Acceleration and Deceleration Factors on the Hydrolysis Reaction of 4,6-O-Benzylidene Acetal Group
Acceleration and Deceleration Factors on the Hydrolysis Reaction of 4,6-O-Benzylidene Acetal Group
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DOI：
10.1021/acs.joc.0c00395
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发表时间：
2020-12-18
影响因子：
3.6
通讯作者：
Kajihara, Yasuhiro
中科院分区：
文献类型：
--
作者：
Maki, Yuta;Nomura, Kota;Kajihara, Yasuhiro
亚甲基缩醛不仅是碳水化合物化学中最重要的保护基团之一，而且在一般有机化学中也是最重要的保护基之一。对于4，6-O-亚苄基糖苷，我们以前发现，4位上的立体化学改变了亚甲基缩醛基团的反应速率常数。然而，加速或减速系数的细节仍不清楚。本工作利用Arrhenius和Eyring图分析了亚甲基缩醛基团的水解反应，得到了糖苷(GLC)、甘露糖苷(Man)和半乳糖苷(Gal)的单独参数。Arrhenius和Eyring作图表明，指前因子(A)和Delta S双匕首是Gal在非乙酰化底物中最小反应速率常数的关键。E-a/Delta H双匕首和A/Delta S双匕首对双乙酰底物中半乳糖的最小反应速率常数均有影响。所有参数表明，水合反应的速率常数受质子化和水合步骤以及溶剂化的调节。所得到的参数支持亚苄缩亚基通过亚甲缩醛的快速水解作为顺式和反式稠合双环体系的正交性保护。
The benzylidene acetal group is one of the most important protecting groups not only in carbohydrate chemistry but also in general organic chemistry. In the case of 4,6-O-benzylidene glycosides, we previously found that the stereochemistry at 4-position altered the reaction rate constant for hydrolysis of benzylidene acetal group. However, a detail of the acceleration or deceleration factor was still unclear. In this work, the hydrolysis reaction of benzylidene acetal group was analyzed using the Arrhenius and Eyring plot to obtain individual parameters for glucosides (Glc), mannosides (Man), and galactosides (Gal). The Arrhenius and Eyring plot indicated that the pre-exponential factor (A) and Delta S double dagger were critical for the smallest reaction rate constant of Gal among nonacetylated substrates. On the other hand, both E-a/Delta H double dagger and A/Delta S double dagger were influential for the smallest reaction rate constant of Gal among diacetylated substrates. All parameters obtained suggested that the rate constant for hydrolysis reaction was regulated by protonation and hydration steps along with solvation. The obtained parameters support wide use of benzylidene acetal group as orthogonal protection of cis- and trans-fused bicyclic systems through the fast hydrolysis of the trans-fused benzylidene acetal group.