Department of Biological Science & Technology, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan.
Carbohydr Res. 2011 Oct 18;346(14):2098-103. doi: 10.1016/j.carres.2011.06.026. Epub 2011 Jun 29.
Highly diastereoselective glycosylation reactions have been developed; however, not all glycosylation reactions are diastereoselective and these reactions have probably not been reported. For some fucosylation reactions, unusually low or abnormally opposite selectivities have been demonstrated. In the present study, the fucosylation reaction of long-chain hydrocarbon alcohols, ethyl 9-hydroxynonanoate and decanol using a series of the 2-O-benzyl-protected fucopyranosyl donors were investigated. The resulting products demonstrated the solvent-induced diastereoselectivity switching using diethyl ether (Et(2)O) or dichloromethane (CH(2)Cl(2)). Practical α-selectivities were observed using ether solvents. In contrast, practical β-selectivities were observed using CH(2)Cl(2). The anomeric diastereoselectivity switching was similarly observed in the alcohol galactosylation reaction. The larger spin-lattice relaxation time constant (T(1)) actually indicated that molecular motion of ethyl 9-hydroxynonanoate was more vigorous in Et(2)O than in CH(2)Cl(2), suggesting its dissociation in Et(2)O and association in CH(2)Cl(2). The bulkiness of the associated alcohols is most likely responsible for the observed diastereoselectivity.
已开发出高度非对映选择性的糖苷化反应；然而，并非所有的糖苷化反应都是非对映选择性的，并且这些反应可能尚未被报道。对于一些岩藻糖基化反应，已经证明了异常低或异常相反的选择性。在本研究中，使用一系列 2-O-苄基保护的岩藻糖基供体，研究了长链烃醇，乙基 9-羟基壬酸酯和癸醇的岩藻糖基化反应。所得产物表现出使用二乙醚（Et（2）O）或二氯甲烷（CH（2）Cl（2））的溶剂诱导的非对映选择性切换。使用醚溶剂观察到实际的α选择性。相比之下，使用 CH（2）Cl（2）观察到实际的β选择性。在醇半乳糖基化反应中也观察到类似的端基非对映选择性切换。较大的自旋晶格弛豫时间常数（T（1））实际上表明，乙基 9-羟基壬酸酯在 Et（2）O 中的分子运动比在 CH（2）Cl（2）中更为剧烈，表明其在 Et（2）O 中解离，在 CH（2）Cl（2）中缔合。缔合醇的体积可能是导致观察到的非对映选择性的原因。
