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  2. FLAVONOIDS •The flavonoids are polyphenolic compounds possessing 15 carbon atoms; two benzene rings joined by a linear three carbon chain having the carbon skeleton C6 - C3 - C6 and they are the plant pigments and they are having polar nature and is solouble in methanol and water. •Flavonoids constitute one of the most characteristic classes of compounds in higher plants. Many flavonoids are easily recognised as flower pigments in most angiosperm families (flowering plants).
  3. • However, their occurence is not restricted to flowers but include all parts of the plant. • They are secondary metabolite and effective in CNS disorders.
  4. Flavonoids Act like antioxidants. How effective they are depends on their molecular structural characteristics Some flavonoids in hops and beer have been found to have better antioxidant effects than tea or red wine; most flavonoids are found in fruits, vegetables, teas, and other drinks. Flavonoids have been known to have antiviral, anti- allergic, antiplatelet, anti-inflammatory, antitumor and antioxidant activities
  5. Flavonoids  Polyphenolic compounds with 15 C atoms, 2 benzene rings on linear 3 C chain Over 4,000 flavonoids Easily recognized as flower pigments in most angiosperm plants but are not always flower pigments  In plants they repair damage and shield from environmental toxins The Most Important Classes of Flavonoids and their Biological Significance Class number of known members biological significance (so far as known) anthocyanin(s) 250 red and blue pigments Chalcones 60 yellow pigments Aurones 20 yellow pigments Flavones 350 cream-coloured pigments of flowers Flavonols 350 feeding repellents (?) in leaves Dihydrochalcons 10 some taste bitter Proanthocyanidins 50 astringent substances Catechins 40 some have properties like those of tannins Isoflavonoids 15 oestrogen effect, toxic for fungi
  6. TESTS FOR FLAVONOIDS 🞭 The extracts were dissolved in ethanol, filtered and subjected to following tests. 🞭 Shinoda test: The dried extracts were dissolved in 95% ethanol (5ml) and few drops of concentrated hydrochloric acid (HCL) were added. Then the magnesium turnings were put into the solution and observed for appearance of pink color. 🞭 Lead acetate solution test: To small quantity of above residue, lead acetate solution was added and observed for appearance of formation of yellow colored precipitates.
  7. CORE STRUCTURES AND NOMENCLATURE • The nomenclature of flavonoids proper is straight-forward with the aromatic ring A condensed to the heterocyclic ring C and the aromatic ring B most often attached at the C2 position. The various substituents are listed first for the A and C ring and - as primed numbers - for the B ring (note that the numbering for the aromatic rings of the open-chained precursor chalcones is reversed). • (Harborne JB, ed. (1988) The Flavonoids. Advances in Research. Chapman & Hall.) O O OH OH O O O O OH O OH + O Flavanone O Dihydroflavonol Flavan-3-ol Flavone Flavon-3-ol Anthocyanidin OH O Chalcone A B O O Isoflavone O Neoflavone A B O C Flavonoids Society For Free Radical Biology and Medicine W . B
  8. FLAVONOIDS & THEIR EXAMPLES 🞭 Flavone:- 🞭 Flavonol:- Luteolin, Apigenin, Tangeritin Quercetin, Kaempferol, Myricetin, Fisetin, Isorhamnetin, Pachypodol, Rhamnazin 🞭 Flavanone:- Hesperetin, Naringenin, Eriodictyol, Homoeriodictyol 🞭 Flavanonol- Taxifolin, Dihydrokaempferol
  9. FLAVONES 🞭 These are yellow pigments which occur in plant kingdom either in the free state or as glycosides associated with tannins.These are also known as anthoxanthins. 🞭 Chemically they are hydroxylated derivative of flavone(2-phenyl-4-chromone) which are partially alkylated. 🞭 In most of the flavones, positions 5 and 7 are hydroxylated and also one or more positions 3,4,5 are also hydroxylated.Further positions 3’and 5’are often methylated whereas positions 5,7 and 4’ are usually unmethylated.
  10. 🞭 When a flavone is hydrolysed with mineral acid, it yields an aglycon and one or more molecules of sugars. The sugars are generally glucose, rhamnose etc. Flavones may exist as C-glycosyl derivatives as well as O-glycosides, eg: vitexin and isovitexin G HO O OH G HO O OH OH O OH O O O C h r o m o n e F l a v o n e 1 O 2 3 4 O 5 6 7 8 1' 2' 3' 4' 5' 6'
  11. PROPERTIES OF FLAVONES 🞭 Most flavones are yellow solids 🞭 Most flavones are soluble in water, ethanol and dilute acids and alkalis. 🞭 Flavones are precipitated by lead salt. 🞭 With ferric chloride, flavones give either a dull green or a red brown colour.
  12. OH O + Cl - O Cl - + H + O + O OH}Cl- Different structures of oxonium salts of flavones. Flavones exhibit two absorption bands: Band I 330-350 nm and Band II,250-270 In acidic medium, flavones are usually more highly coloured than the bases from which they are derived. In acidic medium flavones form oxonium salts which impart this colour. However these oxonium salts are very unstable in presence of water. The flavones differ in this respect from the anthocyanidins which give strong oxonium salts and are found as such in plants.
  13. Diluted with water,acidified with HCl and boiled for some ho Exctracted with alcohol & carried out fractional crystallis Digestion with boiling water Water extract diluted and treated with lead acetate Filteration Precipitate of tannins Flavonoids in supernatant liquid Ground plant material Acetate free flavonoids Precipitate of sugar free flavonoids
  14. SEPARATION & PURIFICATION OF FLAVONES PAPER CHROMATOGRAPHY 🞭 Convenient means of separating and purifying flavones on milligram scale Dried plant material is extracted with either 70 % or 80 % methanol. The aqueous extract is then concentrated to a small volume in vacuo and refiltered if necessary. An aliquot of this concentrate should be applied on Whatman No. 3 filter paper.
  15. Separation of the flavones present in concentrate is generally carried out in the solvent mixture BAW(n-butanol-acetic acid- water),4:1:5 Individual bands are eluted and concentrated . Further fractioned in water, 5 % acetic acid. Purified in n-butanol-ethanol-water(4:1:2.2)
  16. GENERAL METHODS FOR THE ELUCIDATION OF STRUCTURE OF FLAVONOLS 🞭 Flavonol shows characteristic bands at 350-390 nm and 150-270 nm in ultraviolet spectrum. 🞭 The molecular formula of flavonol has been found to be C15H10O3 🞭 It can be acetylated to give an ester shows the presence of a hydroxyl group. 🞭 C15H9O2(OH)+ CH3COCl C15H9O2(OCOCH3)+HCl 🞭 When methylated followed by fusion with KOH, flavonol yields phenol and benzoic acid. Both these products do not possess methoxyl group. This shows that the methoxy group must be present at C3 which must have been lost in KOH fusion. C 1 5 H 1 0 O 3 M e t h y l a t i o n a n d f u s i o n w i t h K O H O H + C O O H f l a v o n o l p h e n o l b e n z o i c a c i d
  17. 🞭 When flavanol is boiled with an ethanolic solution of potassium hydroxide, it yields a mixture of o- hydroxybenzoylmethanol and benzoic acid. The formation of these products reveals that flavonol contains a hydroxy group at C3. Hence flavanol must be 3-hydroxyflavone(3-hydroxy- 2-phenyl-ϒ-chromone) 🞭 On the basis of the above structure of flavanol,the foregoing reactions can be explained as follows: O C 6 H 6 O H O Fl a va n o l
  18. O O C6H6 OH Flavanol + CH3COCl O O C H 6 6 + HCl OCOCH 3 Acetyl derivative of flavonol O O C6H6 OH methylation (CH3)2SO4/NaOH O O C6H6 OCH 3 KOH Fusion HOOC + OH Phenol Benzoic acid O O C6H6 OH KOH Boiling OH O OH C6H5 OH OH O COC 6H5 OH OH + C6H5COOH COCH 2OH o-hydroxybenzoyl methanol Benzoic acid a) b) c)
  19. Synthesis The above structure of flavanol has been confirmed by its various syntheses a)Robinson’s synthesis. In this synthesis ω-methoxy-2-hydroxyacetophenone is condensed with benzoic anhydride in the presence of its potassium salt OH COCH 2OMe + (C6H5CO)2O O OMe C6H5 O HI O C6H5 OH O Flavanol
  21. USES 🞭 Preliminary research 🞭 Antiviral 🞭 Hyperoside (which is the 3-O-galactoside of quercetin) is a strong inhibitor of HBsAg and HBeAg secretion 🞭 Quercitrin and myricetin 3-O-beta-D-galactopyranoside inhibit HIV-1 reverse transcriptase, all with IC50 values of 60 μM. 🞭 Quercetin can also inhibit reverse transcriptase, part of the replication process of retroviruses. The therapeutic relevance of this inhibition has not been established.
  22. 🞭 Asthma 🞭 Quercetin is an effective bronchodilator and helps reduce the release of histamine and other allergic or inflammatory chemicals in the body. 🞭 Quercetin has demonstrated significant anti-inflammatory activity because of direct inhibition of several initial processes of inflammation. 🞭 Eczema 🞭 Serum IgE levels are highly elevated in eczema patients, and virtually all eczema patients are positive for allergy testing. Excessive histamine release can be minimized by the use of antioxidants. Quercetin has been shown to be effective in reducing IgE levels in rodent models.
  23. 🞭 Inflammation 🞭 Several laboratory studies show quercetin may have anti- inflammatory properties, and it is being investigated for a wide range of potential health benefits. 🞭 Quercetin has been reported to be of use in alleviating symptoms of pollinosis. An enzymatically modified derivative was found to alleviate ocular but not nasal symptoms of pollinosis. 🞭 Studies done in test tubes have shown quercetin may prevent immune cells from releasing histamines which might influence symptoms of allergies. 🞭 A study with rats showed that quercetin effectively reduced immediate-release niacin (vitamin B3) flush, in part by means of reducing prostaglandin D2 production. A pilot clinical study of four humans gave preliminary data supporting this. 🞭 Quercetin may have properties of a calcineurin inhibitor, similar to cyclosporinAand tacrolimus, according to one laboratory study.
  24. 🞭 Fibromyalgia 🞭 Quercetin may be effective in the treatment of fibromyalgia because of its potential anti-inflammatory or mast cell inhibitory properties shown in laboratory studies 🞭 Cancer 🞭 Laboratory studies have investigated Quercetin's potential for use in anti-cancer applications. The American Cancer Society says quercetin has been promoted as being effective against a wide variety of diseases, including cancer.
  25. 🞭 Metabolic syndrome 🞭 Quercetin has been shown to increase energy expenditure in rats, but only for short periods (fewer than 8 weeks). Effects of quercetin on exercise tolerance in mice have been associated with increased mitochondrial biogenesis.In mice, an oral quercetin dose of 12.5 to 25 mg/kg increased gene expression of mitochondrial biomarkers and improved exercise endurance. 🞭 It has also been claimed that quercetin reduces blood pressure in hypertensive and obese subjects in whom LDL cholesterol levels were also reduced. 🞭 In vitro studies showed quercetin and resveratrol combined inhibited production of fat cells and vascular smooth muscle cell proliferation. 🞭 Supplements of quercetin with vitamin C and niacin does not cause any significant difference in body mass or composition and has no significant effect on inflammatory markers, diagnostic blood chemistries, blood pressure, and blood lipid profiles.
  26. 🞭 Monoamine-oxidase inhibitor 🞭 Possibly an active component of heather (Calluna vulgaris), quercetin was suspected from a bioassay test on crude extracts to selectively inhibit monoamine oxidase, possibly indicating pharmacological properties. 🞭 Prostatitis 🞭 Quercetin has been found to provides significant symptomatic improvement in most men with chronic prostatitis, a condition also known as male chronic pelvic pain syndrome.
  27. REFERENCES 🞭 1)Organic chemistry of natural products; vol 1 ; O.P. Agarwal ; pg no :350-406 🞭 2)Organic chemistry of natural products ; vol 2; Gurdeep. R. Chatwal ; pg no : 2.1 – 2.40 🞭 3)Organic chemistry ; vol 2 ; stereochemistry & chemistry of natural products ; I. L .Finar ; 5th edition ; pg no : 425