Purines. XXIX. Syntheses of 9-alkyl-2-deuterio-N6-methoxyadenines and 2-deuterio-N6,9-dimethyladenine: Tautomerism in 9-substituted N6-alkoxyadenines.
作者:TOZO FUJII、TOHRU SAITO、TAISUKE ITAYA、KYOKO KIZU、YUKINARI KUMAZAWA、SATOSHI NAKAJIMA
DOI:10.1248/cpb.35.4482
日期:——
Cyclizations of the alkoxyamidines 7a, i with formic acid gave N6-methoxy-9-methyladenine (8a) and 9-benzyl-N6-methoxyadenine (8i). Replacement of formic acid by formic-d acid-d in these cyclizations afforded the 2-deuterated species 13a and 13i. A similar cyclization of 22, obtained from 21 by alkaline hydrolysis, with formic-d acid-d yielded 2-deuterio-N6-methoxy-1, 9-dimethyladenine (24). The N6-methyl isomer 19 was prepared from 13a by treatment with NaH and MeI. Comparison of the proton nuclear magnetic resonance (1H-NMR) spectrum of 8a in Me2SO-d6 with that of 13a revealed that 8a exists as an equilibrated 1 : 3.5 mixture of the amino (type 14 or 15) and the imino (type 16 or 17) forms. The deuterated species 19 and 24 were utilized for interpretation of the 1H-NMR spectra of the amino-form model 18 and the imino-form model 23. The existence of amino-imino tautomerism in 8a was also supported by ultraviolet and infrared spectroscopic evidence. Such tautomerism, with a preference for the imino form, in Me2SO-d6 was found to be common to 13 other 9-substituted N6-alkoxyadenines (type 8) including adenosine analogues. On the other hand, comparison of the 1H-NMR spectra of 11, N6, 9-dimethyladenine (12), and N6, N6, 9-trimethyladenine (36) indicated that 12 exists solely in the amino form in CDCl3 or Me2SO-d6.
烷氧基脒7a、7i与甲酸的环化反应分别得到了N6-甲氧基-9-甲基腺嘌呤(8a)和9-苄基-N6-甲氧基腺嘌呤(8i)。在这些环化反应中,用重氢甲酸(formic-d酸-d)替代甲酸得到了2-氘化的物种13a和13i。类似地,从21通过碱水解获得的22与重氢甲酸的环化反应得到了2-氘代-N6-甲氧基-1,9-二甲基腺嘌呤(24)。N6-甲基异构体19是通过NaH和MeI处理13a制备的。8a在二甲亚砜-d6中的质子核磁共振(1H-NMR)谱与13a的谱图对比显示,8a以1:3.5的比例平衡存在氨基(类型14或15)和亚氨基(类型16或17)形式。氘代物种19和24用于解释氨基形式模型18和亚氨基形式模型23的1H-NMR谱图。8a中存在的氨基-亚氨基互变异构现象也得到了紫外和红外光谱证据的支持。这种在二甲亚砜-d6中偏好亚氨基形式的互变异构现象在其他13种9-取代的N6-烷氧基腺嘌呤(类型8)中普遍存在,包括腺苷类似物。另一方面,N6,9-二甲基腺嘌呤(12)和N6,N6,9-三甲基腺嘌呤(36)的1H-NMR谱图对比表明,12在CDCl3或二甲亚砜-d6中仅以氨基形式存在。