Mechanistic studies on the stereoselective formation of glycosyl iodides: First characterization of beta-D-glycosyl iodides
Mechanistic studies on the stereoselective formation of glycosyl iodides: First characterization of beta-D-glycosyl iodides
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DOI：
10.1016/s0008-6215(96)00321-7
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发表时间：
1997-05-12
影响因子：
3.1
通讯作者：
Hadd, MJ
中科院分区：
文献类型：
--
作者：
Gervay, J;Nguyen, TN;Hadd, MJ
糖基乙酸酯与一个当量的碘三甲基硅烷在低温下处理导致糖基碘的定量形成。在C-2位具有参与基团的碳水化合物最初形成β-D-糖基碘，它很快与α-碘异构体平衡。过乙酰化葡萄糖的β异构体比α异构体反应更快，这可能是因为C-2醋酸酯可以帮助取代硅基化的异构体醋酸酯。相反，在缺乏C-2参与基团的底物中，α异构体的反应速度快于β异构体。例如，1-O-acetyl-2，3，4，6-tetra-O-benzyl-alpha-D-glucopyranose的激活会导致形成β-碘，而相应的β-乙酸酯则会产生α-碘。尽管β-碘化物与α-异构体迅速平衡，但它们可以在平衡缓慢的低温下大量制备。本报告首次报道了P-D-糖基碘的立体选择性形成和表征。(C)1997年爱思唯尔科学有限公司。
Treatment of glycosyl acetates with one equivalent of iodotrimethylsilane at low temperature results in the quantitative formation of glycosyl iodides. Carbohydrates that possess a participating group at the C-2 position initially form beta-D-glycosyl iodides, which quickly equilibrate to the alpha-iodo anomers. The beta anomer of peracetylated glucose reacts faster than the alpha anomer, presumably because the C-2 acetate can assist in displacing the silylated anomeric acetate. In contrast, the alpha anomer reacts faster than the beta anomer in substrates lacking a participating group at C-2. For example, activation of 1-O-acetyl-2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranose leads to formation of the beta iodide, while the corresponding beta acetate produces the alpha iodide. Although the beta iodides quickly equilibrate to the alpha anomers, they can be prepared in sizable quantities at low temperatures where equilibration is slow. This report describes the first stereoselective formation and characterization of P-D-glycosyl iodides. (C) 1997 Elsevier Science Ltd.