glycoside

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Related to glycosidic: Glycosidic bond

Glycoside

A large important class of sugar derivatives in which the sugar is combined with a nonsugar. In their cyclic forms, monosaccharides (simple sugars) possess one carbon (C) atom (the anomeric carbon) that is bonded to two oxygen (O) atoms; one oxygen atom forms a part of the ring, whereas the other is outside the ring (exocyclic) and is part of a hydroxyl (OH) group. If the oxygen atom of the anomeric hydroxyl group becomes bonded to a carbon atom, other than that of a carbonyl (C ═ O) group, the resulting compound is a glycoside. A glycoside thus consists of two parts (see illustration): the sugar (glycosyl) unit, which provides the anomeric carbon, and the moiety (the aglycon), which is the source of the exocyclic oxygen and carbon atoms of the glycosidic linkage. Such compounds frequently are referred to as O-glycosides to distinguish them from analogs having a sulfur (thio- or S-glycosides), nitrogen (amino- or N-glycosides), or carbon (anomalously called C-glycosides) as the exocyclic atom on the anomeric carbon. See Monosaccharide

The formation of glycosides is the principal manner in which monosaccharides are incorporated into more complex molecules. For example, lactose (illus. b), the most abundant disaccharide in mammalian milk, has a glycosidic bond involving the anomeric carbon of d -galactose and the C-4 hydroxyl of d -glucose. The anomeric carbon atom can exist in either of two stereoisomeric configurations, a fact which is of immense importance to the chemistry and biochemistry of glycosides. For example, the principal structural difference between cellulose and amylose is that cellulose is β-glycosidically linked whereas amylose is α-linked. Humans are able to digest amylose but are unable to utilize cellulose for food. See Cellulose, Lactose

Structural formulas of two glycosidesenlarge picture
Structural formulas of two glycosides

A very large number of glycosides exist in nature, many of which possess important biological functions. In many of these biologically important compounds the carbohydrate portion is essential for cell recognition, the terminal sugar units being able to interact with specific receptor sites on the cell surface.

One class of naturally occurring glycosides is called the cardiac glycosides because they exhibit the ability to strengthen the contraction of heart muscles. These cardiotonic agents are found in both plants and animals and contain complex aglycons, which are responsible for most of the drug action; however, the glycoside may modify the biological activity. The best-known cardiac glycosides come from digitalis and include the drug digoxin.

Glycosidic units frequently are found in antibiotics. For example, the important drug erythromycin A possesses two glycosidically linked sugar units. See Antibiotic

Perhaps the most ubiquitous group of glycosides in nature is the glycoproteins; in many of them carbohydrates are linked to a protein by O-glycosidic bonds. These glycoproteins include many enzymes, hormones, such antiviral compounds as interleukin-2, and the so-called antifreeze glycoproteins found in the sera of fish from very cold marine environments. See Amino acids, Carbohydrate, Enzyme, Glycoprotein, Hormone

Glycolipids are a very large class of natural glycosides having a lipid aglycon. These complex glycosides are present in the cell membranes of microbes, plants, and animals. See Glycolipid, Lipid

glycoside

[′glī·kə‚sīd]
(biochemistry)
A compound that yields on hydrolysis a sugar (glucose, galactose) and an aglycon; many of the glycosides are therapeutically valuable.
References in periodicals archive ?
Glycosidic bond formation is achieved by a chemical reaction between the anomeric carbon atom (C1) of one monosaccharide molecule and a hydroxy group of another monosaccharide molecule, and results in an oxygen bridge between the two molecules.
The cellulose is formed by glycosidic linkages and hydroxyl group with a small amount of carboxyl, whilst hemicellulose and lignin are predominated by ether bonds with hemicellulose characterized by the amount of carboxyl groups.
15) Enzymes involved in glycosidic bond synthesis represent more than 1% of all open-reading-frame genes in M.
Pectinase is a generic name for a family of enzymes that catalyse hydrolysis of the glycosidic bonds in the pectic polymers [5].
Indeed hydrolysis of glycosidic bonds joining monosaccharide units in oligo and polysaccharides can be catalyzed by either acids or enzymes.
Most Senna species that occur in Brazil present piperidine alkaloids as majority constituents, besides glycosidic flavones, long chain aliphatic esters, glycosidic chromone and polyssaccharides (VIEGAS JUNIOR et al.
Polysaccharide may be degraded/fragmented through cleavage of inter-subunit glycosidic bonds by chemical reactions that often involve simple but randomly-acting acid or reactive oxygen species, or biological reactions that often involve complex but specific enzymes [1, 2].
Glycyrrhizin is a triterpenoid glycosidic saponin used as an intense sweetener in candies and for its purported beneficial effects against inflammation, viruses, ulcers, and gastrointestinal discomfort.
Lysozyme splits the [beta] 1, 4, glycosidic linkages between N-acetylmuramic acid and N-acetylglucosamine in the cell walls of Gram-positive bacteria thus preventing them from invading (Paulsen et al.
Tandem mass spectrometric fragmentation of these antibiotics show two types of dissociations: a) cleavage of glycosidic linkages attaching the sugars to the macrolide ring and elimination of water, and b) macrolide ring opening cleavages.
These cyclodextrins have a hydrophilic outside and hydrophobic cavity surrounded by glycosidic units.
crocetin and its glycosidic crocin) that are considered to be pharmacologically active.