Recent Chemical and Chemoenzymatic Strategies to Complex-Type N-Glycans

Abstract

Glycosylation is one of the major forms of protein post-translational modification. N-glycans attached to proteins by covalent bonds play an indispensable role in intercellular interaction and immune function. In human bodies, most of the cell surface glycoproteins and secreted glycopeptides are modified with complex-type N-glycans. Thus, for analytical or medicinal purposes, efficient and universal methods to provide homogeneous complex-type N-glycans have been an urgent need. Despite the extremely complicated structures, tremendous progress in the synthesis of N-glycans has been achieved. On one hand, chemical strategies are shown to be effective to prepare core oligosaccharides of N-glycans by focusing on stereoselective glycosylations such as β-mannosylation and α-sialylation, as well as the methodology of the N-glycan assembly. On the other hand, chemoenzymatic strategies have also become increasingly powerful in recent years. This review attempts to highlight the very recent advancements in chemical and chemoenzymatic strategies for eukaryotic complex-type N-glycans.

Zinc Tetrafluoroborate Catalyzed Stereo‐ and Regioselective O‐Glycosylation for the Direct Synthesis of β‐Glycosides from Armed O‐Glycosyl Trichloroacetimidates

“…Carbohydrates are unique natural metabolites that play a decisive role in energy storage, supply, and metabolism [1] . In nature, the vast majority of carbohydrates prevail as O ‐glycosides in the form of glycoconjugates or polysaccharides, [2] in which sugar units are stereoselectively stitched to another sugar unit or aglycon. Thus glycosylation reactions, [3] which insert carbohydrate moieties onto target molecules (sugar or aglycon), are in great demand across a range of fields to investigate and alter sugar‐mediated biological processes.…”

ZnI2-Mediated β-Galactosylation of C2-Ether-Type Donor

“…1 The great majority of carbohydrates exist as O-glycosides such as glycoconjugates or polysaccharides, in which sugar units are linked to another sugar unit or aglycones. 2 Therefore, the stereoselective construction of Oglycosidic bonds is pivotal for the synthesis of glycosides. The stereochemical outcome of a chemical glycosylation reaction is influenced by multiple chemical and environmental factors, including the structure of the glycosyl donor, the type and position of protecting groups installed on the donor, the nucleophilicity of the acceptor, the solvent in which the reaction is performed, the concentration of substrates, and the reaction temperature, and determined by the specific combination of these factors.…”