Alkaloids

ALKALOIDS
BY
NIVETHA.B
M.PHARM

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.

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
animals.
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.

At present, the number of alkaloids discovered
has exceeded 6000.

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.

It posses specific physiological actions on
human or animal body ,when used in small
quantities.
STRUCUTE OF ALKALOID

The term alkaloid also covers proto alkaloid ,
pseudoalkaloids and True alkaloids.
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.

PROTOALKAOIDS:
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
PSEUDOALKALOIDS:
It includes mainly steroidal and
terpenoid alkaloids and purines.They are not
derived from amino acids.

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

are ergot fungus giving peptide alkaloids ,
ergometrine, ergotamine etc., and also
gymnosperms like ephedra alkaloids.

DISTRIBUTION:
Out of 60 different orders in higher plants, 34
orders contain alkaloids.
Families with alkaloidal content are
Apocynaceae,Berberidaceae,Euphorbiaceae,Legu
minosae,Papaveraceae,Ranunculaceae,Rutaceae,
Rubiaceae and Solanaceae
In most of the plants alkaloids are highly localized
and concentrated in certain morphological parts
only.

Examples:
• 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

PROPERTIES OF ALKALOIDS:
• Mostly all alkaloids are colourless, crystalline
solids
• Sharp melting point
• Bitter taste
• Some alkaloids are coloured in nature,
e.g. Berberine is yellow

• Soluble in organic non-polar, immiscible
solvents.
• The alkaloids containing quaternary bases are
only water soluble.
• Some of the pseudoalkaloids and
protoalkaloids shows higher solubility in
water.

• Some alkaloids are liquid because of lacking of
oxygen in their molecules. (e.g coniine,
nicotine, spartenine)
• Alkaloids are decomposed by heat, except
Strychnine and caffeine.
• Give a precipitate with heavy metal iodides.

CLASSIFICATION:
The various methods proposed for
classification of alkaloids are explained as
follows,
1. Pharmacological classification
2. Taxonomic classification
3. Biosynthetic classification
4. Chemical classification

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
follows,

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

9. CNS stimulant e.g. Caffeine
10.Antitussive e.g. Codeine
11.Antiarrythmic e.g.Quinidine
12.Antihypertensive e.g. Reserpine
13.Anticancer e.g. Vincristine
14.Antiglucoma e.g. Pilocarpine

TAXONOMIC CLASSIFICATION:
This method classifies vast number of alkaloids
based on their distribution in various plant
families, like solanaceous or papillionaceous
alkaloids.
From this classification, the chemotaxonomic
classification has been further derived.

BIOSYNTHETIC CLASSIFICATION:
This method give significance to the precursor
from which the alkaloids are biosynthesized in
plants.
The alkaloidal drugs are categorised on the
fact whether they are derived from amino acid
precursor as ornithine, lysine, tyrosine,
tryptophan, phenylalanine etc.

1. Ornithine derived alkaloids
e.g. Pyrrolidine alkaloid-Nicotine
Tropane alkaloid - Atropine, hyosyamine,
coacaine
2. Lysine derived alkaloids
e.g. Piperidine and pyridine alkaloid - conine,
lobaline, arecoline
Quinazolidine alkaloid- lupinine
3. Tyrosine derived alkaloids
e.g. Isoquinoline alkaloid - Morphine, codeine,
emetine, cephaline, berberine,d- tubocurine
Amino alkaloid- colchicine

4. Tryptophan derived alkaloids
e.g. Indole alkaloid- ergot alkaloid, vincristine,
vinblastine, reserpine, strychnine,
physostigmine, strychinine, brucine
Quinoline alkaloid -cinchonine, quinine.
5. Histidine derived alkaloids
e.g. Imidazole alkaloid - Pilocrpine
6. Phenylalanine derived alkaloids
e.g. Amino alkaloid- Ephedrine

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
alkaloid.
• The alkaloidal drug care broadly categorised
into 2 divisions.

(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.

A) True alkaloids
Sr. no. Type Structure Examples
1. Pyrrole and
pyrrolidine
N
H
N
H
e.g. Hygrine, coca species
2. Pyiridine and
piperidine
N N
H
e.g. Arecoline, anabasine, lobeline,
conine, trigonelline
3. Pyrrolizidine
N
e.g. Echimidine, senecionine,
seneciphylline
4. Tropane
N
e.g. Atropine, hyoscine, hyoscyamine,
cocaine, pseudopelletirine
5. Quinoline
N
e.g. Quinine, quinidine, cinchonine,
cupreine, camptothecine
6. Isoquinoline
N
e.g.Morphine, codeine, emetine,
cephaline, narcotine, narceine, d-
tubocurarine

7 Indole
N
H
e.g. Erotamine, ergotametriene,
reserpine, vincristine, vinblastine,
strychnine, brucine
8 Imidazole N
N
H
e.g. Pilocrpine, isopilocarpine, pilosine
9 Norlupinane
N
e.g. Cystisine, laburinine
10 Aporphine
(reduced
isoquinoline
napthalene)
N
e.g. Boldine

B) PROTOALKALOID
1. Alkyalamine
HO
NH
Ephedrine, Pseudoephedrine
C) PSEUDOALKALOID
1. Purine
N
NN
HN
e.g. Caffeine, thophylline, theobromine
2. Steroidal e.g. Solanidine, conessine,
protoveratrine
3. Diterpene C20H32 e.g. Aconitine, aconine, hypoaconine

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
solution.
3. Filter and concentrate the extract to ¼ the
initial volume. complete the evaporation of
the remaining solvent at a temperature not
exceeding 50˚c.

4. Treat the residue with dil.sulphuric acid and
filter to remove resins, fatty matter and other
unwanted substances.
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.

7. Concentrate the pooled organic layer to yield
a crude mixture of alkaloids of the plant
material.
8. Dissolve the above residue in dil.sulphuric
acid and filter if necessary.
9. Basify the solution with ammonia and
successively extract with chloroform.

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.

QUALITATIVE CHEMICAL TEST:
Wagner’s Test
(+) Reddish brown precipitate
Reagent used: Wagner’s Reagent
[Solution of iodine in potassium iodide]
Mayer’s Test
(+) Cream color precipitates
Reagent used: Mayer’s Reagent
[Potassium mercuric iodide solution]

Dragendorff’s test
(+) Orange precipitate
Reagent used: Dragendorff’s reagent
[Potassium bismuth iodide solution]
Hager's test
(+) Yellow color precipitate
Reagent used: Hager's reagent
[saturated solution of Picric acid]

Tannic acid test
(+)buff color precipitate
Reagent used: 10% Tannic acid solution

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