This document provides an overview of primary and secondary plant metabolites. It discusses starch, proteins, oils and fats as primary metabolites that plants produce for energy storage. As secondary metabolites, it covers glycosides, alkaloids, volatile oils, tannins, and bitter principles. For each type of metabolite, it provides examples of compounds and their characteristic chemical properties and biological activities. The document is intended as an introduction to the different classes of compounds produced by plant metabolism.

1. PHARMACOGNOSY
Lecture-4
(Introduction)
Dr. Ahmed Metwaly

2. Objectives
■ Types of metabolites

3. The Chemistry of Drugs
■ The living plant is nature’s laboratory. Therein are synthesized not only
chemical compounds that are utilized as food by man and animal as
starches, proteins and fats (Food storage products), but also other
compounds which are physiologically active and are known as “Active
Constituents = By-Products of Metabolism” of drugs.

4. ■ Primary Metabolic Products:
■ (1) STARCH
* Starch is the most common carbohydrate
present in the plant cells.
• It is formed by accumulation of glucose
molecules formed during photosynthesis.
• Pure starch is a white, tasteless and
odorless powder that is insoluble in cold
water or alcohol. It consists of two types of
molecules: the linear and helical amylose
( α(1→4) glycosidic bonds) and the
branched amylopectin (α(1→6) bonds).
* Chemically it is a polysaccharide of glucose
units with the general formula (C6H10O5)n

5. (1) Starch + I2 Blue
(2) Starch
(blue)
Dextrin
(purple)
dilute alkali or water
-amylase hydrolysis/ I2
(3) Starch acid hydrolysis
I2
glucose + maltose
(no color but reduces
Fehling's solution)
Chemical Test of Starch:
Uses of Starch
1) In dusting powder due to its absorbent properties.
2) Skin emollient (in mucilage forms).
3) Antidote for Iodine poisoning.
4) Tablet disintegrant.
5) Suspending agent.

6. ■ (2) PROTEINS
* Proteins are complex nitrogenous
compounds of high molecular weight.
* Chemically proteins are polypeptides of
amino acids (i.e. mixtures of amino
acid units joined together by peptide
linkages through elimination of water.
* Protein are stored by the plants usually
in the form of amorphous masses or
small particles called Aleurone grains.
* Protein usually present in the oily seed
e.g. Castor seed and Lin seed.

8. ■ Test for proteins (Microscopically)
1)Millon’s reagent stains proteins red on warming.
2)Picric acid stains proteins (ground and Crystalloid) yellow
3)Iodine solution stains the ground substance and crystalloid yellowish brown
leaving the globoid unstained

9. ■ Fixed oils and Fats
* They are esters of long
chain fatty acids of high
molecular weight. e.g.
Stearic, Oleic, Linoleic and
Recinoleic acids and
Glycerol.
In plants they are abundant in fruits and seeds e.g Olive oil,
Castor oil.
* In animals they are present in the form of complex lipids in
the brain and liver e.g. Cod liver oil and lard.
* Their consistency (Solids or Liquids), depends on the
proportion of esters of saturated (solid e.g Stearic acid) or
Unsaturated (Liquid e.g. Olieic acid) fatty acids.

10. ■ Characters of oils and fats:
1) Oils and fats are lighter than water, greasy in touch and leave a
permanent stain in paper.
2) Insoluble in water and alcohols except castor oil (sol. in alcohol)
3) Soluble in ether, chloroform and petroleum ether.
4) Stain red with Sudan III.
5) Easily saponified by aqueous solution of KOH yielding glycerol and salt of
acids (SOAPS).
6) Fixed oils are liquids at
normal temperature
(glycerides of unsaturated
fatty acid)
7) Fats are solids or semisolid
glycerides of saturated fatty
acids.

11. Uses of Fixed oils and fats:
A) Nutritive.
B) Pharmaceutically as solvents in intramuscular injections.
C) Preparation of soaps, Liniments, Plasters.
D) Laxatives, Demulcents, and Emollients.

12. ■ By-Products of Metabolism (Secondary metabolites):
■ Glycosides:
■ Are non-reducing organic compounds that on hydrolysis yield non sugar
part called aglycon or genin and one or more sugar unit(s) called glycon.
■ The usual glycosidic linkage between the sugar and aglycon
■ O-glycosides S- glycosides
N- glycosides C-glycosides

13. ■ Classification of glycosides according to the
aglycon:
■ Phenolic glycosides: e.g. arbutin in Uva ursi.
■ Alcohol glycosides: e.g. salicin in Salix bark.
■ Aldehyde glycosides: e.g. glucovanillin in vanilla
pods.
■ Coumarine glycosides: e.g. umbelliferone (7-
hydroxycoumarin) in Asafoetida and skimming
(umbelliferone-7-O-glucoside).

14. ■ Anthraquinone glycosides: e.g.
sennosides in Senna leaves, rhein in
Rhubarb, cascarosides in Cascara,
frangulin in Frangula and barbaloin in
Aloes. These compounds give
Borntraeger’s reaction.
■ Cyanophore (cyanogenic) glycosides: e.g.
amygdalin in Bitter almond and
linamarin in Linseed.
■ Sulphur (thio) glycosides or
Glucosinolates: e.g. sinigrin from black
mustard and sinalbin from white
mustard, alliin and allicin in Garlic and
Onion.
rhein
linamarin
sinigrin

15. ■ Saponin glycosides: e.g. glycyrrhizin from
Liquorice, senegin from Senega, Quillaia
saponins, , and Sarsaparilla saponins.
■ Flavonoid glycosides: e.g. diosmin in buchu
leaves, rutin and naringin from citrus fruit
peel. Flavonoids dissolve in alkalis giving
yellow color which on the addition of acid
becomes colorless.
glycyrrhizin
rutin

16. ■ Cardiac glycosides:
■ e.g. digitoxin in Digitalis leaves, scillarin in
Squill bulb and k-strophanthoside in
Strophanthus seeds.
* They are steroidal aglycon (Leibermann’s
test) attached to unsaturated lactone ring
(Baljet, Kedde’s tests).
* They contain 2-deoxy sugars, which gives a
positive Keller Killani test.
* They are two types:
a) Cardienolides e.g. Digitalis glycosides.
b) Bufadienolides e.g. Squill glycosides.
digioxin

17. ■ Alkaloids:
■ Alkaloids mean “alkali-like” referring to the basic nature of
these constituents. They are basic nitrogenous compounds
possess a physiological activity. The names of alkaloids end
in -ine to differentiate them from glycosides, which end in -in.
The basicity of alkaloids is usually due to amino nitrogen.
Alkaloids are generally insoluble in water and soluble in non
polar organic solvents. Being basic in chemical character,
they form water-soluble salts with acids.

18. ■ The physiological activities varies widely ; morphine
and codeine are analgesics, caffeine are cerebral
stimulant, atropine are mydriatics, physostigmine
and pilocarpine are myotics, reserpine are
hypotensive, cocaine are local anesthetic, quinine
are antimalarial, emetine are antiemetic, curare are
muscle relaxant, papaverine are antispasmodic,
ergometrine are uterine stimulant, colchicine are
antigout, ephedrine are decongestant.
morphine
caffeine
colchicineephedrineergometrine

19. ■ Volatile oils:
■ Are mixture of fragrant and odoriferous
principles found in various parts of
plants. They are volatile with steam,
and usually immiscible with water, and
are known as essential oils or ethereal
oils. They differ from fixed oils in that,
being capable of volatilization, they do
not leave a permanent stain on filter
paper, and do not consist of glyceryl
esters of fatty acids, but they are
terpenoids, they can not be saponified
with alkalis, do not become rancid as
fixed oils, but on exposure to light and
air they will oxidize and resinify. e.g. of
drugs rich in volatile oil are mentha,
buchu, eucalyptus, orange, lemon,
rose, anise, fennel, etc.

21. ■ Tannins:
■ Compounds of high molecular weight which
were able to precipitate proteins from
solution and have the property of combining
with proteins rendering them resistant to
proteolytic enzymes and convert them into
leather. This action when applied to living
tissue is known as astringent action. So
tannins are used in medicine as astringents
both to the gastro-intestinal tract and on
skin abrasions. In industry tannins are
employed in the manufacture of leather and
ink.
catechol tannin
Tannic acid

22. ■ Chemically, tannins are complex substances which may be classified as
to whether they yield catechol or pyrogallol on decomposition when
heated to 180-2000c. e.g. of pyrogallol tannins; rhubarb, clove,
hamamelis, tea, oak galls, oak nut, chest nut tannins. They give bluish-
black color with ferric chloride, and give no precipitate with bromine
water. e.g. of catechol tannins; cinchona, cinnamon, hamamelis, tea,
cassia, cutch, Gambier. They give greenish-black color with ferric chloride,
and produce a precipitate with bromine water.

23. ■ Bitter Principles:
■ Are mostly vegetable compounds composed of C, H, and O, but
are free from nitrogen and non-hydrolysable i.e. they belonging
neither to the alkaloids nor to the glycosides and are
heterogeneous compounds of bitter taste.
■ It can be classified into phenolic b. p. e.g. humulone and
lupulone, lactone b. p. e.g. santonin, from santonica flowers,
chromone b. p. e.g. khellin and visnagin from Ammi visnaga
fruits, and coumarine b. p. e.g. xanthotoxin and imperatorin
from Ammi majus fruits.

24. QUESTIONS?