Protecting Group Manipulations in Carbohydrate Synthesis

Oligo- and polysaccharides are the most structurally diverse biomolecules due to the polyfunctional nature of the monomeric building blocks and the many different linking modes of these monomers. This great diversity makes carbohydrates suitable to play crucial roles in biological recognition and regulation processes. At the same time, the structural complexity has the consequence that unlike proteins and nucleic acids there is no general method for the synthesis of glycans, neither are there universal building blocks. Access to unique and homogeneous carbohydrates to reveal the relationship between their structure and function requires unique and sophisticated synthetic methods, one of the pillars of which is the regioselective protection of the saccharide building units. This chapter aims at briefly discussing the carbohydrate-specific aspects of selection and regioselective introduction of protecting groups, as well as the significance of orthogonality between blocking groups in the synthesis of oligosaccharides. The methods available for the introduction and the removal of different types of hydroxyl and amino protecting groups commonly used in carbohydrate chemistry are discussed in detail. Over the past 10–15 years, we have witnessed enormous progress in the field of protecting group chemistry of carbohydrates. The orthogonal sets of protecting groups have expanded, ether-type stereodirecting groups have appeared, exciting catalytic site-selective protection methods have emerged, and fascinating one-pot and semi-one-pot protection strategies have been developed. In this chapter, which is based on the chapter of the same title of the previous edition of Comprehensive Glycoscience, we intend to follow this progress.