Glycosides

products of the combination (by means of readily hydrolyzable glycoside bonds) of cyclic 5- and 6-membered sugars with alcohol- or phenol-type materials. Glycoside bonds are formed between the acetal hydroxyl group of sugar and the hydroxyl group of the noncarbohy-drate component—the so-called aglycon (with the splitting off of a molecule of water). Depending on the participation of S, O, or N atoms in the formation of glycoside bonds, S-, O-, and N-glycosides are formed. The latter two groups of glycosides are very widespread in vegetable and animal tissues. The α and β-glycosides are differentiated by the spatial arrangement of the aglycon with respect to the plane of the carbohydrate component ring. The hydrolysis of these components takes place with the participation of the enzymes α- and β-glycosidase.

The Classification of glycosides is complicated by the variety of materials that function as the aglycon components and determine the specific biological action of the corresponding glycosides. Glucose-containing glycosides are called glucosides. The glycosides containing disaccharide residues include crocin (containing gentiobiose) and xanthorhamnin (rhamnose). Polysaccharides, which are also formed by glycoside bonds, are frequently included among the glycosides, but the enzymes that split these substances (for example, amylase) are included among the glycosidases. Many glycosides are dyes. A number of glycosides exhibit significant biological activity and are used in medicine and biology. The so-called cardiac glycosides, which are present in plants (the foxglove, lily of the valley, and Strophanthus), cause changes in heart activity; they are used for cardiac ailments, since they are capable of increasing the contraction of the heart muscle, strengthening and shortening the systole, and lengthening the diastole, which improves the heart’s blood circulation and eliminates congestion phenomena. The glycoside phlorizin is used experimentally for inducing glycosuria. The glycoside sapogenin induces erythrocyte hemolysis. An important role in the body is played by the glycosides that are formed upon the combination of ribose and deoxyribose sugars with nitrogen-containing bases—the so-called nucleosides. Their phosphorus derivatives, the nucleotides, participate in the building of nucleic acid and also are coenzymes.