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Flavonoids

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 Differ in: Substituents (mostly OH or OCH 3 )

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Flavonoids

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  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 Differ in: Substituents (mostly OH or OCH3) Nature, position & number of sugar molecule Differ in: 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 (flavoneaglycone) 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

  13. Naringin & Neohesperidin Derivatives • Dihydrochalcones derivatives of naringin & hesperidin are intensely sweet (300-1000 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

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