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 ?
Alkali degrades ester and glycosidic side chains resulting in structural alterations of lignin, cellulose swelling and partial decrystallization of cellulose.
1]) were attributed to the C-O stretching vibration mode [63], and the third peak is characteristic of the C-O-C groups in glycosidic units or the [beta]-(1-4) glycosidic linkages between glucoses in cellulose (1160 [cm.
Stauffer explained, "TREHA trehalose, used as a food and beverage ingredient, consists of two glucose molecules bound by an [alpha] [alpha]- 1,1 glycosidic linkage.
Hydrolysis was needed to break the glycosidic linkage in order to get the constituent of monosaccharide units.
43) Cellulase is a group of glycoside hydrolase enzymes that hydrolyze the [beta]-(1 [right arrow] 4) glycosidic bonds in cellulose.
Chitin is a biopolymer composed of N-acetyl D-glucosamine units linked by [beta]-1, 4 glycosidic bonds.
2) are exoacting enzymes that cleave non-reducing chain ends of amylase, amylopectin and glycosidic linkages in amylopectin and results in incomplete degradation of the molecule yielding maltose and [beta]- limit dextrins.
s University of Reading used a range of model fecal fermentation systems to determine how monosaccharide composition, glycosidic linkage and molecular weight would affect the selectivity of the fermentation.
Interactions between anthocyanins and non-anthocyanin-polyphenolics in both their glycosidic and their aglycone forms were also investigated to determine additive or nonadditive responses.
Coverage includes the substitution of sugar hydroxyl groups; substituting glycosidic oxygen with carbon, cyclitols and carbasugars where the endocyclic oxygen is replaced with carbon; and other types of endocyclic heteroatom substitutions.