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: 1)Substituents (mostly OH or OCH 3 ) 2)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)
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Flavonoids Largest class of the phenolic substances* Plant pigments (yellow and red) Glycosides are naturally (mostly O-glyc but some C-gly) Differ in:
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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 ringDiffer in:1)Substituents (mostly OH or OCH3)2)Nature, position & number of sugar moleculeDiffer 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)
FLAVONOIDS BASIC STRUCTURE
C6-C3-C6 SKELETON(2-Phenyl-γ -chromone)
A
B
O
O
C6
C3
1
2
3456
2'
3'
5'87
6'
4'
C6
Steps in the biosynthesis of the flavonoids
1- Formation of the 15 carbon skeleton2- Modification of the central heterocycle
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)
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
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
Naringin & Neohesperidin & Hesperidin• Both are very bitter flavanones• Naringin from grapefruit peel; Citrus paradise (Rutaceae)• Neohesperidin from bitter orange Citrus aurantium peel
• 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.
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
• 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