NUCLEOSIDES AND NUCLEOTIDES .116. CONVENIENT SYNTHESES OF 3-DEAZAADENOSINE, 3-DEAZAGUANOSINE, AND 3-DEAZAINOSINE VIA RING-CLOSURE OF 5-ETHYNYL-1-BETA-D-RIBOFURANOSYLIMIDAZOLE-4-CARBOXAMIDE OR CARBONITRILE

An easy chemical synthesis of 3-deazapurine nucleosides, 3-deazainosine [1-beta-D-ribofuranosylimidazo[4,5-c]pyridin-4(5H)-one (8)], 3-deazaguanosine [6-amino-1-beta-D-ribofuranosylimidazo[4,5-c]pyridin-4(5H)-one (23)], and 3-deazaadenosine [4-amino-1-beta-D-ribofuranosylimidazo[4,5-c]pyridine (29)] is described. The approach consists of ring closure between substituents at 4- and 5-positions of the imidazole ring. Treatment of 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (2), which was readily obtained from AICA-riboside (1), with aqueous dimethylamine, followed by aqueous acetic acid gave 8 in 64% yield. 5-(2-Hydroxyiminoethyl)-1-(2,3,5-tri-O-tert-butyldimethylsilyl-beta-D-ribofuranosyl)imidazole-4-carboxamide (19) was synthesized from 3 by treatment of aqueous dimethylamine, followed by hydroxylamine hydrochloride. Dehydration of 19 was achieved by phenyl isocyanate to give 5-cyanomethyl derivative 21, from which 3-deazaguanosine (23) was easily obtained. 3-Deazaadenosine (29) was synthesized from 5-ethynyl-1-(2,3,5-tri-O-tert-butyldimethylsilyl-beta-D-ribofuranosyl)imidazole-4-carbonitrile (25).