Novel synthesis of seco type of acyclo C-nucleosides of 1,2,4-triazole and1,2,4-triazolo[3,4-b][1,3,4]thiadiazine

The seco C-nucleosides 3-(1,2,3,4,5-penta-O-acetyl-D-gluco- and D-galacto-p entitol-1-yl)-1H-1,2,4-triazole (8 and 9) were obtained in a one pot by dea mination and dethiolation of 4-amino-3-(D-gluco- and D-galacto-pentitol-1-y l)-5-mercapto-1,2,4-triazoles (1 and 2), respectively, using sodium nitrite in orthophosphoric acid and subsequent acetylation. Condensation of 1, 2, and 4-amino-3-(D-glycero-D-gulo-hexitol-1-yl)-5-mercapto-1,2,4-triazole (12 ) with phenacylbromide (11) afforded the corresponding 3-(D-gluco-, D-galac topentitol-1-yl)) and 3-(D-glycero-D-gulo-hexitol-1-yl)-6-phenyl-7H-1,2,4-, 2,4-triazolo[3,4-b] [1,3,4] thiadiazines (15, 16, and 17). Acetylation of 1 5-17 gave the penta- and hexa-O-acetyl derivatives 18-20, respectively. The structures were confirmed by using H-1,C-13, and 2D NMR spectra, DQFCQSY, HMQC, and HMBC experiments. The favored conformational structures were dedu ced from the vicinal coupling constants of the protons.