Unit-II-Flavanoids.pptxaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

Anju Singh
School of Pharmaceutical Sciences,
CSJM University, Kanpur
1

UNIT-II
General introduction, composition, chemistry &
chemical classes, biosources, therapeutic uses and
commercial applications of following secondary
metabolites:
◦ Alkaloids: Vinca, Rauwolfia, Belladonna, Opium,
◦ Phenylpropanoids and Flavonoids: Lignans, Tea, Ruta
◦ Steroids, Cardiac Glycosides & Triterpenoids: Liquorice,
Dioscorea, Digitalis
◦ Volatile oils : Mentha, Clove, Cinnamon, Fennel, Coriander,
◦ Tannins: Catechu, Pterocarpus
◦ Resins: Benzoin, Guggul, Ginger, Asafoetida, Myrrh,
Colophony
◦ Glycosides: Senna, Aloes, Bitter Almond
◦ Iridoids, Other terpenoids & Naphthaquinones: Gentian,
Artemisia, taxus, carotenoids
2

 Second important class of the biphenylpropanoid derivatives
is known as the Flavonoids.
 polyphenolic compounds which are found in fruits, flowers,
seeds & vegetable.
 2000 different compounds reported to be present mostly
phenols either in the free state or as the glycosides
 flavous is a latin word yellow colour (yellow-coloured
compounds)
 They have a very limited role in this respect due to their low
toxicity when compared with other plant secondary
metabolites such as alkaloids.
 They are the pigments of flowers and attract pollinating
insects.
 They play a role in plant growth control by inhibiting &
activating enzymes.
3

 The flavonoids possess15 carbon atoms; two benzene rings
joined by a linear three carbon chain the skeleton can be
represented as the C6 - C3 - C6 carbon skeleton having a
pyran or chroman ring
 second benzene (aromatic) ring strategically positioned at
C—2, C—3 or C—4
 The three-carbon (-C3-) may be included through an oxygen
bond between the two phenyl rings into:
 1- A 5-membered heterocyclic ring (furan) as in aurones
 2- A 6-membered heterocyclic ring (pyran) to give flavonoids
constitute the largest group.
4
C
C
C
A
B
2
3
4
5
6
2'
3'
4'
5'
6'
O
1
2
3
4
5
6
7
2'
3' 4'
5'
6'
O
A
B
C
1
2
3
4
5
6
7
8 1'
2'
3'
4'
5'
6'

 flavones, flavanones, flavonols, isoflavones, and
 Anthocyanidins: colored aglycones found as a large number
of pigments from flower and fruits
 In certain specific cases either the 6-membered heterocyclic
ring (pyrones) is replaced by 5 membered heterocyclic ring
(aurones) or exists in an open-chain isomeric form
(chalcones)
 Apart from glycosylated derivatives, methylated, acetylated,
prenylated, or sulphated derivatives also exist
 Flavonoid aglycone : consists of benzene ring A, condensed
with 6 membered ring C pyran ring, which in 2nd position
carries phenyl ring B as a substituent
5
O
A
B
C
1
2
3
4
5
6
7
8 1'
2'
3'
4'
5'
6'

The flavonoid glycosides: Glycosides → aglycone
(non sugar part)+glycone (sugar part) When
glycosides are formed, the glycosidic linkage can be
located in positions 3 or 7 and may be L-rhamnose,
D- glucose, galactose or arabinose
6
O
A
B
C
1
2
3
4
5
6
7
8 1'
2'
3'
4'
5'
6'

Based on the carbon of the C ring on which B ring is
attached, and the degree of unsaturation and oxidation of the
C ring.
Flavonoids in which B ring is linked in position 3 of the ring
C are called isoflavones;
Those in which B ring is linked in position 4 – neoflavonoids
Flavonoids with open C ring are called chalcones.
Those in which the B ring is linked in position 2 further
subdivided into several subgroups on the basis of the
structural features of the C ring.
These subgroup are:
flavones, flavonols, flavanones, flavanonols, flavanols or
catechins and anthocyanins.
7

 Have a double bond b/w positions
 2 and 3 and a ketone in position 4 of the C ring.
 Most flavones of vegetables and fruits has a hydroxyl group
in position 5 of the A ring, while the hydroxylation in other
positions, for the most part in position 7 of the A ring or 3′
and 4′ of the B ring may vary according to the taxonomic
classification of the particular vegetable or fruit.
 Glycosylation occurs primarily on position 5 and 7,
methylation and acylation on the hydroxyl groups of the B
ring.
 Some flavones, such as nobiletin and tangeretin, are
polymethoxylated.
8
O
O

 Compared to flavones, they have a hydroxyl group in
position 3 of the C ring, which may also be
glycosylated.
 Again, like flavones, flavonols are very diverse in
methylation and hydroxylation patterns as well, and,
considering the different glycosylation patterns, they
are perhaps the most common and largest subgroup of
flavonoids in fruits and vegetables.
 For example, quercetin is present in many plant foods.
9
O
O
OH

 Flavanones (dihydroflavones)
 Have C ring saturated; unlike flavones, the double bond
between positions 2 and 3 is saturated. the only structural
difference between the two subgroups of flavonoids.
 The flavanones can be multi-hydroxylated, and several
hydroxyl groups can be glycosylated and/or methylated.
 Some have unique patterns of substitution, example:
furano-flavanones, prenylated flavanones, pyrano-
flavanones or benzylated flavanones, giving a great
number of substituted derivatives.
10
O
O

 Flavanonols
Flavanonols, also called dihydroflavonols, are the 3-hydroxy
derivatives of flavanones; they are an highly diversified and
multisubstituted subgroup.
 Isoflavones
As anticipated, isoflavones are a subgroup of flavonoids in
which the B ring is attached to position 3 of the C ring. They
have structural similarities to estrogens, such as estradiol, and
for this reason they are also called phytoestrogens.
 Neoflavonoids
They have the B ring attached to position 4 of the C ring.
11
O
O
OH
FLAVANONOLS
O O
Neoflavonoids
O
O
Isoflavones

 Flavanols or flavan-3-ols or catechins
Flavanols are also referred to flavan-3-ols as the hydroxyl
group is almost always bound to position 3 of C ring; they
are called catechins as well.
 flavanols to have two chiral centers in the molecule, on
positions 2 and 3, then four possible diastereoisomers.
 Epicatechin is the isomer with the cis configuration and
catechin is the one with the trans configuration. Each of
these configurations has two stereoisomers, namely, (+)-
epicatechin and (-)-epicatechin, (+)-catechin and (-)-
catechin.
(+)-Catechin and (-)-epicatechin are the two isomers most
often present in edible plants.
12
O
FLAVANOLS

 Another important feature of flavanols, particularly
of catechin and epicatechin, is the ability to form
polymers, called proanthocyanidins or condensed
tannins.
 The name “proanthocyanidins” is due to the fact that
an acid-catalyzed cleavage produces anthocyanidins.
Proanthocyanidins typically contain 2 to 60
monomers of flavanols.
 Monomeric and oligomeric flavanols
(containing 2 to 7 monomers) are strong
antioxidants.
13

 Anthocyanidins: Chemically, anthocyanidins are
flavylium cations and present as chloride salts.
 Only group of flavonoids that gives plants colors (all other
flavonoids are colorless).
 Anthocyanins are glycosides of anthocyanidins. Sugar
units are bound mostly to position 3 of the C ring and often
conjugated with phenolic acids, as in ferulic acid.
The color of anthocyanins depends on pH & also by
methylation or acylation at the hydroxyl groups on the A
and B rings.
 Chalcones
Chalcones and dihydrochalcones are flavonoids with open
structure; they are classified as flavonoids because they
have similar synthetic pathways.
14
O
OH
*
O

 If we consume food containing lignan precursor, it is
changed into enterolignans, enterodiol, enterolactone by
bacterial action residing in the colon
 enterodiol, enterolactone have weak estrogenic activity
& may exert action by non estrogenic mechanism
 enterodiol, enterolactone can mimic some actions of
estrogens- so plant derived lignan precursor are called as
Phytoestrogens
15
OH
OH
HO
OH
HO
OH
O
O
ENTERODIOL
ENTEROLACTO
NE

 1948- Haworth- introduced term- Lignan
 It is grp of dimeric phenylpropenoid
 Lignans – subgroup of non flavanoid polyphenols
 Based on C skeleton, cyclization pattern and the way O is
added in the skeleton they are divided into 8 types
 1. Furofuran 2. Furan 3. Dibenzylbutane
 4. dibenzylbutyrolactol 5. dibenzylbutyrolactone
 6. Aryltetralin 7. Arylnaphtalene
 8. dibenzocyclooctadienes
16

 de la Rosa L.A., Alvarez-Parrilla E., Gonzàlez-Aguilar
G.A. Fruit and vegetable phytochemicals: chemistry,
nutritional value, and stability. 1th Edition. Wiley J. &
Sons, Inc., Publication, 2010
 Han X., Shen T. and Lou H. Dietary polyphenols and their
biological significance. Int J Mol Sci 2007;9:950-988.
doi:10.3390/i8090950
 Manach C., Scalbert A., Morand C., Rémésy C., and
Jime´nez L. Polyphenols: food sources and bioavailability.
Am J Clin Nutr 2004;79(5):727-47
doi:10.1093/ajcn/79.5.727
 Tsao R. Chemistry and biochemistry of dietary
polyphenols. Nutrients 2010;2:1231-1246.
doi:10.3390/nu2121231
17

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