Hexamethyldisilazane → 7-Amino-3-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)thiazolo[4,5-d]pyrimidin-2-one

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Reaction Steps

Compound 30 (1.22 g, 7.25 mmol) was glycosylated as described for the preparation of 6, requiring HMDS (35 mL), benzoyl-blocked sugar (5: 4.4 g, 8.7 mmol) and TMS-triflate (2.0 mL, 10.3 mmol). After stirring overnight at room temperature, the reaction mixture was refluxed for 2 days and then worked up in the usual manner. The crude mixture was subjected to flash silica gel column chromatography using a gradient of methylene chloride to methylene chloride-acetone 10:1 (v/v) and yielded two products. The first to elute from the column was assumed by 1H NMR to be a bis-glycoside which amounted to 660 mg. The second and major product off the column was obtained as a foam and assigned as the desired 3-ribosyl isomer by UV and 1H NMR: yield 1.04 g (24%): UV λmax (EtOH) 232 nm (ε), 283 (): 1H NMR (DMSO-d6) δ 6.34 (t, 1H, C1 ,H), 7.39-7.98 (m, 17H, benzoyl aromatics and NH2, 8.19 (s, 1H, C5H), and other sugar protons. Anal. Calcd. for C, 60.78: H, 3.95: N, 9.15: S, 5.23. Found: 3.93: N, 8.13: S, 4.85.

Provenance & Evidence