8‐Aza‐2′‐deoxyguanosine and Related 1,2,3‐Triazolo[4,5‐ d ]pyrimidine 2′‐Deoxyribofuranosides

The synthesis of 8‐azaguanine N 9 ‐, N 8 ‐, and N 7 ‐(2′‐deoxyribonucleosides) 1–3 , related to 2′‐deoxyguanosine ( 4 ), is described. Glycosylation of the anion of 5‐amino‐7‐methoxy‐3 H ‐1,2,3‐triazolo[4,5‐ d ]pyrimidine ( 5 ) with 2‐deoxy‐3,5‐di‐ O ‐(4‐toluoyl)‐α‐ 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 12a . The anomeric configuration as well as the position of glycosylation were determined by combination of UV, 13 C‐NMR, and 1 H‐NMR NOE‐difference spectroscopy. The 2‐amino‐8‐aza‐2′‐deoxyadenosine ( 13 ), obtained from 7a , was deaminated by adenosine deaminase to yield 8‐aza‐2′‐deoxyguanosine ( 1 ), whereas the N 7 ‐ and N 8 ‐regioisomers were no substrates 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 ).