Mechanism of hydrolysis of benzoyl glucose acylals
Mechanism of hydrolysis of benzoyl glucose acylals
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苯甲酰葡萄糖缩醛的水解机理
DOI：
10.1021/ja00786a039
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发表时间：
1973
影响因子：
15
通讯作者：
T. C. Bruice
中科院分区：
文献类型：
--
作者：
Allister Brown;T. C. Bruice
研究了1 -/3-o-葡萄糖吡喃甲酰苯甲酸酯(I)、2,3 -二-0-甲基- 1 -/3- d -葡萄糖吡喃甲酰苯甲酸酯（II）和a-和/3- 2,3,4,6 -四-o-甲基-d -葡萄糖吡喃甲酰苯甲酸酯（III）在水溶液中的水解反应。在低pH和中等pH下，所有三种酯通过自发和酸催化途径水解（78）。酸催化的反应被表征为通过糖基氧碳离子进行的Al过程。现有的数据与自发水解的SnI机制一致。在高pH（30）下，观察到I和II的多相水解动力学。多相动力学解释为ho催化的O- O苯甲酰迁移与ho催化的水解竞争（方案III和方案IV）。对于I来说，O-»O苯甲酰可以从Ci迁移到Cz-OH和Ce-OH，而对于II来说，酰基只会迁移到C6-OH。在不可能发生O-* O苯甲酰迁移的fiiia， b的水解中，未观察到多相动力学，且在[HO-]中水解为一级。II和III的肼解具有亲核性和自基催化的亲核性质。当肼作为亲核试剂时，O-*·O苯甲酰基团的迁移不能与苯甲酰基团的位移竞争，并且没有观察到多相动力学。一些酶催化的糖基转移反应被认为涉及糖基酶中间体，其中糖基部分的端粒碳与羧基（糖基酰基）共价连接。一个典型的例子是大肠杆菌ß-半乳糖苷酶。3.4次级a-氘动力学同位素对水解和水解的影响程度
The hydrolysis of l-/3-o-glucopyranosyl benzoate (I), 2, 3-di-0-methyl-l-/3-D-glucopyranosyl benzoate (II), and a-and/3-2, 3, 4, 6-tetra-O-methyl-D-glucopyranosyl benzoate (III) has been studied in aqueous solution. At low and intermediate pH all three esters hydrolyze via spontaneous and acid-catalyzed paths (78). The acid-catalyzed reaction has been characterized as an Al process proceeding through a glycosyl oxocarbonium ion. The data available are consistent with an SnI mechanism for the spontaneous hydrolysis. At high pH (30) multiphasic kinetics were observed for the hydrolysis of I and II. The multiphasic kinetics were interpreted in terms of HO-catalyzed O— O benzoyl migration in competition with HO-catalyzed hydrolysis (Schemes III and IV). For I, O-» O benzoyl migration may occur from Ci to Cz-OH and Ce-OH while for II acyl migration may only occur to C6-OH. In the hydrolysis ofIIIa, b where O-* O benzoyl migration is not possible, multiphasic kinetics are not observed and hydrolysis is first order in [HO-]. Hydrazinolysis of II and III is both nucleophilic and selfgeneral-base catalyzed nucleophilicin nature. When hydrazine serves as a nucleophile, O-*· O benzoyl groupmigration cannot compete with the displacement of the benzoyl group and multiphasic kinetics are not observed.Anumber of enzyme-catalyzed glycosyl transfer re-actions have been suggestedto involve glycosyl enzyme intermediatesin which the anomeric carbon of the glycosyl moiety is covalently linked to a carboxyl group (a glycosyl acylal). 2 A case in point is E. coli ß-galactosidase. 3· 4 The magnitude of the secondary a-deuterium kinetic isotope effects for hydrolysis and