MECHANISMS OF PRIMARY ACID MODIFICATION REACTION OF REDUCED DIPHOSPHOPYRIDINE NUCLEOTIDE MODELS
MECHANISMS OF PRIMARY ACID MODIFICATION REACTION OF REDUCED DIPHOSPHOPYRIDINE NUCLEOTIDE MODELS
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DOI：
10.1021/bi00846a041
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发表时间：
1968-01-01
期刊：
影响因子：
2.9
通讯作者：
CHAYKIN, S
中科院分区：
文献类型：
--
作者：
KIM, CSY;CHAYKIN, S
研究了还原二磷酸吡啶核苷酸（DPNH）模型化合物的初级酸修饰反应。l-（2,6-二氯苯基）- 1,4 -二氢烟酰胺(S)在pH为5的四氢呋喃-水（40:60）中反应得到结晶酸产物（S[长冲线]H2O），产率高。S[长划]H2O通过x射线晶体学鉴定为1-（2,6-二氯苯基）-6-羟基-1,4,5,6-四氢烟酰胺。对S[长划]H2O的核磁共振谱的独立分析得出了同样的结论。采用分光光度法和同位素速率效应技术对反应机理进行了动力学分析。反应分两个步骤进行，首先在烟酰胺环的C-5位置进行亲化，然后在C-6位置进行羟基化。该反应为二级反应(速率= k(H+)(S))，表明只有1个步骤是控制速率的。在水条件下，当使用氚或氘时，反应表现出很强的同位素效应（37[度]时kH/kT = 10, 11[度]时kH/kT = 17），表明质子化是速率决定步骤。然而，在基本无水的条件下（含约1% H2O的四氢呋喃或二氧六烷），反应没有表现出同位素效应，表明羟基化是速率决定步骤。通过分光光度法和测定回收物中氚的掺入度，证明了第一步是可逆的。将S[长划]H2O置于无水有机介质中，观察S的特征吸收带（[lambda] max 350 m[mu]）的出现和水的形成（通过核磁共振波谱法），证明了反应的总体可逆性。
The primary acid modification reaction of a reduced diphosphopyridine nucleotide (DPNH) model compound was studied. l-(2,6-Dichlorobenzyl)-l,4-dihydronicotinamide (S) underwent reaction at pH 5 in tetrahydrofuran-water (40:60) to give a crystalline acid product (S[long dash]H2O) in a good yield. S[long dash]H2O was identified as 1-(2,6-dichlorobenzyl)-6-hydroxy-1,4,5,6-tetrahydronicotinamide by X-ray crystallography. An independent analysis of the nuclear magnetic resonance spectrum of S[long dash]H2O led to the same conclusion. Kinetic analysis of the reaction mechanism was carried out using both spectrophotometric and isotopic rate effect techniques. The reaction proceeded in 2 steps, with initial pro-tonation at the C-5 position of the nicotinamide ring and subsequent hydroxylation at the C-6 position. The reaction was 2nd order (rate = k(H+)(S)), indicating that only 1 of the steps was rate controlling. Under aqueous conditions the reaction showed a strong isotope effect when tritium or deuterium was used (kH/kT = 10 at 37[degree]and 17 at 11[degree]), indicating that protonation was the rate-determining step. However, under substantially anhydrous conditions (tetrahydrofuran or dioxane containing about 1% H2O), the reaction showed no isotope effect, indicating that hydroxylation was the rate-determining step. The 1st step was shown to be reversible lay a spectrophotometric method and by determination of the degree of tritium incorporation in the recovered reactant. The over-all reversibility of the reaction was demonstrated by subjecting S[long dash]H2O to an anhydrous organic medium and observing the appearance of the characteristic absorption band of S ([lambda] max 350 m[mu]) and the formation of water (by nuclear magnetic resonance spectroscopy).