Why Is Direct Glycosylation with N-Acetylglucosamine Donors Such a Poor Reaction and What Can Be Done about It?

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• 作者：Mikkel H. S. Marqvorsen ; Martin J. Pedersen ; Michelle R. Rasmussen ; Steffan K. Kristensen ; Rasmus Dahl-Lassen ; Henrik H. Jensen
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：January 6, 2017
• 年：2017
• 卷：82
• 期：1
• 页码：143-156
• 全文大小：734K
• ISSN：1520-6904

文摘

The monosaccharide N-acetyl-n class="smallcaps">dn>-glucosamine (GlcNAc) is an abundant building block in naturally occurring oligosaccharides, but its incorporation by chemical glycosylation is challenging since direct reactions are low yielding. This issue, generally agreed upon to be caused by an intermediate 1,2-oxazoline, is often bypassed by introducing extra synthetic steps to avoid the presence of the NHAc functional group during glycosylation. The present paper describes new fundamental mechanistic insights into the inherent challenges of performing direct glycosylation with GlcNAc. These results show that controlling the balance of oxazoline formation and glycosylation is key to achieving acceptable chemical yields. By applying this line of reasoning to direct glycosylation with a traditional thioglycoside donor of GlcNAc, which otherwise affords poor glycosylation yields, one may obtain useful glycosylation results.