Efficient synthesis of fused isothiazolo C-nucleosides. III. Synthesis of 7-substituted isothiazolo[4,5-d]pyrimidine C-nucleosides

The Divakar-Reese procedure has been successfully applied for transforming 7-oxo-isothiazolo[4,5-d]pyrimidine C-nucleosides (4a,b, 5a,b, 6a) via 1,2,4 -triazol-1-yl intermediates (7a,b, 8a,b) into various 7-substituted C-nucle osides 15a,b, 16a,b, 17a, 18a, 19a,b, 20a,b; their subsequent deprotection provides novel types of unusual C-glycosides 22b, 23a, 24a,b, 25b, 26b. C-Nucleosides, possessing on its heterocyclic base other than naturally occ uring oxo- or amino substituents, are important model compounds for biologi cal or medicinal studies (2,3). We want to report on the synthesis of novel 7-substituted isothiazolo = [4,5-d]pyrimidine C-nucleosides. As we could s how in previous papers (1,4), there exists a simple approach to the protect ed C-glycosides 4-6.