Alkaloids are nitrogen-containing organic compounds found in plants that have strong physiological effects. True alkaloids are derived from amino acids and have nitrogen in a heterocyclic ring, while other classes of alkaloids like pseudoalkaloids and protoalkaloids vary in their origin and structure. Alkaloids serve functions like protecting plants from herbivores and can have pharmacological actions like analgesic, stimulant, or respiratory effects when consumed. They are classified based on their chemical structure and pharmacological properties.

1. Alkaloids
Prepared by,
Ms. M. S. Divya Sree,
Assistant Professor,
Department of Pharmacognosy,
Sree Vidyanikethan College of Pharmacy,
Tirupati.

2. Definition
 The term “alkaloid” (alkali-like) is
commonly used to designate basic
heterocyclic nitrogenous compounds of
plant origin that are physiologically
active.

3. Deviation from Definition:
 Basicity: Some alkaloids are not basic e.g. Colchicine,
Piperine, Quaternary alkaloids.
 Nitrogen: The nitrogen in some alkaloids is not in a
heterocyclic ring e.g. Ephedrine, Colchicine, Mescaline.
 Plant Origin: Some alkaloids are derived from Bacteria,
Fungi, Insects, Frogs, Animals.
 Biosynthesis: Some alkaloids are not derived from amino
acids e.g purine, steroidal alkaloid.

5. Classification
 True (Typical) alkaloids that are derived from amino acids
and have nitrogen in a heterocyclic ring. e.g Atropine
 Proto alkaloids that are derived from amino acids and do not
have nitrogen in a heterocyclic ring. e.g Ephedrine
 Pseudo alkaloids that are not derived from amino acids but
have nitrogen in a heterocyclic ring. e.g Caffeine
 False alkaloids are non alkaloids give false positive reaction
with alkaloidal reagents.

6. New Definition
 Alkaloids are cyclic organic compounds
containing nitrogen in a negative state of
oxidation with limited distribution among
living organisms.

7. Distribution and occurrence
 Rare in lower plants.
 Dicots are more rich in alkaloids than
Monocots.
 Families rich in Alkaloids: Apocynaceae,
Rubiaceae, Solanaceae and Papaveracea.
 Families free from Alkaloids: Rosaceae,
Labiatae

8. Distribution in Plants
 All Parts e.g. Datura.
 Barks e.g. Cinchona
 Seeds e.g. Nux vomica
 Roots e.g. Aconite
 Fruits e.g. Black pepper
 Leaves e.g. Tobacco
 Latex e.g. Opium

9. General properties
 Naturally occurring compounds in plants (mainly)
 Nitrogen containing (heterocyclic) basic compounds
 With strong physiological effect
 Occurring in the form of salt with organic acids
 Common precursors

10. Forms of Alkaloids
 Free bases
 Salts with Organic acids e.g. Oxalic, acetic acids
 Salts with inorganic acids e.g. HCl, H2SO4.
 Salts with special acids:
e.g. Meconic acid in Opium
Quinic acid in Cinchona
 Glycosidal form e.g. Solanine in Solanum.

11. Properties
 Insoluble or sparingly soluble in water, but the salts
formed on reaction with acids are usually freely
soluble.
 Most are crystalline solids (although a few are
amorphous).
 Free alkaloids are usually soluble in ether, chloroform,
or other relatively non-polar immiscible solvents.

12.  The degree of basicity varies greatly, depending on
the structure of the molecule and the presence and
location of other functional groups.
 Have high melting points
 Some alkaloids are liquid because of lacking of
oxygen in their molecules. (e.g coniine, nicotine,
spartenine)

13. Function in Plants
 Poisonous agents which protect plants against
insects and herbivores
 They are in certain cases, the final products
of detoxification (waste products).
 Source of nitrogen in case of nitrogen
deficiency.

14.  They sometimes act as growth regulators
in certain metabolic systems.
 They may be utilized as a source of energy
in case of deficiency in carbon dioxide
assimilation.

15. Pharmacological actions
 Analgesic (morphine, codeine)
 Narcotics (strychnine, brucine which are central
stimulant)
 Mydriatics (atropine)
 Miotics (physostigmine, pilocarpine)
 Ephedrine (rises in blood pressure)
 Reserpine (produce fall in excessive hypertension)

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

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

18. 5) Tannic acid test
(+) buff color precipitate
Reagent used: 10% Tannic acid solution
6) Valser’s Test
(+) white precipitate
Reagent used: Valser’s reagent (Mercuric Iodide TS)

19. Classification
(Chemical Classification)
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. Pyrrolizdine
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

20. 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 Piporphine
(reduced
isoquinoline
napthalene)
N
e.g. Boldine

21. 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

22. Pharmacological Classification
1. Narcotic analgesic e.g.Morphine
2. Antimalerial e.g. Quinine
3. Reflux excitability e.g.Strychnine
4. Respiratory stimulant e.g.Lobeline
5. Neuralgia e.g. Aconitine
6. Oxytocic e.g. Erogotometrine
7. Bronchodilator e.g. Ephedrine, vasicine

23. Pharmacological classification
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