Synthesis of Acyclic Adenine 8,N-Anhydronucleosides

Abstract

9-(4-Hydroxybutyl)adenine (10) was obtained by reaction of adenine with 4-[(2-tetrahydropyran-2-yl)oxy]butyl chloride (7) in the presence of DBU. 8-Bromo-9-(4-hydroxybutyl)adenine (13) was prepared by bromination of 10 or by alkylation of 8-bromoadenine (11) with 4-bromoethyl acetate followed by methanolysis. Tosylation of compound 13 afforded the 4-tosyloxy derivative 15 which gave on heating with methylamine or cyclopropylamine 6-methyl- (17a) or 6-cyclopropyl-7,8,9,10-tetrahydro-6H-[1,3]diazepino[1,2-e]purin-4-amine (17b), while the reaction with hydrazine afforded 7,8,9,10-tetrahydro-6H-[1,3]diazepino[1,2-e]purine-4,6-diamine (17d). Treatment of compound 13 with thionyl chloride gave 9-(4-chlorobutyl)-8-chloroadenine (18) as the main product which was transformed to 17b, 6-propyl-7,8,9,10-tetrahydro-6H-[1,3]diazepino[1,2-e]purin-4-amine (17c) or 7,8,9,10-tetrahydro-6H-[1,3]diazepino[1,2-e]purin-4-amine (17e) by reaction with cyclopropylamine, propylamine or ammonia, respectively. Compound 17e was quite stable both in acid and alkaline solutions, at room temperature or at 90 °C. Compound 13 was converted to 9-(4-hydroxybutyl)-8-methylaminoadenine (19) by reaction with methylamine. Compound 19 failed to undergo intramolecular cyclization to diazepine 17a on treatment with diphenyl carbonate, bis(4-nitrophenyl) carbonate or 1,1'-carbonyldiimidazole.