Dehydration of 5-(cyanomethylamino)-1-methyl-1H-imidazole-4-carboxamide (14a) with a combination of phosphorus oxychloride and triethylamine afforded the nitrile 17a. This compound underwent selective hydration at the cyanamide moiety to furnish the urea 18a followed by cyclization to 3, 9-dimethylisaguaninae (19a) under alkaline conditions. Similar dehydration of the nucleoside analog 14b followed by treatment with 0.1 N aqueous sodium hydroxide led to the first access to 3-methylisoguanosine (19c). Although 3-methylisoguanosine (19c) proved to undergo hydrolysis at the N-glycosidic bond most slowly among the known 3-methyl-9-β-D-ribofuranosylpurines in 0.1 N hydrochloric acid at 25°C, the rate was 650 times faster than that for the unmethylated isoguanosine (3).
用
磷氧
氯化物和
三乙胺组合对5-(
氰基甲基
氨基)-1-甲基-
1H-咪唑-4-羧酰胺(14a)进行脱
水反应生成了腈化合物17a。该化合物在
氰胺部分经历了选择性
水合作用,形成了
尿素18a,然后在碱性条件下环化生成3, 9-二甲基异
尿苷(19a)。类似地,核苷类似物14b的脱
水反应后,处理0.1 N
水合
氢氧化钠,首次获得了3-甲基异
尿苷(19c)。尽管在0.1 N
盐酸中,3-甲基异
尿苷(19c)在25°C下的N-糖苷键
水解速度在已知的3-甲基-9-β-
D-核糖呋喃半
嘌呤中最慢,但其速度仍比未甲基化的异
尿苷(3)快650倍。