PATHWAYS FOR THE HYDROLYSIS OF GLYCOSIDES OF N-ACETYLNEURAMINIC ACID
PATHWAYS FOR THE HYDROLYSIS OF GLYCOSIDES OF N-ACETYLNEURAMINIC ACID
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DOI：
10.1021/ja00052a011
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发表时间：
1992-12-16
影响因子：
15
通讯作者：
SINNOTT, ML
中科院分区：
文献类型：
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作者：
ASHWELL, M;GUO, XM;SINNOTT, ML
N-乙酰神经氨酸的芳基α-葡萄糖苷的水解反应可分为四个过程：（i）H_3O ~+催化的中性分子水解;（ii）H_3O ~+催化的阴离子水解（中性分子的动力学等效中性水解被小的溶剂同位素效应和接近零的β 1g值排除）;（iii）阴离子的自发水解;（iv）碱催化过程，可能涉及离子化的C9-OH在6位的亲核攻击。已经通过同位素准消旋方法测量了经历过程i-iii的对硝基苯基糖苷的二级氘动力学同位素效应（d2，pro-R和d1，pro-S，在C3; d1，在C4），其中对硝基苯基L-N-乙酰神经氨酸通过Vasella路线从L-葡萄糖制备（Helv. Chim. Acta 1986，69，1172，1191和1205）。这些效应支持这些过程的扁平C-2（5）环构象，并且对于过程ii和iii需要C1羧酸酯基团的一些亲核辅助，尽管产生了应变的α-内酯环。唾液酸酶催化和保留糖基化酶，如溶菌酶的影响进行了讨论。
The hydrolyses of aryl alpha-glucosides of N-acetylneuraminic acid proceed by four processes: (i) the H3O+-catalyzed hydrolysis of the neutral molecule; (ii) the H3O+-catalyzed hydrolysis of the anion (the kinetically equivalent neutral hydrolysis of the neutral molecule being ruled out by a small solvent isotope effect and beta1g values close to zero); (iii) the spontaneous hydrolysis of the anion; (iv) a base-catalyzed process possibly involving nucleophilic attack of the ionized C9-OH at position 6. Secondary deuterium kinetic isotope effects (d2, pro-R, and d1, pro-S, at C3; d1 at C4) have been measured for the p-nitrophenyl glycoside undergoing processes i-iii by the isotopic quasi-racemate method, with the p-nitrophenyl L-N-acetylneuraminide being made by the Vasella route from L-glucose (Helv. Chim. Acta 1986, 69, 1172, 1191, and 1205). The effects support a flattened C-2(5) ring conformation for these processes and require some nucleophilic assistance by the C1 carboxylate group for processes ii and iii, despite the strained alpha-lactone ring that results. The implications for catalysis by sialidases and retaining glycosidases such as lysozyme are discussed.