Purines, pyrimidines, and imidazoles. Part 52. New syntheses of some 1-β-D-arabinofuranosylaminoimidazoles and of related purine nucleosides, including 9-β-D-arabinofuranosyladenine

Ethyl 5-amino-1-β-D-arabinofuranosylimidazole-4-carboxylate and the corresponding carboxamide have been prepared by reaction of ethyl 5-aminoimidazole-4-carboxylate or the carboxamide, respectively with 2,3,5-tri-O-benzyl-α-D-arabinofuranosyl chloride (but not the bromide or iodide) and deblocking. Reaction of the nucleoside ester with formamidine acetate gave 9-β-D-arabinofuranosylhypoxanthine. 5-Amino-4-cyano-1-β-D-arabinofuranosylimidazole obtained by dehydration of the benzylated carboxamide or by direct glycosylation of 5-amino-4-cyanoimidazole and debenzylation of the product, when heated with triethyl orthoformate and ammonia, gave 9-β-D-arabinofuranosyladenine. 2,3,5-Tri-O-benzylarabinofuranosyl chloride with sodium azide, followed by reduction of the glyosyl azide formed with platinic oxide, and condensation of the arabinosylamine produced with ethyl N-(carbamoylcyanomethyl)formimidate gave a mixture of 2,3,5-tri-O-benzyl 1-α- and -β-D-arabinofuranosylimidazole 4-carboxamides. Reduction of the azide with lithium aluminium hydride followed by debenzylation of the product gave, in addition to the two anomers, 5-amino-1-D-arabinitylimidazole-4-carboxamide.