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This chapter begins with an account of the serendipitous events that led to the development of n-pentenyl glycosides (NPGs) as glycosyl donors, followed by the chance events that laid the foundation for the armed–disarmed strategy for oligosaccharide assembly. A key mechanistic issue for this strategy was that, although both armed and disarmed entities could function independently as glycosyl donors,...
This chapter summarizes the concepts and chemistry developed by Ley’s group in relation to the relevance of reactivity tuning in oligosaccharide coupling reactions. The recognition that protecting groups affect the reactivity of glycosyl donors allowed Ley’s group to make imaginative use of their 1,2-diacetal protecting groups. The combination of 1,2-diacetals with the presence of different anomeric...
The fine tuning of thioglycosides used as glycosyl donors occurs through careful manipulations of the aglycon’s nucleofugality, for example, by using “active–latent” principles. In the first section, the control of the relative leaving group abilities will be discussed in terms of electronic factors, including electron-donating/withdrawing substituents. In the second section, the nucleofugality will...
Here we review the equatorial β-directing effects of electron-withdrawing protecting groups at remote positions of mannopyranosyl donors, mannuronate donors, rhamnopyranosyl donors, and 2,6-dideoxyglucopyranosyl donors. We discuss the equatorial α-directing effect of an electron-withdrawing group at the N-5 position of sialyl donors. The proposed mechanism and origin of some of the equatorial β-directing...
The genesis and development of the 4,6-O-benzylidene acetal method for the preparation of β-mannopyranosides are reviewed. Particular emphasis is placed on the influence of the various protecting groups on stereoselectivity and these effects are interpreted in the framework of a general mechanistic scheme invoking a series of solvent-separated and contact ion pairs in dynamic equilibrium with a covalent...
Traditional strategies for oligosaccharide synthesis often require extensive protecting and/or leaving group manipulations between each glycosylation step, thereby increasing the total number of synthetic steps while decreasing both the efficiency and yield. In contrast, expeditious strategies allow for the rapid chemical synthesis of complex carbohydrates by minimizing extraneous chemical manipulations...
In oligosaccharide synthesis, protecting groups, possible participating groups, promoters/catalysts, reaction conditions, and donor leaving groups and acceptors must all be carefully designed in order to generate the correct regio- and stereochemistry for the new glycosidic bond. Programmable one-pot synthesis has been developed to address the above problems. This strategy is based on the sequential...
This chapter describes the assembly of uronic acid containing oligosaccharides and glycoconjugates. Two strategies are available to access these target molecules, namely a pre-glycosylation oxidation approach, in which uronic acid building blocks are used, and a post-glycosylation oxidation strategy, which employs an oxidation step after the assembly of the oligosaccharide chain. Because uronic acid...
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