Purines. XXX. : Ring Fission of 3, 7-Dialkyladenines by Alkaline Hydrolysis

抄録

On treatment with boiling 1 N aqueous NaOH for 2 h, 3, 7-dialkyladenine salts (7 : R¹, R²=Me, Et, or PhCH₂; X=Br, I, or ClO₄) gave 1-alkyl-4-(N-alkylamino)-1H-imidazole-5-carboxamides (8), 1-alkyl-4-amino-1H-imidazole-5-carboxamides (11), and N⁶, 7-dialkyladenines (14) in 33-59%, 2-10%, and 2-5% yields, respectively. Under slightly miler reaction conditions, 3, 7-dimethyl-adenine hydriodide (7a : X=I) afforded 1-methyl-4-(N-methylamino)-1H-imidazole-5-carboxamide (8a) together with 3, 7-dimethylhypoxanthine (2a) as a by-product; 7-benzyl-3-methyladenine hydrobromide (7c : X=Br) furnished a small amount of 1-benzyl-4-(N-methylamino)-1H-imidazole-5-carboxamidine (5c) besides 1-benzyl-4-(N-methlamino)-1H-imidazole-5-carboxamide (8c), 1-benzyl-4-amino-1H-imidazole-5-carboxamide (11c), and 7-benzyl-N⁶-methyladenine (14c). These results are best interpreted in terms of pathways involving hydrolytic deamination, ring fission in the pyrimidide and imidazole moieties, cyclization, and Dimroth rearrangement. The instability of 7a (X=I) in aqueous alkali was compared with that of the four possible N^x, 9-dimethyl isomers, and the relative ease with which the adenine ring underwent hydrolytic ring fission was found to decrease in the order 3, 9- (17)>7, 9- (18)>1, 9- (19)>3, 7- (7a)»N⁶, 9-dimethyl isomer (20).