro-4-pyridinone form was given by 4-methoxynicotinamide. It was shown to be indispensable for the formation of NAD-analog that the ring nitrogen of pyridine bases concerned should at least be free from protonation around pH 7. Interestingly nicotinic acids with 4-amino, methylamino, and dimethylamino groups were found to be much more basic for the ring nitrogen atom than their respective methyl esters.