Contents:
Introduction
• Isolation
• Test for determination
• Genei•al iiictliod of structural deter%nation
• Structttral elucidation o£ qricrcctin

• Flavonoids are a group of polyphenolic compounds, diverse in
chemical structure and characteristics, found ubiquitously in
plants.
• Flavonoids (or biofiavonoids) (from the Latin
word flavus meaning yellow, their color in nature) are a class
of plant secondary metabolites.
• Over 4,000 different flavonoids have been identified within the
major flavonoid classes which include flavonols, flavones,
flavanones, eatechins, anthocyanidins, isoflavones,
dihydroflavonols, and chalcones.

• Flavonoids constitute one of the most characteristic classes of
compounds in higher plants.
• Flavonoids are found in higher vascular plants, particularly in
the flower, leaves and bark. They are especially abundant in
fruits, grains and nuts, particularly in the skins.
Many flavonoids are easily recognized as flower pigments in most
angiospcrm families (flowering plants).
However, their occurrence is not restricted to flowers but include all
p sof hcplann
• Beverages consisting of plant exkacts (beer, tea, wine, knit
juice) are the principle soume of dietary fiavonoid intake.

Class
Flavanol
Flavonoid
(+)-Catechin
(-)-Epicateckin
Epigallocatehin
Chrysin, apigcnin
Dietary source
Tea
Flavour
Flavonol
Rutin, luteolin, and Fruit skins, red wine, buckwheat,
luteoltn glucosides red pepper, and tomato skin
Kaempferol, quercetint Onion. red wine, olive oil,
myricetin. and tamarixetin berries, and grapefruit.
Flavanone
lsoRavone
Anthocpnidn
Naringin, naringenin, taxifolin,
and hesperidin
Genistin, daidzin
Apigenidin, cyanidin
Citrus fruits. grapefruits, lemons,
and omnges
Soyahean
Cherry, easberry, and stmwberry

• Flavonoids (particularly glycosides) can be degraded by enzyme
action when collected plant material is fresh or non-dried.
• lt is thus advisable to use dry, lyophilized, or frozen samples.
• When diy plant material is used, it is genemlly ground into a powder.
• For extraction, the solvent is chosen as a function of the type of
• flavonoid required and hence polarity is an important considemtion
here.
• Less polar flavonoids (e.g., isoflavones, flavanones, methylated
flavours, and flavonols) are extracted with chloroform,
• dichloromcthane, diethyl ether, or ethyl acetate,
• While flavonoid glycosides and more polar aglycones are extracted
with alcohols or alcohol—water mixtures.
• Glycosides have increased water solubility and aqueous alcoholic
solutions are suitable.

Plant material
(Fla›'one/Fixvanol)
hot »’atcr
Aqueous extract
Remiive tannins
Sugat free
(Flnvone/Flsv»nol
Scid
qificd ith HCP
Aqueous phase
Fractional
Alcoholic phase
(Flat one/Flavaool)
Desired
Oamnoid

• Sblnoda test: To the ethanolic extract + added four pieces of magnesium
fillings (ribbon) + few drops of concentrated HCI. A pink or red colour
indicates the presence of flavonoid.
- orangc to red indicated flavones,
— red to pink indicated flavonoids,
- pink to magenta indicated flavononcs.
• Sm4lombydrofdetef:toU:caquoouscxtact+addI0%aqucouxsodum
hydroxide. This gives a yellow color. A change in color from yellow to
colorless on addition of dilute HCI is an indication for the presence of
Savonoidv
• p-Dlnietbyfnmlnoclnnainaldehyde test: A colorimetric assay based upon
the reaction of A-rings with the chromogen p-
dimcthylaminocinnamaldehyde (DMACA) has been developed for
flavanoids in beverages that can be compared with the vanillin procedure.

General method of determination of
flavones
• The no. of OH group is estimated by the usual methods =>
Flavone does not contain any —OH group.
• On fusion with alkali, flavones are degraded to a phenol and
aromatic acids. Ex:-
Flax’oncs Phcnol
COWJ*tCGC/

• Flavones on boiling with KOH gives four
diPerent products

Backer Venkutrumans method
• Finally the stmcture proposed by degradation
method is proved by it synthesis.
Robinson’s metbod

Determination of structure of
Flavonols
• Same iiianner as that of flavone
• The lxOl formula is C„H 1,) O,
• It contains one hydroxyl group as indicated by
usrial methods.
• On boil wltli ethanolic solutlon of KOH,
Flavonol yields, O- Hydroxy benzoylinetlianol
and benzoic acid indicates that Flavonol is 3-
hydroxy flavone.

• Flnally the structure of flavonols are conflnned
by its synthesis -Roblnsons method

Rhamnose
• Widely distributed pigments occurs as rhamnosides (quercitine) in
the bark of Quercus tinctoria.
HCI
+
• Mol formula is CASHJ oO7
• It was found to contain four hydroxyl groups as it forms penia-
acetyl and pentamethyl group.
• On fusion with KOH, it gives Phloroglucinol + protocatechuic acid-
it indicates that quercetine is 5,7,3’,4’ — tenahydroxy flavonol .
t JH
Quercitin
Huercitine

• The structure was further supported by the fact that on boiling
with alcoholic potash pentamethyl quercetin gives 6-OH,
m,2,4-trimethyl acetophenone and veratric acid.

The structwe was further supported by iG synlesis from
Kostaneck'e Synthesis using ,2,4 dimc1oxy,6-hydroxy
acetophenonc and 3,4-dimethoxy benzaldehyde as starting
materials
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