Deoxy and Amino Sugars

Several common sugars lack the complete complement of hydroxyl groups; examples of these are shown in Figure 1-10. Deoxy sugars, in which a hydroxyl group is replaced by a hydrogen, include 2-deoxy-D-ribose, L-fucose (6-deoxy-L-galactose), and L-rhamnose (6-deoxy-L-mannose). L-Fucose is a constituent of many glycoproteins and serves as a signaling epitope for physiological events—for example, in the inflammatory response. The presence of fucose in crucial oligosaccharides of cell surface glycoproteins is required for recruitment of leukocytes to sites of inflammation and injury L-Rhamnose occurs in plant polysaccharides, and 2-deoxy-D-ribose is the sugar constituent of deoxynucleic acids.

In the common amino sugars, the C-2 hydroxyl group is replaced by an amino group. These common amino sugars are D-glucosamine (2-amino-2-deoxy-D-glucose) and

D-galactosamine (2-amino-2-deoxy-D-galac-tose), which usually occur as the /V-acetyl derivatives (yV-acetyl-D-glucosamine and N-acetyl-D-galactosamine). They are constituents of glycosaminoglycans and of many glycoproteins. Glycoproteins may also contain the sialic acids, which are /V-acyl derivatives of neuraminic acid, a unique nine-carbon amino deoxy keto sugar acid. Although the amino group of neuraminic acid is frequently ace-tylated in sialic acids, other acyl groups may be present in sialic acids. /V-Acetylneuraminic acid is also an important biological signaling epitope of glycoproteins. One role it seems to play is protection of circulating plasma proteins from degradation by proteases. Chemically neuraminic acid is very sensitive to acid degradation, and its glycosidic linkage in glycoproteins and gangliosides is very easily hy-drolyzed.

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Responses

  • ami
    Is sialic acid a deoxy sugar derivative?
    6 years ago

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