Flavonoid

The flavonoid compounds are regarded as C6-C3-C6 compounds, (fifteen carbon skeleton) in which each (6 moiety is a benzene ring, the variation in. the state of oxidation of the connecting C3 moiety determines the properties and class of such compounds.

Flavonoid compounds usually occur in plants as glycosides in which one or more of the phenolic hydroxyl groups are combined with sugar residues. The hydroxyl groups are generally found in positions 5 and 7 in ring A, while ring B commonly carries hydroxyl or alkoxyl groups.

These occur in almost all parts of plants. Numerous physiological activities have been attributed to them; few of them act as -cardiac stimulants; while hesperidin, appear to strengthen weak capillary blood vessels; highly hydroxylated flavones act as diuretics and as antioxidants to lipids.

Flavonoids consists of aromatic ring A, condensed to heterocyclic ring C attached to second aromatic ring B. The structure is known as flavonoid diphenyl propane skeleton.

Flavonoids are divided into two sub-classes i.e. anthocyanins and anthoxanthins. Anthocyanins are glycosides of anthocyanidin and are the most important class of water soluble plant pigments responsible for various beautiful colours such as purple, blue and red to fruits, flowers and leaves.

Anthoxanthins are white or yellowish or colourless compounds and includes flavonols, flavanols, isoflavones and flavanones.