Synthesis of 5-β-D-ribofuranosylnicotinamide and Its N-methyl Derivative. The Isosteric and Isoelectronic Analogues of Nicotinamide Nucleoside

The pyridine C-nucleosides 5-β-D-ribofuranosylnicotinamide and its N-methylpyridinium derivative (1 and 2), which are isosteric and isoelectronic, respectively, to nicotinamide nucleoside were synthesized. Condensation of 3-bromo-5-lithiopyridine with 2,4:3,5-di-O-benzylidene-D-aldehydoribose (7) afforded an allo/altro mixture of the corresponding bromopyridine derivatives, which were converted into nicotinamide C-nucleoside precursors 10. Mesylation of the hydroxyl group of 10 followed by acid hydrolysis of the product afforded the anomeric nicotinamide C-nucleosides. The β anomer 1 was separated and treated with Mel to give 2.