Purines. XLIX. Synthesis and Proton Nuclear Magnetic Resonance Study of 3,7-Dialkylxanthines and 1,3,7-Trialkylxanthines.
作者:Tozo FUJII、Tohru SAITO、Katsumi TAMURA
DOI:10.1248/cpb.39.2855
日期:——
A general synthetic route to 3, 7-dialkylxanthines (type 9) from 3, 7-dialkyladenines (6) [hence from 3- or 7-alkyladenines (11 or 10)] has been established. The route started with ethoxycarbonylation of 1-alkyl-4-(alkylamino)-1H-imidazole-5-carboxamides (7), readily obtainable from 6 by alkaline hydrolysis, and proceeded through cyclization of the resulting carbamates (8) under alkaline conditions. Alkylation of 9 with alkyl halide in N, N-dimethylformamide in the presence of anhydrous K2CO3 extended the above synthetic route to the 1, 3, 7-trialkylxanthine level (type 14). Hydrogenolytic debenzylation of 3-benzyl-1, 7-dimethylxanthine (16), prepared by following this general synthetic route, furnished paraxanthine (26) in fair yield. Conversion of 26 into 3-(4-hydroxy-3-nitrobenzyl)-1, 7-dimethylxanthine (24), isomeric with the bryozoan purine phidolopin (2), was effected through aralkylation with 4-(methoxymethocy)-3-nitrobenzyl bromide (28) followed by O-deprotection.On the basis of proton nuclear magnetic resonance data for the 3, 7-dialkylxanthines (3 and 9b-i) and 1, 3, 7-trialkylxanthines (5 and 14-22) thus prepared, reliable criteria for distinguishing signals of N-alkyl substituents at various positions are put forward.
从 3,7-二烷基腺嘌呤(6)[进而从 3 或 7-烷基腺嘌呤(11 或 10)]合成 3,7-二烷基黄嘌呤(9 型)的一般合成路线已经确立。该方法首先是对 1-烷基-4-(烷基氨基)-1H-咪唑-5-羧酰胺(7)进行乙氧基羰基化,通过碱性水解很容易从 6 中得到,然后在碱性条件下对得到的氨基甲酸酯(8)进行环化。在无水 K2CO3 的存在下,9 在 N,N-二甲基甲酰胺中与烷基卤化物发生烷基化反应,将上述合成路线扩展到 1,3,7-三烷基黄嘌呤水平(类型 14)。按照上述一般合成路线制备的 3-苄基-1,7-二甲基黄嘌呤(16)进行氢解去苄基化反应,可以得到副黄嘌呤(26),收率尚可。将 26 转化为 3-(4-羟基-3-硝基苄基)-1,7-二甲基黄嘌呤(24),与红藻嘌呤 phidolopin(2)是同分异构体,通过与 4-(甲氧基甲基)-3-硝基苄基溴(28)酰化,然后进行 O-脱保护。根据由此制备的 3,7-二烷基黄嘌呤(3 和 9b-i)和 1,3,7-三烷基黄嘌呤(5 和 14-22)的质子核磁共振数据,提出了区分不同位置上 N-烷基取代基信号的可靠标准。