Lönnberg H, Lehikoinen P
Nucleic Acids Res. 1982 Jul 24;10(14):4339-49. doi: 10.1093/nar/10.14.4339.
The pH-rate profiles were determined for the acidic hydrolysis of some 6-substituted 9-(beta-D-ribofuranosyl) purines. The product analyses indicated that the reactions generally proceed with formation of purine bases as initial products. However, at low oxonium ion concentrations the hydrolysis of the unsubstituted compound yields 4-amino-5-formamidopyrimidine, instead of purine formed in highly acidic solutions. The rate constants for the spontaneous and oxonium ion catalyzed heterolysis of the protonated substrates were calculated from the acidity constants and the observed rate constants. The dependence of the partial rate constants on the polar nature of the 6-substituents are consistent with rate-limiting formation of free purine bases and glycosyl oxocarbenium ions. No anomerization of the substrates was observed during the course of the hydrolysis.
测定了一些6-取代的9-(β-D-呋喃核糖基)嘌呤的酸性水解反应的pH-速率曲线。产物分析表明，这些反应通常首先生成嘌呤碱。然而，在低氧鎓离子浓度下，未取代化合物的水解产生4-氨基-5-甲酰胺基嘧啶，而不是在高酸性溶液中形成的嘌呤。根据酸度常数和观察到的速率常数计算了质子化底物的自发和氧鎓离子催化异裂的速率常数。部分速率常数对6-取代基极性的依赖性与游离嘌呤碱和糖基氧碳鎓离子的限速形成一致。在水解过程中未观察到底物的异头化现象。
