Alkaloids: Distribution, properties, tests, extraction, structural types and classification.

1. Pharmacognosy-I

2. A precise definition of the term 'alkaloid'((alk=alkali and oid=like i.e. alkali-
like) is somewhat difficult because there is no clear cut boundary between
alkaloids and naturally occurring complex amines
Introduction
Coniine
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3. Distribution
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4. Plant Part Drug ( Alkaloids) Plants
Whole aerial plant Lobeline, Tylophorine, Ephedrine Lobelia. Tylophora. Ephedra
Seeds Strychnine, Physostigmine,
Colchicine
Nux vomica. Physostigma,
Colchicum
Rhizomes & Roots Emetine, Reserpine, Aconitine Ipecac, Rauwolfia, Aconite
Bark Conessine, Cinchonine Kurchi, Cinchona
Fruit Piperine Black pepper
Leaves Scopolamine, Atropine, Ecgonine Datura, Belladonna, Coca
Stem Anaferine Withania
Flowering buds Hyoscyamine Hyoscyamus
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5. Properties of alkaloid
Alkaloids exhibit a variety of physical and chemical properties
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6. Chemical Properties of alkaloid
Alkaloids possess carbon, hydrogen and nitrogen and in
most cases oxygen as elements.
Alkaloids usually contain one nitrogen atom, although
some, like ergotamine, may contain up to 5.
The nitrogen may exist as a primary amine (RNH), as
a secondary amine (R2NH), or as a tertiary amine (R3NH).
Like basic compounds they form their crystalline salts with
acids like hydrochloric acid, sulphuric acid, citric acid, and
tartaric acid.
On treatment with phosphotungstic acid, phosphomolybdic
acid, picric acid, potassium mercuri-iodide and tannic
acid, they yield insoluble precipitates (double salts)
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7. Pharmacological Action of Alkaloid
Activity Alkaloids
Analgesic & Narcotic Morphine and Codeine
CNS-stimulant Caffeine, Strychnine & Brucine
Cardiac depressant Qinidine
Mydriatic Atropine & Hematropine
Miotic Physostigmine, Pilocarpine
Hypertensive (BP) Ephedrine
Anti-Hypertensive Reserpine
Anti cancer Vincristine, Vinblastine
Antimalarial Quinine
Diuretic Theobromine, Theophylline
Antiamoebic & Emetic Emetine, Sanguinine
Anticholinergic Atropine, hyoscyamine
Antitussive Codeine, Noscapine
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8. Why alkaloids occur in the plants?
In plants alkaloids act as poisonous and stimulating agents.
1. They may act as protective against insects and herbivores due to their
bitterness and toxicity. For e.g. Nicotine and anabasine act as powerful repellents for
many insect groups and thus protects plants from insects and herbivorous.
2. They function as reserve substances for nitrogen and supply it as well as
other elements necessary for the plant's economy.
3. They sometimes, act as growth regulators in certain metabolic systems.
4. They are end product of detoxification reactions representing a metabolic
locking up of harmful substances for the plant.
5. They occur as pigments, such as pteridine and betalains, and attract
animals for pollination.
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9. Classification of Alkaloids
There are various schemes for the classification of alkaloids. Widely accepted
classification system is as:
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10. Based on the ring structure or nucleus of the chief alkaloid group in the plant
drug are classified as follows: (1) , (2)
Alkaloids Ring Examples
Pyridine-piperidine
The alkaloids in this group
contain Pyridine or
Piperidine in the
molecule
Pyridine-piperidine Nicotine Coniine
Tropane
Tropane is a dicyclic
compound where both
Pyrrolidine and Piperidine
ring systems are present Pyrrolidine-piperidine- Tropane Atropine
+e.g. lobelia alkaloids, lupine alkaloids,
+e.g. hyoscyamine and scopolamine,
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11. On the basis of nucleus/ Ring structure (3) , (4)
Alkaloids Ring Examples
Quinoline
The alkaloids in this group
contain Quinoline ring as
the principal nucleus
Quinoline Quinine
Isoquinoline
The Isoquinoline ring
occurs in a number of
alkaloids in widely
separated plant families Isoquinoline Papaverine
+e.g. Quinidine, Cinchonine, Cinchonidine ,
+e.g. Morphine, Emetine ,
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12. On the basis of nucleus/ Ring structure (5) , (6)
Alkaloids Ring Examples
Indole
A number of important
alkaloids possess an
indole ring in their
structure
Indole Reserpine
Imidazole
The Imidazole ring occurs
in the alkaloids.
Imidazole Pilocarpine
+e.g. Strychnine, Brucine, Vinblastine, Vincristine
+e.g. Isopilocarpine,
Reserpine
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13. On the basis of nucleus/ Ring structure (7) , (8)
Alkaloids Ring Examples
Steroidal
The steroidal alkaloids
are characterized by the
cyclopentanoperhydro
phenanthrene (CPP)
nucleus.
CPP
Conessine
Lupinane
The alkaloids in the group
contain a dicyclic
Lupinane structure/ring.
Lupinane Lupinine
+e.g. solanine, Protoveratrine A & B, Aconitine
+e.g. Sparteine
Conessine
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14. On the basis of nucleus/ Ring structure (9) , (10)
Alkaloids Ring Examples
Alkaloidal amino
group
The alkaloids in this group
do not contain
heterocyclic nitrogen
atoms. Some are
derivatives of
Phenylethylamine.
Phenylethylamine
Ephedrine
Purine
The alkaloids in this group
contain the Purine
nucleus which consists of
the six membered
Pyridine ring fused to the
five membered
Imidazole ring. . Purine
Caffeine
+e.g. Mescaline ,Colchicine
+e.g. Theobromine
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15. Basic ring structures
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16. Chemical Tests 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:-
Reagents ( Chemical composition) Clours of PPT
Mayer’s Reagents (Potassium mercuric iodide
solution)
Creamy ( Pale yellow) precipitate with True alkaloid
Exception: Alkaloids of the purine group and few others.
Wagner’s Reagent (solution of iodine in KI) Reddish brown ( or brown) precipitate with alkaloids
Hager's Reagents (a saturated solution of
picric acid)
Yellow (characteristic crystalline) precipitate (with many
alkaloids)
Dragendorff’s Reagents (Solution of
potassium bismuth iodide)
Reddish brown (Orange coloured) precipitate with
alkaloids
Tannic Acid Test (A freshly prepared aqueous
solution of tannic acid (5%, w/v))
Gives recipitate with most of the alkaloids which is soluble
in dilute acid or ammonia solution.
Ammonia Reineckate Test (A saturated aqueous solution
of ammonia retneckate slightly acidified with HCl)
Pink flocculent precipitate with most of the
alkaloids.
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17. Extraction of Alkaloid
Powdered material
Free alkaloid & other plant constituents
.
Moisture with aqueous alkali ( e.g. NaCO3, NaHCO3 or Lime- Ca(OH)2
Extract with organic solvent such as Benzene, Chloroform etc
Organic layer (alkaloid & other plant constituents) Aqueous layer (water soluble components)
Extract (shaken) with dilute ( aqueous) Acid
Aqueous layer (Containing alkaloidal salts) Organic layer (Other organic components e.g. impurities )
Precipitate of free alkaloid
(crude alkaloidal mixture)
Finally purification is accompanied by crystallization method
Add aqueous alkali
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18. 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.
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19. Pharmacological Action of Alkaloid
Activity Alkaloid
Analgesic & Narcotic Morphine and Codeine
CNS-stimulant Caffeine, Strychnine & Brucine
Cardiac depressant Qinidine
Mydriatic Atropine & Hematropine
Miotic Physostigmine, Pilocarpine
Hypertensive (BP) Ephedrine
Anti-Hypertensive Reserpine
Anti cancer Vincristine, Vinblastine
Myotic Pilocarpine
Antiamoebic & Emetic Emetine, Sanguinine
Anticholinergic Atropine, hyoscyamine
Antimalarial Quinine
Diuretic Theobromine, Theophylline
Antitussive Codeine, Noscapine
The alkaloids have a wide
range of pharmacological
actions:
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