"Super armed" glycosyl donors: Conformational arming of thioglycosides by silylation
"Super armed" glycosyl donors: Conformational arming of thioglycosides by silylation
复制标题
DOI：
10.1021/ja071955l
复制
发表时间：
2007-07-25
影响因子：
15
通讯作者：
Bols, Mikael
中科院分区：
文献类型：
--
作者：
Pedersen, Christian Marcus;Nordstrom, Lars Ulrik;Bols, Mikael
在2 -、3 -和4 - OH基团上被大体积硅基保护基（叔丁基二甲基硅基，TBS）保护的糖基供体被发现与苄基化硫代葡萄糖苷相比具有更高的反应活性。这种增强的反应活性是由硅基化诱导的构象变化相关的立体电子效应所解释。一个TBS硅基化的硫代葡萄糖苷供体具有轴向的OR基团，而一个苄基化的硫代葡萄糖苷具有平伏的OR基团，这导致在过渡态中有更有利的电荷 - 偶极相互作用。这个概念可用于创建“超强活化”的葡萄糖基、甘露糖基、鼠李糖基和半乳糖基供体，它们可与活化受体苯基2,3,4 - 三 - O - 苄基 - β - D - 硫代葡萄糖苷或苯基2,3,6 - 三 - O - 苄基 - β - D - 硫代葡萄糖苷交叉偶联，以良好至优异的产率得到相应的活化二糖。
Glycosyl donors protected with bulky silyl protective groups (tert-butyldimethylsilyl, TBS), on the 2-, 3-, and 4-OH groups were found to have superior reactivity compared with benzylated thioglucosides. The enhanced reactivity is explained by the stereoelectronic effects associated with the conformational change induced by the silylation. A TBS silylated thioglucoside donor has axial OR groups, whereas a benzylated thioglucoside has equatorial OR groups, leading to much more favorable charge-dipole interactions in the transition state. This concept could be used to create "super armed" glucosyl, mannosyl, rhamnosyl, and galactosyl donors, which could cross-couple with the armed acceptors, phenyl 2,3,4-tri-O- benzyl-beta-D-thioglucoside or phenyl 2,3,6-tri-O-benzyl-beta-D-thioglucoside, to give the corresponding armed disaccharides in good to excellent yields.