2. HISTORY OF ALKALOIDS:
The term ‘ alkaloid ’ was coined by MEISSNER,
a German pharmacist, in 1819.
The French chemist, Derosne in 1803, isolated
narcotine . In the same year , morphine from
opium was isolated by Serturner .
Pelletier and Caventon isolated emetine in
1817 and colchicine in 1819.
3. From the beginning of 19th century till to date,
it has to proved to be a perpetual work to
discover new alkaloids from plants and
As per a Russian review in 1973, the numbe of
known alkaloids had reached upto 4959,
amongst which, the structures of 3293
alkaloids were elucidated.
5. What is alkaloid ?
The term “alkaloid” (alkali-like) is commonly
used to designate basic heterocyclic
nitrogenous compounds of plant origin that
are physiologically active.
They resemble some of the characters of
naturally occuring complex amines.
6. It posses specific physiological actions on
human or animal body ,when used in small
STRUCUTE OF ALKALOID
8. The term alkaloid also covers proto alkaloid ,
pseudoalkaloids and True alkaloids.
The true alkaloids are toxic in nature
and contain heterocyclic nitrogen which is
derived from amino acids and always basic in
nature. True alkaloids are normally present in
plants as salts of organic acids.
The ‘protoalkaloids’ or ‘amino alkaloids’
are simple amines in which the nitrogen is not
in a heterocyclic ring. They are basic in nature
and prepared in plants from amino acids
It includes mainly steroidal and
terpenoid alkaloids and purines.They are not
derived from amino acids.
10. OCCURENCE OF ALKALOIDS:
Alkaloids are occurs mostly in angiosperms and
rarely in gymnosperms.
But their presence is also detected in micro
organisms, marine organisms, insects,
animals and some of the lower plants.
In the lower plants, although the alkaloids are
found in less number, some important sources
11. are ergot fungus giving peptide alkaloids ,
ergometrine, ergotamine etc., and also
gymnosperms like ephedra alkaloids.
Out of 60 different orders in higher plants, 34
orders contain alkaloids.
Families with alkaloidal content are
Rubiaceae and Solanaceae
In most of the plants alkaloids are highly localized
and concentrated in certain morphological parts
• All Parts e.g. Datura.
• Barks e.g. Cinchona,kurchi
• Seeds e.g. Nux vomica , areca, physostigma
• Roots e.g. Aconite , rauwolfia
• Fruits e.g. Black pepper, conicum
• Leaves e.g. Tobacco, coca, lobelia
• Latex e.g. Opium
14. PROPERTIES OF ALKALOIDS:
• Mostly all alkaloids are colourless, crystalline
• Sharp melting point
• Bitter taste
• Some alkaloids are coloured in nature,
e.g. Berberine is yellow
15. • Soluble in organic non-polar, immiscible
• The alkaloids containing quaternary bases are
only water soluble.
• Some of the pseudoalkaloids and
protoalkaloids shows higher solubility in
16. • Some alkaloids are liquid because of lacking of
oxygen in their molecules. (e.g coniine,
• Alkaloids are decomposed by heat, except
Strychnine and caffeine.
• Give a precipitate with heavy metal iodides.
The various methods proposed for
classification of alkaloids are explained as
1. Pharmacological classification
2. Taxonomic classification
3. Biosynthetic classification
4. Chemical classification
18. PHARMACOLOGICAL CLASSIFICATION:
Depending on the physiological response, the
alkaloids are classified under various
pharmacological categories, like central
nervous system stimulants or depressants,
analgesics , purgatives etc.
Some of the examples are explained as
19. 1. Narcotic analgesic e.g.Morphine
2. Antimalarial e.g. Quinine
3. Reflux excitability e.g.Strychnine
4. Respiratory stimulant e.g.Lobeline
5. Neuralgia e.g. Aconitine
6. Oxytoxic e.g. Erogotometrine
7. Bronchodilator e.g. Ephedrine, vasicine
8. Anticholinergic e.g. Atropine
20. 9. CNS stimulant e.g. Caffeine
10.Antitussive e.g. Codeine
12.Antihypertensive e.g. Reserpine
13.Anticancer e.g. Vincristine
14.Antiglucoma e.g. Pilocarpine
21. TAXONOMIC CLASSIFICATION:
This method classifies vast number of alkaloids
based on their distribution in various plant
families, like solanaceous or papillionaceous
From this classification, the chemotaxonomic
classification has been further derived.
22. BIOSYNTHETIC CLASSIFICATION:
This method give significance to the precursor
from which the alkaloids are biosynthesized in
The alkaloidal drugs are categorised on the
fact whether they are derived from amino acid
precursor as ornithine, lysine, tyrosine,
tryptophan, phenylalanine etc.
25. CHEMICAL CLASSIFICATION:
• This is the most accepted way of classification
of alkaloids. The main criterion for chemical
classification is the type of fundamental
(normal heterocyclic) ring structure present in
• The alkaloidal drug care broadly categorised
into 2 divisions.
26. (a) Heterocyclic alkaloids (True alkaloids) are
divided into 12 groups according to nature of
their heterocyclic ring.
(b)Non- heterocyclic alkaloids or protoalkaloids
or Biological amines or pseudoalkaloids.
The following chart indicates types of alkaloids
and their occurence in various plants
alongwith basic chemical ring.
27. A) True alkaloids
Sr. no. Type Structure Examples
1. Pyrrole and
e.g. Hygrine, coca species
2. Pyiridine and
e.g. Arecoline, anabasine, lobeline,
e.g. Echimidine, senecionine,
e.g. Atropine, hyoscine, hyoscyamine,
e.g. Quinine, quinidine, cinchonine,
e.g.Morphine, codeine, emetine,
cephaline, narcotine, narceine, d-
28. 7 Indole
e.g. Erotamine, ergotametriene,
reserpine, vincristine, vinblastine,
8 Imidazole N
e.g. Pilocrpine, isopilocarpine, pilosine
e.g. Cystisine, laburinine
29. B) PROTOALKALOID
e.g. Caffeine, thophylline, theobromine
2. Steroidal e.g. Solanidine, conessine,
3. Diterpene C20H32 e.g. Aconitine, aconine, hypoaconine
30. ISOLATION OF ALKALOID:
1. Plant material is dried at a temperature not
exceeding 60 ˚c and finely powdered.
2. Macerate the powdered material with
sufficient quantity of ethanol and set aside
over night. Most alkaloids and their salts
being alcohol soluble will get dissolved in the
3. Filter and concentrate the extract to ¼ the
initial volume. complete the evaporation of
the remaining solvent at a temperature not
31. 4. Treat the residue with dil.sulphuric acid and
filter to remove resins, fatty matter and other
5. Basify the solution by the addition of alkali
such as ammonia as it effectively precipitates
most alkaloids and because of its volatility.
6. Extract this solution with succesive portion of
chloroform or till complete extraction of all
the alkaloids is effected.
32. 7. Concentrate the pooled organic layer to yield
a crude mixture of alkaloids of the plant
8. Dissolve the above residue in dil.sulphuric
acid and filter if necessary.
9. Basify the solution with ammonia and
successively extract with chloroform.
33. 10. Run the pooled chloroform layers through a
bed of anhydrous sodium sulphate and
evaporate to dryness .Note the weight of the
mixture of total alkaloids.
34. QUALITATIVE CHEMICAL TEST:
(+) Reddish brown precipitate
Reagent used: Wagner’s Reagent
[Solution of iodine in potassium iodide]
(+) Cream color precipitates
Reagent used: Mayer’s Reagent
[Potassium mercuric iodide solution]
35. Dragendorff’s test
(+) Orange precipitate
Reagent used: Dragendorff’s reagent
[Potassium bismuth iodide solution]
(+) Yellow color precipitate
Reagent used: Hager's reagent
[saturated solution of Picric acid]