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FLAVONOIDS General characteristic 1
Plan
1. The general characteristic
of flavonoids
2. Physical and chemical
properties of flavonoids
3. Qualitative and
quantitative determination
of flavonoids
Flavonoids are the largest group of naturally occurring
phenols and occur in the plant both in the free state and
as glycosides.
They may be described as a series of C6-C3-C6
compounds.
Classification
The largest group of flavonoids is characterized by the
presence of a pyran ring linking the three carbon chain
with one of the benzene rings.
The numbering system for these flavonoid derivatives is as
follows:
AB
6' 5'
4'
3'2'
1'
8
7
6
5 4
3
21
CB
A
O
3
Flavonoids are distinguished by the
place of B-ring location :
O
AB
C
Isoflavonoids
6' 5'
4'
3'2'
1'
8
7
6
5 4
3
21
CB
A
O
True flavonoids
O
A
B
C
Neoflavonoids
4
True flavonoids are classified according to the
oxidation level of the propane moiety of the
molecule.
O
OH
O
OH
OH
O
OH
+
O
O
O
O
OH
O
O
OH
O
O
OH
O
O
O
CH
Catechins Leucoanthocyanidins
Anthocyanidins
Flavanones Flavanonoles
Flavones Flavonoles Aurones
Chalcones
5
ISOFLAVONOIDS
6
O O
O
O
OH
OH
O
O
O
O O
7
10
9
8
O11
3
2
1
4O5
O
A B
C D
6a
11a 12
O7
O5
68
9
10
11
1
2
3
4
A
BCD
6a
12a
O
O
A B
C D
6a
11a
Simple isoflavonoids
Isoflavan Isoflavanone Isoflavanol
Isochalcone Isoflavone 3-arylcoumarin
Condensed isoflavonoids
Coumestane Rotenoid Pterocarpane
THE MOST WIDE-SPREAD COMPOUNDS
Flavonoles
Apigenin
OOH
OH
OOH
OOH
OH
OH
OOH
Luteolin
OOH
OH
O CH3
OOH
Diosmetin
Kaempferol
OOH
OH
OH
O
OH
OOH
OH
OH
OH
O
OH
Quercetin
OOH
OH
OH
OH
O
OH
OH
Myricetin
Isorhamnetin
OOH
OH
O CH3
OH
O
OH
Flavones
O
OH
OH
OH
O
OH
CH3O
Rhamnetin
7
Flavonoid glycosides Rutin, Hyperoside, Quercetrin
Flavonoids are widely distributed in nature either
in a free state or linked to sugars, which are more
common in higher plants and in young tissues,
where they occur in the cell sap.
Flavonoids are of abundant in the Polygonaceae,
Rutaceae, Fabaceae, Rosaceae.
O
OOH
OH
OH
OH
O-Gala
O
OOH
OH
O-Rha
OH
OH
8
Rutin Hyperoside Quercetrin
O
OOH
OH
OH
Glu
Vitexin
BIOSYNTHESIS:
Flavonoids are products from a cinnamoyl-CoA
(C6C3, precursor from the shikimate pathway)
starter unit, with chain extension using three
molecules of malonyl-CoA.
Flavonoids are therefore of mixed biosynthesis,
consisting of units derived from both shikimate
and acetate pathways.
9
10
The triketide starter unit undergoes cyclization
by the enzyme chalcone synthase to generate the
chalcone group of flavonoids. Cyclization can
then occur to give a pyranone ring containing
flavanone nucleus, which can either have the
C2-C3 bond oxidized (unsaturated) to give the
flavones or be hydroxylated at position C3 of the
pyranone ring to give the flavanonol group of
flavonoids. The flavanonols may then be further
oxidized to yield the anthocyanins, which
contribute to the brilliant blues of flowers and
the dark colour of red wine.
11
FUNCTIONS IN PLANTS
Control of the plant growth;
Inhibiting and activating the enzymes;
Having a role in the biochemistry of
reproduction;
Fungicidal properties;
Protect the plant from parasites’ attack;
12
These compounds have high ecological
importance in nature as colour attractants to
insects and birds as an aid to plant pollination.
The flavonoids contribute to many other colors
found in nature, particularly the yellow and
orange of petals; even the colourless flavonoids
absorb light in the UV spectrum (due to their
extensive chromophores) and are visible to
many insects. [A chromophore is the part (or moiety) of
a molecule responsible for its color].
13
PHYSICAL AND CHEMICAL
PROPERTIES
Flavonoids are crystalline compounds;
They are colored:
• yellow: flavones, flavonoles, chalcones, aurones;
• red: anthocyanidins in acidic media;
• blue: anthocyanidins in alkaline media;
• colorless: catechins, flavans, flavanones,
leucoanthocyanidins, isoflavones.
Flavonoid glycosides are generally soluble in water and
alcohol but insoluble in organic solvents; the aglycones
(genins) are only sparingly soluble in water but soluble
in ether, chloroform.
Under the UV light flavonoids show fluorescence
ofdifferent colors (yellow, orange, brown, red). 14
Certain flavonoids also markedly affect the taste
of foods: for example, some are very bitter and
astringent such as the flavanone glycoside
naringin, which occurs in the peel of grapefruit
(Citrus paradisii). Interestingly. the closely
related compound naringin dihydrochalcone,
which lacks the pyranone ring of naringin, is
exceptionally sweet, being some 1000 times
sweeter than table sugar (sucrose).
15
IDENTIFICATION 1. Chromatographic
identification
Fluorescence under filtered UV light
is used to differentiate different
groups of these compounds as
follows:
AlCl3 gives yellow color (flavones,
flavonoles, chalcones, aurones).
Under the UV light these
compounds show fluorescence of
different colors, e.g.
flavones – green;
Flavonoles – yellowish to yellowish-
green;
Chalcones – brown-pink;
Aurones – pale-brown.
16
1 – rutin, 2 – chlorogenic
acid, 3 – quercetin in
ginkgo leaves samples and
tinctures
2. Shinoda’s test (cyanidin reaction) The alcoholic solution of flavone or flavonol when treated with metallic
magnesium (or Zinc) and hydrochloric acid gives an orange, red or
violet color
3. Wilson’s reaction. Flavonoids form complexes with boric acid which is
not destroyed by addition of citric acid alcoholic solution (or oxalic
acid).
O
C C
OB
O O
O
O O
OH
OH
OH
OH
17
O
O
OH
O H
O H
O H
O H
OOH
O H
O H
O H
O HO HH
OOH
O H
O H
O H
O H
H +
- H 2 O
+
C l-
Q u e r c e t i n Q u e r c e t i n c h r o m e n o l C y a n i d i n c h l o r i d e
4. A reaction with alkal isolution. Flavonoids
(flavones, flavonoles, chalcones, aurones) when treated
with alkali solution give yellow or orange color.
5. Reaction with iron (III) chloride.
Flavonoids (flavones, flavonoles, chalcones, aurones)
when treated with iron (III) chloride solution give
green or violet color.
6. Reaction with vanillin and concentrated
hydrochloric acid.
Catechins when treated with vanillin solution in
hydrochloric acid give red color.
18
O
O
OH
OH
OH
OH
OH
O
O
OH
OH
OH
OH
ONa
NaOH
OO
O O
OH
OH
OH
OHFe
Cl
OOH
OH O
OH
OH
OH
OH
OOH
OH O
OH
O
O
O
Fe+FeCl3 +FeCl3
Green colour Violet colour
QUANTITATIVE DETERMINATION
Spectrophotometric
High performance liquid chromatography
Gravimetric
Titration
Fluorometric
Polarographic
19
USES
Flavonoids have important dietary significance
because, being phenolic compounds, they are
potent antioxidants.
Many disease states are known to be exacerbated
by the presence of free radicals such as
superoxide and hydroxyl, and flavonoids have the
ability to scavenge and effectively ‘mop up’ these
damaging oxidizing species.
Flavonoids contribute to the diuretic and
diaphoretic action of such drugs as chamomile,
elder flowers, linden blossoms, horsetail and
others
The isoflavone derivatives have a distinct
estrogenic effect.
20
Foods rich in this group of compounds have
therefore been proposed to be important in
ameliorating diseases such as cancer and heart
disease (which can be worsened by oxidation of
low-density lipoprotein); quercetin, a flavonoid
present in many foodstuffs, is a strong
antioxidant. Components of milk thistle (Silybum
marianum), in particular silybin, are
antihepatotoxins; extracts of milk thistle are
generally known as silymarin.
O
OH
OOH
HO
OH
OH
Quercetin
OO
O
HO
OH O
OH
OCH3
OH
OH
Silybin
O
OH
OOH
HO
OH
OH
Quercetin
OO
O
HO
OH O
OH
OCH3
OH
OH
Silybin 21
Literature
1. Pharmacognosy / ed. by prof. Kyslychenko V.S.
Kharkiv/ NUPh, “Zoloti storinky”. – 2011. – 600 p.
2. Trease G.E., Evans W.C. Pharmacognosy. - London;
Philadelphia; Toronto: Sydney; Tokyo; WB Saunders,
1996. - 832 s.
3. Tyler V.E., Brady L.R., Robbers J.E. Pharmacognosy,
9-th ed. - Leo and Fabiger. Philadelphia, 1988.-856 p.
4. British Herbal Pharmacopoeia / British Herbal
Medicine Association.- London, 1996. – 212 p
5. European Pharmacopoeia - Fourth edition. - counsel of
Europe, Strasbourg, 2001
6. Практикум по фармакогнозии: учебное пособие для
студ. вузов / под ред В.Н.Ковалева. – Х: Изд-во
НФАУ, Золотые страницы, 2003. - 512 с.
