Flavonoid Glycosides PDF

Flavonoid glycosides Flavonoid is the largest class of naturally occuring plants products, they are polyphenolic compounds. They occur both in the free state and as glycosides; most are O-glycosides but a considerable number of flavonoid C- glycosides are known. According to their n...

Flavonoid glycosides Flavonoid is the largest class of naturally occuring plants products, they are polyphenolic compounds. They occur both in the free state and as glycosides; most are O-glycosides but a considerable number of flavonoid C- glycosides are known. According to their name, they are usually yellow-coloured compounds (flavus is a latin word yellow colour). Flavonoids are found in fruits, vegetables, grains, bark, roots, stems, flowers, tea and wine. These natural products were known for their beneficial effects on health long before flavonoids were isolated as the effective compounds. All derived from the same parent nucleus, 2-phenyl-benzopyran (flavan), thus they have a basic C6-C3-C6 skeleton. Pyran Benzopyran benzopyrone According to the oxidation level of central pyran ring, they can be classified into: flavones flavonols isoflavones flavanones anthocyanidins.  Physico-chemical Properties, Extraction, Characterization, And Quantitation Although, as general rule, glycosides are water-soluble and soluble in alcohols. Aglycones are, for the most part, soluble in a polar organic solvents; when they have at least one free phenolic group, they dissolve in alkaline solutions. Lipophilic flavonoids are directly extracted by solvents of medium polarity (ex., dichloromethane); next they must be separated from the waxes and fats extracted simultaneously (ex. a preliminary hexane wash is possible). The glycosides can be extracted, most often at high temperature, by acetone or by alcohols (ethanol, methanol) mixed with water.  Solvent evaporation under vacuum can be the next followed, when only the aqueous phase is left, by a series of liquid-liquid extractions by non-miscible solvents. Ethyl acetate which dissolves the majority of glycosides. The free saccharides remain in the aqueous phase with the most polar glycosides when these are present. The separation and purification of the different flavonoids is based on the usual chromatographic techniques ( HPLC) In certain specific instances either the 6- membered heterocyclic ring (pyrones) is replaced by a 5 membered heterocyclic ring (aurones) or exists in an open-chain isomeric form (chalcones). Chalcones, have no central pyrone ring, so they are not true flavonoidal compounds. Aurones are oxidized forms that are obtained by enzymatic oxidation. They have five membered pyrone ring. Chalcon Aurone Properties of flavonoids Flavonoids dissolve in alkali give intense yellow colour solution, on the addition of acid become colourless. Flavonoids exhibit strong fluorescence under UV light. Flavonoidal glycosides are soluble in water and alcohol. Ethylacetate is the solvent of choice for the extraction of flavonoids from aqueous solution. Flavonoids compounds may be characterized through the investigation of their UV Spectra.  Biological Properties The main property that is recognized for flavonoids is «venoactivity», in other words their ability to decrease capillary permeability and fragility. Because of this property they were referred as «vitamin P». Vitamin P is more active together with vitamin C. Flavonoids and Free Radicals Many properties, shown in vitro, could explain the actions of flavonoids. Initially, it was postulated that they act on the reduction of dehydroascorbic acid via glutathione by acting as hydrogen donors.  It is now more generally accepted that the phenols and flavonoids scavenge free radicals formed under different circumstances : anoxia inflammation lipidic autoxidation Biochemically, free radicals are thought to be responsible for nucleic acid alterations, mutations, initiations and promotion of carcinogenesis, and cellular damage, because of their ability to react with membrane phospholipids, among other reason. The antagonist effect towards free radical production can be studied experimentally. This has spurred research, including epidemiologic studies, on the potential role of antioxidants (i.e., free radical scavengers), such as flavonoids, in preventative therapy. Examples of flavonoid glycosides: 1- Flavone glycoside Diosmin: flavone glycoside Occurance: Barosma crenulata F. Rutaceae. It has diuretic, diaphoretic action and anti- Helicobacter pylori activity Upon hydrolysis, diosmin yields rhamnose, glucose and diosmetin. 2- Flavonol glycoside: Rutin and quercetrin: are examples of flavonol glycosides a- Rutin :It is the 3-rhamnoglucoside (called rutinose) of the genin quercetin. It gives on hydrolysis the aglycone (quercetin) beside one molecule of glucose, and one molecule of rhamnose. Rutin is used to Decrease capillary fragility. b- Quercetrin is quercetin 3-O-rhamnoside. Quercetrin yield upon acid hydrolysis rhamnose and quercetin. The aglycone quercetin has a diuretic action. 3-Flavanones: Hesperidin: it is an example of flavanones. It is the main flavonoidal glycoside of citrus fruits. Upon hydrolysis by acid, hesperidin gives rhamnose, glucose and hesperitin. Uses:- Hesperidin is necessary for absorption and retention of vit C that lead to decrease capillary fragility. 4- Silymarin The leaves and fruits of Silybum marianum family Compositae contain silymarin (silybin). Uses: 1- Silymarin is a very effective lipotropic and hepato protective therapy. 2- It is a free radical scavenger. 3- Supportive treatment of acute and chronic alcoholic poisoning and toxin induce hepatitis. 4- It is used for treatment of liver cirrhosis caused by plant toxins (mushroom), silymarin is applied as intravenous injection.