2. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 1
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
ALKALOIDS
Definition:
Alkaloids may be defined as basic nitrogenous compounds which occur abundantly in the
plant kingdom. They contain one or more nitrogen usually in a heterocyclic ring and have a
marked physiological action on man & animals. The nitrogen may exist as primary (1◦ amines),
secondary (2◦ amines) or tertiary (3◦ amines) amine. These compounds are basic but the degree
of their basicity depends on the structure of the molecule and presence and location of other
functional groups.
Examples:
Nicotine Atropine
Functions of Alkaloids in plants:
The possible functions of alkaloids in plants are:
1. They are poisonous agents that protect the plants against insect & herbivores.
2. Alkaloids are reserve substances capable of supplying nitrogen or other necessary elements to
the plant.
3. They may regulate growth/work as growth regulatory factor.
4. They are end product of detoxification reactions representing a metabolic locking-up of
compounds otherwise harmful to the plant.
Properties:
Most alkaloids are well defined crystalline solids and they unite with acids to form
salts. In the plants they may exist in the Free State or as alkaline salts.
The alkaloids are usually insoluble or sparingly soluble in water but their salts with
acids are freely soluble in water.
The free alkaloids are soluble in Ether, Chloroform or other non-polar solvents in
which the salts are insoluble.
This property now permits a ready mean for the isolation and purification of alkaloids.
The alkaloids usually possess a bitter taste.
Md.
Imran
Nur
Manik

3. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 2
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
Pharmacological actions:
The alkaloids have a wide range of pharmacological actions:
Sl Physiological Action Alkaloids
1 Analgesic & narcotic Morphine, Codeine
2 CNS stimulant Strychnine
3 Mydriatic Atropine
4 Miotic/Glaucoma Pilocarpine
5 Hypertensive Ephedrine
6 Antihypertensive Reserpine
7 Antineoplastic/anticancer Vinblastine, Vincristine
8 Emetic Emetine, Sanguinarine
9 Cardiac arrhythmia/dysrhythmia Quinidine
10 Skeletal muscle relaxant (+)-Tubocurarine
11 Oxitocic Ergonovine (also known as Ergometrine) and it’s
derivatives
Test for Alkaloids:
Most alkaloids are precipitated from neutral or slightly acid solutions by various re-agents.
The precipitate may be amorphous or crystalline and are of various colours such as:-
Re-agents Colors of ppt
1. Mayer’s re-agent
(Potassium mercuric iodide solution)
Cream
2. Wagner’s re-agent
(Solution of iodine in KI)
Reddish brown
3. Dragendoff’s re-agent
(Solution of potassium bismuth iodide)
Reddish brown
4. Hager’s re-agent
(Saturated solution of picric acid)
Yellow
Classification:
Alkaloids may be classified in a number of ways. For example: they may be classified
according to source, chemical structure or pharmacological actions etc. Each system has its
advantages and disadvantages.
Usually they are classified on the basis of the ring structure or nucleus of the alkaloids as
follows
1. Pyridine-Piperidine group
2. Tropane group
3. Quinoline group
4. Isoquinoline group
5. Indol group
6. Imidazole group
7. Steriodal group
8. Alkaloidal amino group
9. Lupinane group
10.Purine group
Md.
Imran
Nur
Manik

4. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 3
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
(1) Pyridine-Piperidine group:
The alkaloids in this group contain Pyridine or Piperidine in the molecule. The important
alkaloids in this group are Nicotine, Coniine, Arecoline, Lobeline etc.
Pyridine Piperidine Nicotine Coniine
Nucleus Examples
(2) Tropane alkaloids:
Tropane is a dicyclic compound where both Pyrrolidine and Piperidine ring systems are
present. The important alkaloids in this group are Atropine, Hyoscyamine, Hyoscine
(scopolamine) etc.
Pyrrolidine Piperidine Tropane
Example:
Atropine
(3) Quinoline alkaloids:
Alkaloids containing the Quinoline ring as the principal nucleus are Quinine, Quinidine,
Cinchonine, Cinchonidine etc.
Quinoline
(Nucleus)
Example: Quinine
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5. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 4
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
(4) Isoquinoline alkaloids:
The Isoquinoline ring occurs in a number of alkaloids in widely separated plant families.
For example: Papaverine, Morphine, Emetine etc.
Isoquinoline
(Nucleus)
Example: Papaverine
(5) Indole alkaloids:
A number of important alkaloids possess an indole ring in their structure. For example:
Strychnine, Reserpine, Brucine, Vinblastine, Vincristine etc.
Indole
(Nucleus)
Example: Reserpine
(6) Imidazole alkaloids:
Imidazole ring occurs in the alkaloids Pilocarpine, Isopilocarpine etc.
Imidazole
(Nucleus) Example: Pilocarpine
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Manik

6. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 5
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
(7) Steroidal alkaloids:
The steroidal alkaloids are characterized by the cyclopentanoperhydrophenanthrene (CPP)
nucleus. The important alkaloids are Protoveratrine A & B, Aconitine, Conessine etc.
CPP(Nucleus) Example: Conessine
(8) Alkaloidal amino group:
The alkaloids in this group do not contain heterocyclic nitrogen atoms. For example:
Colchicine. Some are derivatives of Phenylethylamine like Ephedrine, Mescaline etc.
Phenylethylamine
(Nucleus) Example: Ephedrine Mescaline
(9) Lupinane alkaloids:
The alkaloids in the group contain a dicyclic Lupinane structure/ring. For example
Sparteine, Lupinine etc.
Lupinane
Nucleus Example: Lupinine
Md.
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Manik

7. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 6
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
(10) Purine alkaloids:
The alkaloids in this group contain the Purine nucleus which consists of the six membered
Pyridine ring fused to the five membered Imidazole ring. The important examples in this group
are Caffeine, Theobromine etc.
Purine
Nucleus Example: Caffeine
Extraction of alkaloids
Process I
Powdered materials
Free alkaloids and other plant constituents
Organic layer containing Aqueous layer containing
alkaloids and other plant water soluble compounds
constituents
Aqueous layer containing Organic layer containing
alkaloidal salts other organic compounds
Precipitation of free alkaloids
Moisten with aqueous alkali (like Sodium
carbonate, Sodium bicarbonate or Lime)
Extract with organic solvent
like Benzene, Chloroform etc)
Extract with dilute acid
Add aqueous alkali
Md.
Imran
Nur
Manik

8. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 7
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
Description:
The powdered material is moistened with aqueous alkali [water and mixed with lime which
combines with acids, tannins and other phenolic substances and sets free the alkaloids (if they
exist in the plant as salts)]. The alkaloids are set free with other plant constituents. Extraction is
then carried out with organic solvents such as Benzene or chloroform (ether or petroleum
spirit). The concentrated organic liquid which contains alkaloids and other plant constituents is
then shaken with dilute acid (aqueous acid) and allowed to separate. Alkaloid salts are now in
the aqueous liquid, while many impurities remain behind in the organic liquid. Aqueous alkali
is added to the aqueous layer giving precipitation of free alkaloids.
Process II
Powdered materials
Moisten with water or aqueous alcohol
Containing dilute acids.
Alkaloidal salts and other plant constituents
Extract with organic solvent like
Benzene, Chloroform etc.
Aqueous layer containing organic layer containing
Alkaloidal salts. Pigments and other
Organic compounds.
Add aqueous alkali
Precipitation of free alkaloids
Description:
The powdered material is extracted with water or aqueous alcohol containing dilute acid.
We get Alkaloidal salts and other plant constituents. Pigments and other unwanted materials
are removed by shaking with chloroform or other organic solvents. Then we get aqueous layer
containing Alkaloidal salts. The free alkaloids are then precipitated by the addition of aqueous
alkali (excess sodium bicarbonate or ammonia) and separated by filtration or by extraction with
organic solvents.
Md.
Imran
Nur
Manik

9. Alkaloids: Pharmacognosy
Prepared By: Shadid Uz Zaman At Tadir; B.Pharm.; M.Pharm.; DU Page 8
Arrangement: Md. Imran Nur Manik; B.Pharm.;M.Pharm.; RU
The important characteristics/features of alkaloids
The important characteristics/features of alkaloids are
1. They are complex chemical compounds of plant origin.
2. In addition to Carbon and Hydrogen they all contain Nitrogen and generally also
Oxygen.
Exceptions: Coniine, Nicotine and Sparteine do not contain Oxygen.
3. The Nitrogen atom usually exists in a heterocyclic ring.
Exceptions: Colchicine, Ephedrine etc.
4. Most of the alkaloids are crystalline solids, though a few are amorphous.
Exceptions: Coniine, Nicotine and Sparteine are liquid.
5. Alkaloids are usually colorless compounds.
Exceptions: Betaine is red, Berberine is yellow.
6. Alkaloids are either insoluble or sparingly soluble in water.
Exceptions: Colchicine is soluble in water. Caffeine is soluble in hot water.
7. Alkaloidal salts are readily soluble in water but insoluble in organic solvents.
Exception: Quinine sulphate is sparingly soluble in water.
8. Most alkaloids are physiologically active.
Exception: Ergotaminine.
9. Most of them are precipitated by Dragendorff’s, Mayer’s, Wagner’s and Hager’s reagent.
Exception: Caffeine.
10. In plants, alkaloids usually exist in the form of salts of simple organic acids, such as
Lactic, Malic, Tartaric or Citric acids.
Exceptions: Some alkaloids exist as glycoside e.g. Solamine, Tomatine etc.Md.
Imran
Nur
Manik