Introduction_to_Secondary_Metabolites_of_Plants

Introduction to
Secondary Metabolites
DR. SIDDHI UPADHYAY
H.O.D. & ASSOCIATE PROFESSOR
Dept. of pharmacognosy and phytochemistry
SIGMA INSTITUTE OF PHARMACY

Content
Definition, classification, properties and test for
identification of :
• Alkaloids
• Glycosides
• Flavonoids
• Tannins
• Volatile oil
• Resins

• In plants, there are primary and secondary metabolites
produced after metabolism.
• Primary metabolites are useful to plants, as well as to
humans.
• While secondary metabolites are not useful to plants, but very
much important to humans in treatment and prevention of
various diseases.
• Primary metabolites include
o Carbohydrates
o Lipids
o Proteins
• Secondary metabolites include
o Alkaloids
o Glycosides
o Flavonoids
o Tannins
o Volatile oil
o Resins

Definition
• Alkaloids are naturally occurring organic substances,
predominantly found in plant sources including marine
algae and rarely in animals ; contain at least one
nitrogen atom in heterocyclic ring ; basic in nature
and so referred the term alkaloid (alkali-like); possess
remarkable physiological action on human when given
in small quantity.

Definition
• Organic natural compounds present in a lot of plants and some
animals, these compounds upon hydrolysis give one or more sugars
(glycone) moieties and non sugar (aglycone) moietyd
• Glycoside=sugar group+ nonsugar group
(glycone) (aglycone or genin)
• Glycone and aglycone are linked by glycosidic linkage

• Aglycone portion is responsible for pharmacological
action on body.
• While glycone portion is helping the aglycone moiety
penetrating in the cell.

Identification tests
• Anthraquinone Glycosides (eg. Aoe, senna)
o Borntrager’s test
o Modified borntrager’s test
o Micro-sublimation test
• Cardiac Glycosides (eg. Digitais, theetia, scilla)
o Cardenolides
• Legal test
• Baljet test
o Bufedienoides
• Libermann burchard test
o Deoxy sugars
• Keller-kiliani test
o 3,5-dinitro benzoic acid test

• Cynogenetic Glycoside (eg. Linseed, bitter almond)
o Grignard reaction (Sodium picrate test)
• Flavonoid Glycosides (eg. Rue)
o Ammonia test
o Shinoda test
o Vanillin HCl test
• Saponin Glycosides (eg. Licorice, shatavari)
o Haemolysis test
o Foam test
o Libermann burchard test (for triterpenoid)
• Coumarin Glycosides (eg. Psoralea)
o FeCl3 test
o Fluorescence test

• Reducing sugars (eg. Agar, acacia, honey)
o Fehling’s test

• Chemically,
they are the compelx mixtures of
1. resin acids
2. resin alcohols (resinols)
3. resin phenols (resinotannols)
4. resin esters
5. resenes

Definition
• 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).

• However, their occurence is not restricted to flowers but
include all parts of the plant.
• They are secondary metabolite and effective in CNS
disorders.

Classification
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

Antioxidant flavonoids
• Quercetin (a flavonol in vegetables, fruit
skins, onions)
• Xanthohumol (a prenylated chalcone in
hops and beer)
• Isoxanthohumol (a prenylated
flavanone in hops and beer)

Properties
• The capacity of flavonoids to act as antioxidants
depends upon their molecular structure. The position of
hydroxyl groups and other features in the chemical
structure of flavonoids are important for their antioxidant
and free radical scavenging activities.
• The antioxidant properties of the prenylflavonoids were
compared to those of quercetin (a flavonol), genistein
(the major isoflavone in soy), chalconaringenin (a
nonprenylated chalcone), naringenin (a nonprenylated
flavanone), and vitamin E.

• A flavonoid chalcone (chalconaringenin) and a flavanone
(naringenin) with no prenyl groups act as prooxidants,
i.e. they promote rather than limit the oxidation of LDL by
copper. However, adding a prenyl group to these
flavonoid molecules counteracted their prooxidant
activities.

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).
O O
OHOH
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

Identification tests
• 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.

THANK YOU !!!
siupa.pharma@gmail.com

Introduction_to_Secondary_Metabolites_of_Plants

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