glycosylations

Glycosylations are chemical reactions that form glycosidic bonds, linking a glycosyl donor to a glycosyl acceptor to produce glycosides. The term encompasses laboratory methods for assembling defined carbohydrates and the biological processes by which sugars are attached to proteins or lipids. In synthesis, glycosylations enable the construction of oligosaccharides and glycoproteins; in biology, they underlie the formation of glycosylated biomolecules that influence folding, stability, and cellular recognition.

In chemical glycosylation, a glycosyl donor is activated in the presence of an acceptor such as an alcohol. Donors include glycosyl halides, thioglycosides, trichloroacetimidates, and glycosyl fluorides. Activation is typically achieved with Lewis acids or promoters such as TMSOTf, BF3·Et2O, or NIS/TfOH, sometimes in combination with other activators. A major challenge is controlling stereochemistry at the anomeric center; neighboring group participation from a suitably protected C-2 substituent often directs formation of beta or alpha glycosides. Protecting groups on the remaining hydroxyls are chosen to guide selectivity and to enable iterative synthesis of longer glycans. Reaction conditions, solvent, and catalyst choice all influence yield and anomeric outcome. Advances include automated and convergent strategies, and chemoenzymatic approaches that combine chemical steps with enzymatic specificity.

Biological glycosylation refers to the Attachment of sugars to proteins or lipids in living organisms. In eukaryotes, N-linked glycosylation attaches glycans to asparagine within a consensus sequence, and O-linked glycosylation attaches to serine or threonine. These processes occur mainly in the endoplasmic reticulum and Golgi apparatus and are mediated by glycosyltransferases and related enzymes. Glycosylation modulates folding, stability, trafficking, and cell signaling, and aberrant patterns are associated with congenital disorders, cancer, and other diseases.