Selectivity Switch in the Catalytic Functionalization of Nonprotected Carbohydrates: Selective Synthesis in the Presence of Anomeric and Structurally Similar Carbohydrates under Mild Conditions ■ Results and Discussion
Selectivity Switch in the Catalytic Functionalization of Nonprotected Carbohydrates: Selective Synthesis in the Presence of Anomeric and Structurally Similar Carbohydrates under Mild Conditions ■ Results and Discussion
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通讯作者：
Wataru Muramatsu;Y. Takemoto
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作者：
Wataru Muramatsu;Y. Takemoto
A catalytic process for the chemo-and regioselective functionalization of nonprotected carbohydrates has been developed. This novel process allows selective thiocarbonylation, acylation, and sulfonylation of a particular hydroxy group in a particular carbohydrate in the simultaneous presence of structurally similar carbohydrates such as anomers. In addition, the chemoselectivity can be switched by regulating only the length of the alkyl chain in the organotin catalyst. ■ INTRODUCTION Carbohydrates including oligosaccharides and glycoconjugates have been known to play crucial roles in various physiologic and pathologic events such as cell adhesion, fertilization, and cancer cell metastases. 1 With the aim to gain insight into the mechanism of these events and to develop new medicines, the development of efficient routes and comprehensive procedures for the high purity synthesis of such carbohydrates is indispensable. In the past years, various methods for stereo-and regioselective synthesis of carbohydrates have been developed. 2 However, these methods do not necessarily afford high stereo-and regioselectivity to all the substrates, and subsequent separation of anomers by simple methods such as silica gel column chromatography and recrystallization is generally very difficult as anomers often have similar polarity and solubility properties. In addition, special instrument techniques such as high-performance liquid chromatography (HPLC) are unsuitable for the fast separation of a large quantity of anomers. Therefore, effort-consuming derivatization of anomers with multistep protection−deprotection sequences has been often attempted for separation of anomers. To resolve such problems, enzymatic method for the separation of an anomeric mixture of carbohydrates and structurally similar carbohydrates has been developed in the last few decades. 3 For example, Gotor and co-workers reported the separation method of an anomeric mixture of α-and β-D-nucleosides through regioselective lipase-catalyzed acylation. 3d More recently, Prasad and co-workers reported the separation method of a mixture of furanosyl and pyranosyl nucleosides through chemo-and regioselective lipase-catalyzed acylation. 3e These catalyses are useful techniques for the separation with protection (acyl) group in a minimum number of steps. However, the resulting functionalized nucleosides and carbohydrates are usually not the ideal precursors for further functionalization. To the best of our knowledge, on the other hand, a nonenzymatic method has not been reported to date. Herein, we present research to facilitate chemical functionalization and separation of carbohydrates utilizing the high molecular recognition ability of organotin catalysts. In the last a few years, we have investigated a catalytic method for the regioselective introduction of useful functional groups into nonprotected carbohydrates. 2j,4 In these results, …
