O- or N-glycosides

Glycoproteins are glycosides that have a protein aglycone. The protein is usually linked to a polysacharide (See section 1.4.4) by an O or N glycosidic link. Glycoproteins are found in all forms of life. They exhibit a wide range of biological activities. For example, they may act as receptors, hormones and enzymes. 

These membranes contain glycoproteins—proteins with amino-sugar residues attached to asparagine, serine, or threonine in the protein. The attachment is at the anomeric position so that these compounds are O- or N-glycosides of the amino sugars. 

Of the many methods described for glycoside synthesis, those predominantly used in current oligosaccharide synthesis, in which the glycosyl donor has O- or N- functionality at C-2 (that is, excluding 2-deoxyglycosides), are the following ... 

On the cell surface of certain glycoproteins, O-glycosidic links are found between the carbohydrate part and a serine or threonine residue, instead of N-glycosidic links to asparagine residues. This type of link is less common than the N-glycosidic one. 

A glycoprotein may contain only one type of glycosidic linkage (N- or O-linked), or may have both O- and N-linked oligosaccharides within the same molecule. Figure 14.13... 

All glycosaminoglycans and keratan sulfate, except hyaluronic add, are covalently linked to protein. Such linkages, shown in Figure 9.13, may be of the O- or the N-glycoside type. Also, at the link region, all glycosaminoglycans contain the -Gal-Gal-Xyl-sequence, in which the xylose molecule, a pentose, is... 

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