Nucleosides. CXLVIII. Synthesis of 6-(β-D-Ribofuranosyl)picolinamide. A Novel C-Nucleoside from D-Ribonolactone

Treatment of 2,4: 3,5-di-O-benzylidene-D-aldehydo-ribose (1) with 2-bromo-6-lithiopyridine afforded a mixture of the altro and alio isomers of 6-(2,4: 3,5-di-O-benzylidene-D-pentitol-1-yl)-2-bromopyridine (2 and 3, respectively). These isomers were chromatographically separated. Compound 2 was converted into 6-(β-D-ribofuranosyl)-2-bromopyridine (6) by mesylation of the 1’-hydroxyl group of 2 followed by treatment with trifluoroacetic acid. In a similar manner, the a-isomer 7 was prepared from 3. The same pyridine-C-nucleosides, 6 and 7, were also synthesized from the commercially available D-ribonolactone in seven steps. The bromo function of 2 and 3 was converted into the carboxamide group to give 6-(2,4: 3,5-di-O-benzyhdene-D-altro-pentitol-1-yl)picolinamide (10) and its alio isomer 11. Mesylation of 10 followed by trifluoroacetic acid treatment afforded 6-(β-D-ribofuranosyl)picolinamide (14). Similar treatment of 11 gave the a counterpart 15.