Cell-Surface Carbohydrates and Carbohydrate Vaccines

Among the numerous complex polysaccharides that have been synthesized in the laboratory is the Lewis Y hexasaccharide, a tumor marker that is currently being explored as a potential cancer vaccine. 

It has been known for more than a century that human blood can be classified into four blood-group types (A, B, AB, and O) and that blood from a donor of one type can t be transfused into a recipient with another type unless the two types are compatible (Table 21.1). Should an incompatible mix be made, the red blood cells clump together, or agglutinate. 

The agglutination of incompatible red blood cells, which indicates that the body s immune system has recognized the presence of foreign cells in the body and has formed antibodies against them, results from the presence of 

Monosaccharides normally exist as cyclic hemiacetals rather than as open-chain aldehydes or ketones. The hemiacetal linkage results from 

Much of the chemistry of monosaccharides is the familiar chemistry of alcohols and aldehydes/ketones. Thus, the hydroxyl groups of carbohydrates form esters and ethers. The carbonyl group of a monosaccharide can he reduced with NaBH4 to form an alditol, oxidized with aqueous Br2 to form an aldonic acid, oxidized with HNO3 to form an aldaric acid, oxidized enzymatically to form a uronic acid, or treated with an alcohol in the presence of acid to form a glycoside. 

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D. Cell surface carbohydrates and carbohydrate vaccines (Section 25.11). 

Vaccination can prevent the spread of flu, but influenza vaccines are slow to produce and difficult to generalize because of the rate of mutation of the virus. So the first line of defence is a class of antiviral compounds known as neuraminidase inhibitors. Neuraminidase is an enzyme used by the flu virus that targets human cell-surface carbohydrates containing neuraminic acids and allows the virus to release itself from the host cell. Inhibition of this enzyme prevents the new virus particles from spreading. 

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