NOVEL SYNTHESIS OF seco TYPE OF ACYCLO C-NUCLEOSIDES OF 1,2,4-TRIAZOLE AND 1,2,4-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-pentitol-1-yl)-1H-1,2,4-triazoles (8 and 9) were obtained in a one pot by deamination and dethiolation of 4-amino-3-(D-gluco- and D-galacto-pentitol-1-yl)-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-galacto-pentitol-1-yl) and 3-(D-glycero-D-gulo-hexitol-1-yl)-6-phenyl-7H-1,2,4- triazolo[3,4-b][1,3,4] thiadiazines (15, 16, and 17). Acetylation of 15–17 gave the penta- and hexa-O-acetyl derivatives 18–20, respectively. The structures were confirmed by using ¹H, ¹³C, and 2D NMR spectra, DQFCOSY, HMQC, and HMBC experiments. The favored conformational structures were deduced from the vicinal coupling constants of the protons.