A Comparative Study of Glycosyl Thioimidates as Building Blocks for Chemical Glycosylation

Abstract

Our results indicate that the reactivity and the activation profile of thioimidate glycosyl donors vary significantly depending on the endocyclic heteroatom (N,O,S). Reactivity diminishes in accordance with the following sequence: O > S > N; and this trend stands for a majority of promoters tested. Acyclic glycosyl thioimidates were found to be generally less reactive than the respective cyclic counterparts. The difference in the reactivity was confirmed in direct competition experiments. These findings made possible a two-step one-pot selective activation using thioimidates as the anomeric leaving group of the glycosyl donor and temporary masking group of the glycosyl acceptor.

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Keywords:

• Glycosylation
• Thioimidates
• Carbohydrates
• Oligosaccharides

ACKNOWLEDGMENTS

The authors thank the National Science Foundation (Award CHE-1058112) and the National Institute of General Medical Studies (Award GM077170) for providing generous support for this work. SJH is indebted to the UMSL Graduate School for awarding him with the Dissertation Fellowship.