5-Aza-7-deaza-2'-deoxyguanosine: Studies on the Glycosylation of Weakly Nucleophilic Imidazo-s-triazinyl Anions

Article abstract of DOI:10.1021/jo00232a015

5-Aza-7-deaza-2'-deoxyguanosine (1) has been synthesized by glycosylation of the anions of the imidazo<1,2-a>-s-triazines 3 or 4b with 2-deoxydi-O-(p-toluoyl)-α-D-erythro-pentofuranosyl chloride (7a).Glycosylation was carried out under liquid-liquid or solid-liquid phase-transfer conditions with Bu4NHSO4 or the cryptand TDA-1 as catalyst as well as in the presence of NaH.In contrast to the stereospecific glycosylation occurring at hard nucleophiles, glycosylation was not stereospecific in the case of weakly nucleophilic imidazo<1,2-a>-s-triazines; α- and β-anomerswere formed by applying the three different glycosylation methods.Configurational as well as conformational parameters of the deoxynucleosides 1 and 2 were determined by one- and two-dimensional FT-NMR spectroscopy.Both anomeric 2'-deoxyguanosine isosters exhibit the anti conformation at the N-glycosylic bond, a predominant C-2'-endo sugar puckering, and a (-sc) conformation around the C-4'-C-5' bond.