Observations on the activation of methyl thioglycosides by iodine and its interhalogen compounds
作者:K.P.Ravindranathan Kartha、Peter Cura、Mahmoud Aloui、S.Kristy Readman、Trevor J Rutherford、Robert A Field
DOI:10.1016/s0957-4166(99)00501-7
日期:2000.2
to be intermolecular, whereas the latter iodine–hexamethyldisilane-promoted epimerisation is intramolecular. Treatment of the same methyl thiogalactosides with iodine monobromide gives rise to the thermodynamically favoured α-glycosyl bromides, whereas reaction with iodine monochloride initially gives the kinetic β-glycosyl chlorides, which slowly epimerise to the thermodynamic α-linked products. Differences
在没有受体醇的情况下用碘处理“武装”的甲基硫代半乳糖苷会导致巯基糖苷差向异构化,而对相应的“解除武装”的甲基硫代糖苷没有影响。相比之下,碘-六甲基乙硅烷(原位生成碘三甲基硅烷)引起“解除武装”的硫代糖苷的差向异构化,最终在延长的暴露时间产生相应的α-糖基碘化物。交叉实验表明,前者由碘促进的差向异构化是分子间的,而后者由碘-六甲基乙硅烷促进的差向异构化是分子内的。用一溴化碘处理相同的甲基硫代半乳糖苷会产生热力学上有利的α-糖基溴化物,而与一氯化碘的反应最初会生成动力学的β-糖基氯化物,慢慢地向热力学α-连接产物中差向异构化。I–I,I–Br和I–Cl激活硫糖苷的结果不同,这表明通过精心选择启动子可能会影响基于硫糖苷的糖基化反应的立体化学过程。