CHARGE DESCRIPTION OF BASE-CATALYZED ALCOHOLYSIS OF ARYL PHOSPHODIESTERS - A RIBONUCLEASE MODEL
CHARGE DESCRIPTION OF BASE-CATALYZED ALCOHOLYSIS OF ARYL PHOSPHODIESTERS - A RIBONUCLEASE MODEL
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DOI：
10.1021/ja00223a031
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发表时间：
1988-07-20
影响因子：
15
通讯作者：
WILLIAMS, A
中科院分区：
文献类型：
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作者：
DAVIS, AM;HALL, AD;WILLIAMS, A
取代苯酚从芳基尿苷-3“-磷酸的释放由碱基催化，并涉及环化以形成2”，3“-环核苷酸。咪唑和氢氧根离子催化的速率常数（分别为kim和kOH）遵循Br vnsted方程（25 ℃和0.25M离子强度）log kim = -0.59 pKArOH + 1.40（n = 7，r = 0.955）和log kOH = -0.54 pKArOH + 6.68（n = 9，r = 0.967）。一般碱催化4-硝基苯酚从4-硝基苯酯（kB）中释放符合Br.vphi.nsted关系log kB = 0.67 pKBH - 7.50（n = 7，r = 0.989）。碱和离去基团原子上的电荷变化由相应的β确定。并且β EQ值不平衡。与文献中数据的比较表明，电荷的差异可能归因于进攻氧（2 ″-羟基）而不是O ↑ [2]中的磷酰氧。cntdot.. cntdot.PO2.cntdot.. cntdot.. cntdot.原子群。认为反应的P2 O键形成和键分裂组分在位于协调路径上的过渡态中仅微弱地进行。
The release of substituted phenol from aryl uridine-3''-phosphates is catalyzed by bases and involves cyclization to form the 2'',3''-cyclic nucleotide. The rate constants for imidazole and hydroxide ion catalysis (kim and kOH, respectively) obey the Br.vphi.nsted equations (25.degree.C and 0.25 M ionic strength) log kim = -0.59 pKArOH + 1.40 (n = 7, r = 0.955) and log kOH = -0.54 pKArOH + 6.68 (n = 9, r = 0.967). General-base-catalyzed release of 4-nitrophenol from the 4-nitrophenyl ester (kB) obeys the Br.vphi.nsted relationship log kB = 0.67 pKBH - 7.50 (n = 7, r = 0.989). Charge changes on base and leaving group atoms as determined from the corresponding .beta. and .beta.eq values do not balance. Comparison with data in the literature indicates that the difference in charge may be assigned to the attacking oxygen (2''-hydroxyl) rather than to the phosphoryl oxygens in the O.cntdot..cntdot..cntdot.PO2.cntdot..cntdot..cntdot. group of atoms. both P.sbd.O bond forming and bond fission components of the reaction are considered to be only weakly advanced in a transition state that lies on a concerted pathway.