1. Flavonoids Largest class of the phenolic substances*
Plant pigments (yellow and red)
Glycosides are naturally (mostly O-glyc but some C-gly)
Differ in:
Oxidation stage of the heterocyclic ring
Substituents (mostly OH or OCH3)
Nature, position & number of sugar molecule
Occurrence within the plant cell: cytoplasm/cell sap
*(Flavan3-ols [catechins] and flavan 3, 4-diols will be discussed in the chapter of the tannins)

2. FLAVONOIDS BASIC STRUCTURE
C6-C3-C6 SKELETON
(2-Phenyl-γ -chromone)

3. Steps in the biosynthesis of the flavonoids
1- Formation of the 15 carbon skeleton 2- Modification of the central heterocycle [oxidation level] (chalcone, aurone, flavonone, flavononol, flavone, flavonol, anthocyanidine) 3- Timing of the substitution in ring B (hydroxylation, methylation) 4-Formation of glycosides (O-glycosides, C-glycosides)

4. Flavonoids Biosynthesis
Biosynthesized from shikimate (cinnamic acid part) forming starting molc. & acylpolymalonate (3 acetate residues) pathways. Followed by ring closure.

5. Classes of flavonoids Chalcones Aurones Flavonones
Flavononols (Dihydroflavonols)
Flavones
Flavonols
Isoflavones
Biflavonoyls
Flavan-3-ols, flavan-3,4-diols
Anthocyanines
Flavonolignans

6. Classification Of Flavonoids
Based on degree of oxidation & saturation of ring B
I)Phenylchromones:
II) Phenylchromanes:
Flavan 3,4-ol

7. Classification of Flavonoids
III) Chalcones: IV) 2-Benzylidene coumaranones: V) Phenylbenzylpyrilliums: (flavylium ion) VI) Isoflavonoids:

8. Anthocyanidines are intensely colored substances (scarlet, blue, purple, red). The anthocyanidins in Hydrangea, colors it RED in acid soil and BLUE in alkali soil. Anthocyanidines are the aglycones while anthocyanines are glycosides of them (anthocyanidine + sugar→anthocyanine)

9. Role of Flavonoids Abundant in plant kingdom
Important chemotaxonomic interest
Minimal medicinal application
Antioxidants
Rutin (flavone aglycone) is known as Vit P = permeability vit?? (inc. strength of fragile capillaries wall)
Derivatives of some flavonoids used in pharmaceutical & dietary industries

10. Ecological importance of the flavonoids
Pollinating agents
Germination and growth regulation (involved in IAA/IAA oxidase system of the plants)
Involvement in the biochemistry of sex determination of the plants
Protection of the plants against attack of parasites (i.e. fungicidal activity)

11. Rutin
Extracted from:
Buds of Sophora japonica (Fabaceae) Indonesian tree
Fagopyrum esculentum (Polygonaceae) seeds
Eucalyptus macrorhyncha leaves (Myrtaceae)
Rutinose= Rhamnosyl-(α1→6)- Glucose

12. Naringin & Neohesperidin & Hesperidin
Both are very bitter flavanones
Naringin from grapefruit peel; Citrus paradise (Rutaceae)
Neohesperidin from   bitter orange Citrus aurantium peel (Rutaceae)
Hesperidose = Rhamnose- (α-1→2)-glucose
Dihydrochalcones of these compounds produced by hydrogenation in alkaline solution produces a remarkable change to their taste and the products are intensely sweet being some times as sweet as sucrose. Neohesperidin-dihydrochalcone is used as a non sugar sweetening agents.

13. Naringin & Neohesperidin Derivatives
Dihydrochalcones derivatives of naringin & hesperidin are intensely sweet ( X times as sweet as sucrose).
Neohesperidin-dihydrochalcone is used as a non sugar sweetening agent.

14. Isoflavonoids
These compounds are transferred into the body of the mammalians into estrogen-like compounds affecting the reproduction and usually termed phyto-estrogens.
Genistein and daidzein were able to prevent the growth of estrogen-receptor positive and negative breast cancer cells in vitro; recently reported; it is progesterone-dependent
Fabaceae richest source

15. Some important isoflavones and rotenones
Genistein(5-OH, 7-OH, 4'-OH)
Daidzein(7-OH, 4'-OH)
Formonentin (7-OH, 4’-OCH3)

16. Rotenoids
Rotenoids take their name from the first known example rotenone
Common in the Derris and Loncocarpus spp. (Leguminosae)
Piscicidal agents “Lazy fishing”
Classified as natural insecticides
Paralyzing action on insects, with no recoveries
Odorless, stable compounds; biodegradeable
Not recommended for parasite control in human (lice)
Useful in controlling parasites on animals
Used in form of powders or as sprays