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Flavonoids Presented by Jisha Shamsudeen M pharm Part-1


CONTENTS Introduction General properties Classification of Flavonoids Isolation of flavonoids Seperation techniques Structural elucidation-spectrometry Structural elucidation –flavone, flavonol Conclusion Reference


Flavonoids Flavonoids are antho xanthidins that are widely distributed as yellow plant pigments Free state or glycosides associated with tannins Found in coloured fruits, vegetables and certain beverages


Flavonoids Some flavonoids are called bioflavonoids. They can also be called vitamin P. Bioflavonoids strengthen the capillary walls and increase the body’s ability to make use of vitamin C. Flavonoids are antioxidants. Antioxidants naturally occur to protect the body from harmful free radicals. Free radicals are thought to promote aging and disease. Flavonoids are often the major component of an herb’s ability to heal.


Flavonoids Flavonoids are chemically polyphenolic compounds 15 carbon atoms two benzene rings joined by a linear three carbon chain. The chemical structure of flavonoids are based on a C15 skeleton with a chromane ring bearing a second aromatic ring B in position 2,3, or 4..

General Properties of flavonoids:

General Properties of flavonoids Crystalline compound Soluble in water, dil mineral acid, alkali,ethanol.alcohol etc Dull green colour with ferric chloride Highly coloured in acidic medium Colour due to oxonium salts

Classification of Flavonoids:

Classification of Flavonoids Flavonoids are classified into Flavones Flavonols Isoflavones Chalcones Aurones Anthocyanins Leucoanthocyanidins Biflavonoids Proanthocyanidins


Flavones Flavone consist of benzo-gamma pyrone ring with phenyl substitution at position 2 of pyrone ring 2,3 dihydroxy derivative of flavone is called flavonone


Isoflavone Isoflavone contains benzo-gamma-pyrone ring with phenyl substitution at position 3 of the pyrone ring


Flavonols Flavonol is 3 hydroxy derivative of flavone


Chalcones Do not contain gamma pyrone ring hence called open chain flavonoids Two aromatic rings are joined by three carbon alpha beta unsaturated carbonyl system


Anthocyanins Occur as flavylium salt structures They are glycosides of anthocyanidins




Biflavone They are dimers of flavonoids


Procyanidin Trimers of flavonoids

Isolation of flavonoids:

Isolation of flavonoids Plant material containing flavonoid is seived to fine powder They extracted by boiling water and the tannins are removed by means of lead acetate

Isolation of flavonoids:

Isolation of flavonoids The filtrate is diluted with water, acidified with HCl, and boiled for some hours

Isolation of flavonoids:

Isolation of flavonoids Flavones gets precipitated, they are extracted with alcohol and may be purified by fractional distillation of their acetates or by recrystallisation from some organic solvents like benzene, carbon di sulphide and alcohol.

Seperation techniques:

Seperation techniques Thin layer chromatography (TLC) High Performance Liquid Chromatography Paper Chromatography Column Chromatography

Thin layer Chromatography:

Thin layer Chromatography Thin-layer chromatography (TLC) is a chromatographic technique that is useful for separating organic compounds Thin-layer chromatography consists of a stationary phase immobilized on a glass or plastic plate, and an organic solvent

Thin layer Chromatography:

Thin layer Chromatography Stationary phase: Silica gel,polyamide Solvent : benzene, pyridine, ammonia(80:20:1)-flavone aglycones Benzene,aceticacid (45:4)- flavanone glycosides Chloroform-methanol,water( 65:45:12)-flavone-o-glycosides

Thin layer Chromatography:

Thin layer Chromatography Spraying agent- beta-aminodiethyl ester of diphenyl boric acid Solvent for seperation flavone aglycones adsorbed on cellulose plate: chloroform, acetic acid, water (10:9:1)

High Performance Liquid Chromatography:

High Performance Liquid Chromatography One of the best method for seperation of flavonoid Used for isolation of pure flavonoid in preperative scale Stationary phase: lichrosorb RP-8 Lichrosorb rp-18, zorbax Mobile phase: methanol.aceticacid,water

Gas Liquid Chromatography:

Gas Liquid Chromatography Analysis of various flavonoids are carried out as silyl ethers Columns used: SE 30, CARBOWAX, APIZON Detectors: TCD, FID Not applicable for hydroxylated flavonoid glycosides

Paper chromatography:

Paper chromatography Flavonoid that are coloured are seperated using Whatmann Filter paper 1 Solvent: n-butanol,acetic acid, water

Column Chromatography:

Column Chromatography Stationary phase: Silicagel, sephadex, polyamide, cellulose Mobile phase: Non polar,polar organic solvents used single or in combination

Spectrometric elucidation:

Spectrometric elucidation UV Spectrometry UV visible spectra of plant pigments is obtained due to different chromophores Chromophores are responsible for the colour produced Confirmation of the position of hydroxyl group – shifting reagents- sodium methoxide & Aluminium Chloride

UV Spectrometry:

UV Spectrometry There are two main absorption bands Band 2- 300-400 nm ( benzoyl ring) Band 1-240-285 nm ( cinnamoyl ring)

Mechanism of bathochromic shift in Flavonoids:

Mechanism of bathochromic shift in Flavonoids

Carbon NMR spectrometry:

Carbon NMR spectrometry Structural elucidation of flavonoid Helps to know the no of carbon atoms Reveals dimer and trimer nature of biflavones, anthocyanidins

Mass spectrometry:

Mass spectrometry Structural elucidation of lavonoids Mass fragentaion pattern establish different types of flavonoid

Determination of structure of flavone:

Determination of structure of flavone Flavones does not contain any hydroxyl group On fusion with alkali,flavones are degraded to a phenol and aromatic acid



Determination of structure of flavone:

Determination of structure of flavone Structure proposed by degradation is finally proved by various synthesis some general methods of synthesis are Kostanecki method Robinson method Baker-Venkataraman method Chalcone method Wheeler method

Kostanecki method:

Kostanecki method

Kostanecki method:

Kostanecki method It is a method of condensing the ester of alkylated salicylic acid with acetophenone or alkylated o-hydroxyacetophenone with the ester of an aromatic acid in the presence of sodium to form an intermediate which on reduction form flavone.

Robinson method:

Robinson method

Robinson method:

Robinson method It is a general method which involves heating o-hydroxyacetophenone with the anhydride and sodium salt of benzoic acid to form flavone

Baker-Venkataraman method:

Baker-Venkataraman method

Baker-Venkataraman method:

Baker-Venkataraman method In this method o-hydroxyacetphenone is benzoylated to give o-benzoylacetophenone which undegoes isomerisation with a base which on acidification forms flavone

Chalcone method:

Chalcone method

Chalcone method:

Chalcone method O-hydroxyacetophenone on condensation with benzaldehyde or hydroxybenzaldehyde to give chalcone Chalcone is converted to flavone by three different ways

Wheeler method:

Wheeler method

Wheeler method:

Wheeler method It is a general method for the synthesis of flavones in which ring expansion of 2-benzylidenecoumaran3-ones take place.

Determination of structure of flavonols:

Determination of structure of flavonols Molecular formula of Flavonol is C 15 H 10 O 3 It contains one hydroxyl group On boiling with ethanolic solution of KOH, flavonol yield o-hydroxy benzoyl methanol and benzoic acid indicating that flavonol is 3 hydroxy flavone.

Determination of structure of flavonols:

Determination of structure of flavonols

Kostanecki method:

Kostanecki method

Kostanecki method:

Kostanecki method The appropriate o-hydroxyacetophenone is condensed with benzaldehyde or it’s derivative to give flavonone which is converted to flavonol

Robinson method:

Robinson method

Robinson method:

Robinson method In this method methoxyacetophenone or it’s derivative is condensed with the anhydride of a carboxylic acid or phenolic acid in the presence of potassium salt to form flavonol

Alagar-Flynn Oyamada method:

Alagar-Flynn Oyamada method

Alagar –Flynn Oyamada method:

Alagar –Flynn Oyamada method O-hydroxyacetophenone is condensed with benzaldehyde in the presence of alkali to form o-hydroxy chalcone which when treated further forms 3 hydroxy flavone which is dehydrogenated to flavonol.


Uses Flavoniods are also known as antispasmodics and diuretics plus they can stimulate the circulation and heart. Flavonoids are thought to lower blood pressure. Essential oils have long been noted for their ability to soothe and reduce stress lowering blood pressure. An oil maceration with added essential oils could prove to be quite desirable for massage especially with urban populations dealing with the cities’ pollution and high stress.


References Organic Chemistry of Natural products Vol 2- Gurdeep.R.Chatwal Organic Chemistry- Reactions and Reagents-O.P Aggarwal Chemistry of Natural Products- SV Bhat, BH Nagasampagi, M.Sivakumar Treas and Evans textbook of Pharmacognosy



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