O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Platinum(IV) Chloride as a Dual Catalyst Permitting Stereo- and Regioselective Glycosidations
O-Glycosyl Trichloroacetimidates as Glycosyl Donors and Platinum(IV) Chloride as a Dual Catalyst Permitting Stereo- and Regioselective Glycosidations
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DOI：
10.1021/acscatal.1c02256
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发表时间：
2021-08
期刊：
影响因子：
12.9
通讯作者：
Tong Li;Tianlu Li;Haoru Zhuang;Fengshan Wang;R. Schmidt;Peng Peng-Peng
中科院分区：
文献类型：
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作者：
Tong Li;Tianlu Li;Haoru Zhuang;Fengshan Wang;R. Schmidt;Peng Peng-Peng
立体选择性和区域选择性糖苷化反应仍然是碳水化合物化学中的一个巨大挑战。在这一领域的巨大努力中，可用于O-糖基三氯乙酰亚胺酯活化的酸碱催化特别令人感兴趣。其特征在于通过催化剂与糖基受体之间的顺序结合，然后与糖基供体之间的顺序结合引发的替代糖苷化途径。通过形成催化剂-受体加合物，达到增加的质子酸性和氧亲核性，从而加强供体活化和伴随的受体转移。由于反应通过SN 2型过渡态发生，因此基本上具有立体选择性。氯化铂（IV）在这方面是一种理想的催化剂;它是一种弱刘易斯酸，但由于其配体结合能力，它对糖基受体羟基具有高亲和力，从而从α-构型的糖基供体提供主要为β-构型的糖苷化产物。此外，氯化铂（IV）进行双齿连接的能力是另一个优点，因为它增强了羟基之间的亲核性差异，从而允许区域选择性糖苷化，如对碳水化合物受体中存在的各种1，2-顺式-、1，3-和1，2-反式-二醇和1，2，3-三醇部分所观察到的。这一观察结果可用于有效的皂苷天然产物合成。
Stereo- and regioselective glycosidation is still a great challenge in carbohydrate chemistry. Among the tremendous endeavors in this area, acid–base catalysis, available toO-glycosyl trichloroacetimidate activation, is of particular interest. It features an alternative glycosidation pathway initiated by the sequential binding between the catalyst and the glycosyl acceptor and then with the glycosyl donor. Through the formation of a catalyst–acceptor adduct, increased proton acidity and oxygen nucleophilicity are reached, thus enforcing donor activation and concomitant acceptor transfer. As the reaction takes place via an SN2-type transition state, essentially stereoselectivity is granted. Platinum(IV) chloride is an ideal catalyst in this regard; it is a weak Lewis acid, yet it possesses high affinity to the glycosyl acceptor hydroxy group due to its ligand-binding capacity, thus affording from the α-configurated glycosyl donor the glycosidation product predominantly in β-configuration. In addition, the capacity of platinum(IV) chloride to bidentate ligation is another advantage, as it enhances nucleophilicity differences between hydroxy groups, thus permitting regioselective glycosidation, as observed for various 1,2-cis-, 1,3-, and 1,2-trans-diol and 1,2,3-triol moieties present in carbohydrate acceptors. This observation found application in an efficient saponin natural product synthesis.