Stereoselective Synthesis of 2-C-Branched (Acetylmethyl) Oligosaccharides and Glycoconjugates: Lewis Acid-Catalyzed Glycosylation from 1,2-Cyclopropaneacetylated Sugars

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• 作者：Qiang Tian ; Liang Dong ; Xiaofeng Ma ; Liyan Xu ; Changwei Hu ; Wei Zou ; Huawu Shao
• 刊名：Journal of Organic Chemistry
• 出版年：2011
• 出版时间：February 18, 2011
• 年：2011
• 卷：76
• 期：4
• 页码：1045-1053
• 全文大小：1042K
• 年卷期：v.76,no.4(February 18, 2011)
• ISSN：1520-6904

文摘

1,2-Cyclopropaneacetylated sugars as glycosyl donors reacted with a series of glycosyl acceptors (monosaccharides, amino acids, and other alcohols) in the presence of Lewis acid to produce oligosaccharides and glycoconjugates containing 2-C-acetylmethylsugars. Galactosyl donor gave good to excellent 伪-selectivities with TMSOTf as a catalyst, whereas galactosyl donor offered moderate to good 尾-selectivities when BF₃路Et₂O was used as a catalyst. However, glucosyl donors produced 尾-exclusive selectivity under both conditions. The stereoselectivities of glycosylation depend on the reactivity of donor sugars and Lewis acid catalyst, which effectively dictated the glycosylation pathways. The evidence suggests that galactosyl donors (e.g., 7) can undergo S_N1 pathway with a strong Lewis acid (TMSOTf) and S_N2 pathway under BF₃路Et₂O, whereas the glucosyl donors (e.g., 8 and 10) followed S_N2 pathway. The stereoselectivity was also consequential to the formation of a C2鈥?acetal intermediate formed via the 2-C-acetylmethyl group and the anomeric carbonium intermediate in glycosylation.