Glycosides

• The most frequently occurring sugar in glycosides is Beta-D-glucose
• Other sugars that can be components of glycosides include rhamnose, digitoxose, and cymarose
• Glycosides are compounds that yield one or more sugars among the products of hydrolysis
• Acetals in glycosides involve the condensation of the hydroxyl group of the non-sugar component and the secondary hydroxyl within the sugar molecule to form an oxide ring
• Simple glycosides may be considered sugar ethers
• Aglycone or genin is the nonsugar component of glycosides
• Glycone is the sugar component of glycosides
• Both alpha and beta glycosides are possible, depending on the stereoconfiguration of the glycosidic linkage
• Glycosides are involved in plants' regulatory, protective, and sanitary functions
• Some glycosides contain more than one saccharide group, possibly di- or trisaccharides
• All natural glycosides are hydrolyzed into a sugar and another organic compound by boiling with mineral acids
• The ease of hydrolysis of glycosides varies widely
• Most glycosides are easily hydrolyzed by enzymes that occur in the same plant tissue but in different cells from those that contain the glycoside
• Enzymes like Emulsin of almond kernels and Myrosin of black mustard seed hydrolyze a considerable number of glycosides
• Glycosides that are derivatives of Rhamnose require a special enzyme known as Rhamnase for their hydrolysis
• Biosynthesis of glycosides involves the transfer of a uridyl group from uridine triphosphate to a sugar 1-phosphate
• The enzyme catalyzing this reaction are referred to as uridylyl transferases
• The formation of glycosides involves the transfer of the sugar from uridine diphosphate to a suitable acceptor (aglycone)
• Classification of glycoside-containing drugs includes cardioactive steroid group, anthraquinone group, saponin group, cyanophore group, glucosinolate or isothiocyanate group, flavonol group, alcohol group, aldehyde group, and phenol group
• Cardioactive or cardiac glycosides are steroids characterized by their specific and powerful action on the cardiac muscle
• Steroidal glycosides have sugar attached at the 3-position of the steroid nucleus
• Cardiac glycosides are named as such because of their action on the heart muscle
• There are two types of steroidal aglycones or genin: Cardenolides and Bufadienolides
• Foxglove (Digitalis) is derived from Digitalis purpurea and is used in the treatment of congestive heart failure
• Digitoxin is a cardiotonic glycoside from Digitalis purpurea
• Digitoxin yields digitoxigenin (aglycone) and digitoxose (sugar component) upon hydrolysis
• Grecian Foxglove (Digitalis lanata) contains digoxin and aglycones like digitoxigenin, gitoxigenin, and gitaloxigenin
• Convallaria (Lily-of-the-Valley) contains Convallatoxin composed of K-strophanthidin (genin) and G-strophantin (rhamnose), convallatoxol, and convalloside
• Apocynum (Black Indian hemp, Dog bane, or Canadian hemp) contains cymarin as the chief constituent, appocannoside, and cyanocannoside
• Adonis (Pheasant's eye) contains adonitoxin, cymarin, and K-strophantin
• Cactus Grandiflorus (Night-blooming cereus) contains Selenicereus grandiflorus and black hellebore (Christmas rose) contains hellebrin as the chief constituent
• Strophanthus contains k-strophanthoside (stroposide), strophanthidin (genin), and cymarose, B glucose, and alpha glucose
• Squill bulb contains scillaren A as the principal component, which yields scillarenin (aglycone), a bufadienolide, and rhamnose and glucose (glycone) upon hydrolysis
• Anthraquinone glycosides are cathartics and exert their action by increasing the tone of smooth muscle in the wall of the large intestine
• Upon hydrolysis, anthraquinone glycosides yield aglycones that are di-, tri-, or tetrahydroxyanthraquinones or modifications of these compounds
• Glycosides of anthranols and anthrones, reduced derivatives of anthraquinones, also contribute to the therapeutic action of these compounds
• The biosynthesis of anthraquinone glycosides involves the condensation of acetate units to form various oxygenated aromatic compounds
• The distribution of radioactivity in anthraquinone derivatives is consistent with the formation via a head-to-tail condensation of acetate units
• Poly-beta-ketomethylene acid intermediate is likely first produced and then gives rise to the various oxygenated aromatic compounds in anthraquinone glycosides
• Beta-ketomethylene acid intermediate is first produced and then gives rise to various oxygenated aromatic compounds following intramolecular condensations