Alkaloids: An overview

Detail description of Alkaloids

1. Presented by
O. P. Verma
Associate Professor
M. Pharm, (Phd)


Dept. of Pharmacognosy

Goel Institute of Pharmacy and
Sciences, Lucknow

2. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
Alkaloids: An Overview
Metabolite: a metabolite is an intermediate or end product of metabolism.
Metabolites have various functions, including fuel, structure, signaling, stimulatory and
inhibitory effects on enzymes, catalytic activity (usually as a cofactor to an enzyme),
defense, and interactions with other organisms.

Difference between Primary Metabolites and Secondary Metabolites

Primary Metabolites Secondary Metabolites
The metabolites which are required
for the growth and maintenance of
cellular function are called primary
metabolites

The Secondary metabolites do not play a
role in growth, development, or
reproduction. However, they play a role in
ecological functions like defense
mechanisms, serve as antibiotics, and
produce pigments.
Primary metabolites are compounds
that are directly involved in the
growth and development of a plant
They also indirectly support the cell, in
sustaining their life for long duration.
Produced in large quantity and
extraction is easy
Produced in small quantity and extraction
is difficult
Primary metabolites are a part of the
basic molecular structure of an
organism.
Secondary metabolites are not a part of the
basic molecular structure of an organism.
Ex. vitamins, amino acids,
nucleosides, Alcohol and organic acids
Ex. alkaloids, Glycosides, resin, steroids,
antibiotics, pigments, toxins etc

3. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
ALKALOIDS
 Alkaloids are basic heterocyclic nitrogenous compounds of plant origin that are
physiologically active.
 Term alkaloids are derived from two Greek words ‘Alk- alkali’ and ‘Oids- like’ i.e.
alkali like substance.
 They are basic due to the presence of at least one nitrogen atom into the ring or
outside the ring.
 Alkaloids are a heterogenous group of natural substances widely distributed in the
plant kingdom and they give a different type of significant pharmacological action.
Distribution in Plant:
o All Parts e.g. Datura.
o Barks e.g. Cinchona
o Seeds e.g. Nux vomica
o Roots e.g. Aconite
o Fruits e.g. Black pepper
o Leaves e.g. Tobacco
o Latex e.g. Opium
Properties of alkaloids
With few exceptions, alkaloids are colorless, crystalline solid, and bitter with a sharp
melting point.
a. Physical Property
I- State:
o Most alkaloids are crystalline solids.
o Few alkaloids are amorphous solids e.g. emetine.
o Some are liquids that are either: Volatile e.g. nicotine and coniine, or Non-
volatile e.g. pilocarpine and hyoscine.
II- Colour:
o The majority of alkaloids are colorless but some are colored e.g.:
o Colchicine and berberine are yellow.
o Canadine is orange.
o Betanedine is red.

4. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
III- Solubility:
o Both alkaloidal bases and their salts are soluble in alcohol.
o Generally, the bases are soluble in organic solvents and insoluble in water
o Exceptions:
o Bases soluble in water: caffeine, ephedrine, codeine, colchicine, pilocarpine, and
quaternary ammonium bases.
o Bases insoluble or sparingly soluble in certain organic solvents: morphine in
ether, theobromine, and theophylline in benzene.
o Salts are usually soluble in water and, insoluble or sparingly soluble in
organic solvents.
Exceptions:
o Salts insoluble in water: quinine monosulphate.
o Salts soluble in organic solvents: lobeline and apoatropine hydrochlorides are
soluble in chloroform.
Chemical Properties:
➢ I- Nitrogen:
o Primary amines R-NH2 e.g. Norephedrine
o Secondary amines R2-NH e.g. Ephedrine
o Tertiary amines R3-N e.g. Atropine
o Quaternary ammonium salts R 4-N e.g d-Tubocurarine
➢ II- Basicity:
o R2-NH > R-NH2 > R3-N
o Saturated hexacyclic amines are more basic than aromatic amines.
➢ Stability:
o Effect of heat:
Alkaloids are decomposed by heat, except Strychnine and caffeine
(sublimable).
o Reaction with acids:
Salt formation
Dil acids hydrolyze Ester Alkaloids e.g. Atropine

5. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
General Classification
➢ True (Typical) Alkaloids
o They are derived from amino acids and have nitrogen in a heterocyclic ring.
o They are toxic.
e.g Atropine, Quinine, morphine, etc.

Atropine
➢ Proto-alkaloids/ Amino alkaloid
o They are simple amines derived from amino acids and do not have nitrogen in a
heterocyclic ring.
e.g
➢ Pseudo alkaloids or False alkaloids
o They are not derived from any amino acids but have nitrogen in a heterocyclic
ring.
o They do not show standard properties of alkaloids but they give a positive
response with their chemical tests.

e.g Caffeine

6. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
1. CHEMICAL OR STRUCTURAL CLASSIFICATION OF ALKALOIDS

7. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh

2. BIOSYNTHETIC CLASSIFICATION OF ALKALOIDS Biosynthetic classification:
Alkaloids Precursor Example
Indole alkaloids Trymptophan amino
acid.
vincristine, vinblastin
etc.
Piperidine alkaloids lysine amino acid(piperin, lobaline etc.
Pyrrolidine alkaloids ornithine amino acid. Nicotine etc.
Isoquinoline alkaloids tyrosine. morphine, codein,
emetine etc.
Imidazole alkaloids histidine pilocarpine,
isopilocarpine etc.
Amino/proto alkaloids phenylalanine amino
acid.
ephedrine etc.
Quinazolidine
alkaloids
Lupinine amino acid. vasaka etc.

8. OP Verma
Goel Institute of Pharmacy and Sciences, Lucknow, Uttar Pradesh
The liberation of the free bases:
Alkalis are used to liberate free bases. Alkalis must be strong enough to liberate
free bases. However, the choice of strong alkalis must be avoided in some cases:
 Ester Alkaloids e.g. Solanaceous Alkaloids
 Amide Alkaloids e.g. Colchicine
 Phenolic Alkaloids e.g. Morphine
 Lactone Alkaloids e.g. Pilocarpine
 Fatty Drugs due to saponification and emulsion formation

CHEMICAL TESTS FOR ALKALOIDS
1. Dragendorff’s test- (Potassium-bismuth-iodide solution)
Test: 1ml of drug+1ml of dragendorff’s reagent- A reddish-brown ppt. shows the
presence of alkaloids.
2. Mayer’s test- (Potassium mercuric iodide solution)
Test- 1ml of drug extract+1ml of Mayer's reagent- Whitish or cream-colored ppt
shows the presence of alkaloids.
3. Hager’s test-(Saturated aq. solution of picric acid)
Test- 1ml of drug extract + 3ml of Hager's reagent- Yellow-colored ppt shows the
presence of alkaloids.
4. Wagner’s test- (Iodine-potassium-iodide solution)
Test- Drug extract + Wagner's reagent- Brown or reddish-brown color shows the
presence of alkaloids.
5. Tannic acid test-
Test- Drug extract+5% tannic acid solution- Buff color ppt. shows the presence of
alkaloids.