Stereoselective Glycosylation of Nitrobenzimidazole Anions: Synthesis of 1,3-Dideaza-2′-deoxyadenosine and Related 2′-Deoxyribofuranosides

The synthesis of 1,3-dideaza-2′-deoxyadenosine (1) and related benzimidazole 2′-deoxyribonucleosides is described. Solid-liquid phase-transfer glycosylation of 5(6)-nitrobenzimidazole (9) or 4(7)-nitrobenzimidazole (15) in acetonitrile with 1-chloro-2-deoxy-3,5-bis-O -(4-methylbenzoyl)-α-D-erythro-pentofuranose (10) gave regioisomeric N-1 and N-3 β-D-2′-deoxyribofuranosides. The glycosylation yield, as well as the ratio of anomers and regioisomers, was altered by use of either tris[2-(2-methoxyethoxy)ethyl]amine (TDA-1) or [18]crown-6 as phase-transfer catalysts and potassium hydroxide or potassium carbonate as inorganic bases, respectively. Zemplén-deprotection and subsequent catalytic hydrogenation afforded the corresponding amino compounds 1, 2, 4, 5 and 7. Structural proof of anomeric and regio-isomeric compounds was made on the basis of ¹H- and ¹³C-NMR spectroscopy. The benzimidazole 2′-deoxyribofuranosides 4 and 5 exhibit strong fluorescence at λ_max =362 and 395 nm, respectively. 1,3-Dideaza-2′-deoxyadenosine (c¹c³A_d, 1) is more stable in 1 N hydrochloric acid than dA (3a). Under alkaline conditions, compound 1 decomposes whereas the regioisomer 2 is stable. Compound 1 is no substrate for adenosine deaminase.