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Flavonoids

Flavonoids are a class of plant secondary metabolites with a polyphenolic structure, primarily found in fruits, vegetables, and flowers, playing roles in plant defense, pigmentation, and growth regulation. They possess antioxidant, anti-inflammatory, anti-ulcer, and anti-atherosclerotic properties, with various subtypes such as flavones, flavonols, and anthocyanidins exhibiting different chemical and physical characteristics. Flavonoids also interact with certain enzymes and are important for human health due to their protective effects against reactive oxygen species and other health conditions.

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FLAVONOIDS
• Class of plant secondary metabolites • Word Flavonoids derived from latin word: “Flavus”= yellow • Group of polyphenolic compounds which are found in fruits, flowers, seeds & vegetable
Structure of flavonoids: The flavonoids are possessing 15 carbon atoms; two benzene rings joined by a linear three carbon chain the skeleton can be represented as the C6 - C3- C6 system.
Physiological role: 1- Role in plant defense mechanism:- They have a very limited role in this respect due to their low toxicity when compared with other plant secondary metabolites such as alkaloids. 2- They are the pigments of flowers and attract pollinating insects. 3- They play a role in plant growth control by inhibiting & activating enzymes.
Physical Properties 1. Crystalline solids, sharp Melting point 2. Solubility: in H2O & alcohol (Flavonoid glycoside). Non glycosidic flavonoid: Aglycone part-sol. in organic solvents 3. Color: Flavonones, Flavanol, Isoflavones- Colorless: Flavonols, Flavones: Yellow, Chalchones, aurones: Yellow Orange 4. Anthocyanidin : Red, blue, Purple 5. optically active
Chemical properties • 15 C skeleton, 2 benzene linked by heterocyclic pyran ring • Being phenolic, dissolves in alkalies →Yellow sol. +HCl → colorless • Glycosidic linkage located at 3 or 7 C • Flavanones, Flavonones are unstable compound , on oxidation → Chalcones, leucocyanidines • Flavonoid + FeCl3→ green/ purple/ red to brown color
CLASSIFICATION • The three-carbon (-C3-) may be included through an oxygen bond between the two phenyl rings into: • A five-membered heterocyclic ring (furan) as in aurones. • A six-membered heterocyclic ring (pyran) to give flavonoids which constitute the largest group. The flavonoid aglycone consists of a benzene ring (A) condensed with a six membered ring (C) pyran ring, which at 2nd position adds a phenyl ring (B) as a substituent. C6-C3-C6 structure
1. Flavones (2-phenylchromen-4-one): Have a double bond between positions 2 and 3 and a ketone in position 4 of the C ring. ex:- Apigenin, Luteolin 2.Flavonols: Have a hydroxyl group in position 3 of the C ring, which may also be glycosylated. Ex: Kaempferol, Rutin, Myricetin, Quercetin. 3. Flavanones: Have C ring saturated; the double bond between positions 2 and 3 is saturated, ex:Hesperetin, Hespereidin, Naringenin 4. Flavanonols : ex:Taxifolin, Silymarin
5. Isoflavones and Neoflavonoids ids can be regarded as abnormal flavonoids. 6. Flavanols Ex: Catechin 7. Anthocyanidins : Anthocyanidins are common plant pigments. Color of the anthocyanins depends on pH. 8. Chalcones and dihydrochalcones
CHEMICAL TESTS
ACTIONS OF FLAVONOIDS 1-Flavonoids as antioxidants: The flavones and catechins seem to be the most powerful flavonoids for protecting the body against reactive oxygen species (ROS). 2- Anti ulcer effect: Majority of peptic ulcers are associated with helicobacter pylori, Quercetin seems to play a very important role in the prevention and treatment of peptic ulcer.
3- Anti atherosclerotic effects: Flavonoids seems to suppress LDL oxidation and inflammatory progression in the artery wall. 4- Anti-inflammatory effect: flavonoids like quercetin are shown to inhibit the cyclooxygenase pathway. This inhibition reduces the release of arachidonic acid.
5-Hepatoprotective activity: Many flavonoids have also been found to possess hepato-protective activity e.g silymarin, apigenin, quercetin and naringenin.