Novel dideoxynucleoside isosteres

Novel 5-aza-7-deaza isosteres of the anti-HIV compounds, dideoxyinosine (ddI) and dideoxyguanosine (ddG), have been prepared by glycosylation of the corresponding isosteric bases with appropriately tailored dideoxyribose components. The glycosylation reactions were regiospecific and the position of glycosylation was established by UV and high-field NMR data. However, attempted preparation of the 3- deaza-5-aza isostere of dideoxyinosine led to a different regioisomer, a ring-extended dideoxycytidine analogue, whose structure was established by X-ray crystallographic data. The 5-aza-7-deaza isosteres of ddI and ddG were more stable with respect to hydrolytic cleavage than ddI and ddG.