In order to investigate the effects of the N(3)- and N(9)-substituents in 3, 9-disubstituted adenines on the stability of the adenine ring, the equilibrium constants and the rates of ring opening and cyclization for the equilibria between the 3, 9-disubstituted adenines IVa-l and the N-alkylformamidoimidazoles Va-l in H2O at pH 8.98 and 25 °C have been measured. A bulky substituent at the 3-position of IV has been found to retard the ring opening leading to V, whereas an electron-withdrawing group at the 3- or 9-position accelerates it. A bulky alkyl group on the formamido nitrogen of V markedly retards the cyclization leading to IV, favoring the ring-opened form in the equilibrated mixture. Syntheses of 3-isopropyl-9-methyladenine perchlorate (IVc) and 3-(4-methoxybenzyl)-9-methyladenine perchlorate (IVe), required for the kinetic study as substrates, are also described.
为了研究 3、9-二取代
腺嘌呤中的 N(3)-和 N(9)-取代基对
腺嘌呤环稳定性的影响,我们测量了 3、9-二取代
腺嘌呤 IVa-l 和 N-烷基甲
酰胺基
咪唑 Va-l 在 pH 值为 8.98 和 25 ℃ 的
H2O 中的平衡常数以及开环和环化速率。研究发现,IV 的 3 位上的一个大取代基会延缓 V 的开环,而 3 位或 9 位上的一个抽电子基则会加速 V 的开环。在 V 的甲酰
氨基
氮上的一个大烷基明显延缓了 IV 的环化,有利于平衡混合物中的开环形式。此外,还介绍了 3-
异丙基-
9-甲基腺嘌呤高氯酸盐(IVc)和 3-(
4-甲氧基苄基)-
9-甲基腺嘌呤高氯酸盐(IVe)的合成过程。