8-AZA-2'-DEOXYGUANOSINE AND RELATED 1,2,3-TRIAZOLO[4,5-D]PYRIMIDINE 2'-DEOXYRIBOFURANOSIDES

The synthesis of 8-azaguanine N-9-, N8-, and N7-(2'-deoxyribonucleosid es) 1-3, related to 2'-deoxyguanosine (4), is described. Glycosylation of the anion of amino-7-methoxy-3H-1,2,3-triazolo[4,5-d]pyrimidine (5 ) with ,5-di-O-(4-toluoyl)-alpha-D-erythro-pentofuranosyl chloride (6) afforded the regioisomeric glycosylation products 7a/7b, 8a/8b, and 9 (Scheme 1) which were detoluoylated to give 10a, 10b, 11a, 11b, and 1 2a. The anomeric configuration as well as the position of glycosylatio n were determined by combination of UV, C-13-NMR, and H-1-NMR NOE-diff erence spectroscopy. The 2-amino-8-aza-2'-deoxyadenosine (13), obtaine d from 7a, was deaminated by adenosine deaminase to yield 8-aza-2'-deo xyguanosine (1), whereas the N7- and N8-regioisomers were no substrate s of the enzyme. The N-glycosylic bond of compound 1 (0.1 N HCl) is ca . 10 times more stable than that of 2'-deoxyguanosine (4).