Efficient synthesis of 3,5-dicarbamoyl-1,4-dihydropyridines from pyridinium salts. Key molecules in understanding NAD(P)+/NAD(P)H pathways

3,5-Dicarbamoyl-1,4-dihydropyridines were prepared in high yields using a green protocol by reductionof the corresponding pyridinium salts in aqueous buffered sodium dithionite solutions. The pH value is a fundamental parameter for the reduction step and depends on the nature of substituent groups at positions 1, 3, and 5 of the pyridinium salts. These 3,5-dicarbamoyl dihydropyridines show a lower tendency towardsoxidation and a higher stability than N-benzyl-3-carbamoyl- 1,4-dihydropyridine at low pH values.