1,2-环丙烷乙酰化糖水解机理的理论研究

Theoretical investigation on mechanism of hydrolysis of 1,2-cyclopropaneacetylated sugar

采用密度泛函B3LYP方法研究了1,2-环丙烷乙酰化糖在氘代氯仿溶液中的水解反应的详细机理。计算结果表明,当H2O分子从不同方向进攻1,2-环丙烷乙酰化糖分子时,会形成不同的反应途径,当H2O从糖分子的六元环平面下方进攻时,反应为一步反应,环丙烷的开环步骤为反应决速步,生成α构型产物。当H2O从糖分子的六元环平面上方进攻时,反应为两步反应,形成产物的氢迁移步骤为决速步,生成β构型产物。H2O从糖分子平面下方进攻的反应途径在热力学及动力学上都更有优势,1,2-环丙烷乙酰化糖的水解反应更有利于生成α构型产物,计算结果与实验结果一致。

The mechanism of the hydrolysis of 1,2-cyclopropaneacetylated sugar in CDCl3 was investigated in detail using the B3LYP method. The computational results indicated that H2 O could attack 1,2-cyclopropaneacetylated sugar from two directions, therefore two paths are obtained. When H2 O attacks the three-membered ring of the cyclopropane from below the surface of the six-membered ring of the sugar（ path A） ,the reaction is one-step reaction and the α-configuration product is obtained. The step of the cyclopropane ring opening on the sugar is the rate-determining step（RDS）. When H2O attacks the three-membered ring of the cy-clopropane from above the surface of the six-membered ring of the sugar（ path B） ,the reaction is composed of two steps and theβ-configuration product is obtained. The hydrogen migration step is the RDS. Path A is predicted to be more kinetically and thermody-namically favored in CDCl3 than path B. The major product is in α-configuration and the results are in agreement with the experi-mental observations.