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

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

New Definition:

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


 The term alkaloid was coined by Meissner, A German Pharmacist, in 1819.
 The mankind has been using alkaloid for various purposes like poisons, medicines, poultices, teas and etc.
 The French chemist, Derosne in 1803, isolated Narcotine.
 A significant contribution to the chemistry of alkaloids in the early years of its development was made by the French researchers Pierre Joseph Pelletier and Joseph Bienaimé Caventou, who discovered quinine (1820) and strychnine (1818).
 Several other alkaloids were discovered around that time, including xanthine (1817), atropine (1819), caffeine (1820), coniine (1827), nicotine (1828), and cocaine (1860).


Trivial names should end by “ine”. These names may refer to:

From plant generic name (Atropine)
From specific plant species (Cocaine)
From the common name of Drug (Ergotamine)
From physiological activity (emetine)
From the name of discoverer (Pelletierine)
From the prominent Physical character (Hygrine)

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

Distribution in Plant:

All Parts e.g. Datura.
Barks e.g. Cinchona
Seeds e.g. Nux vomica
Fruits e.g. Black pepper
Latex e.g. Opium
Leaves e.g. Tobacco

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.

Function in Plants

• They may act as protective against insects and herbivores due to their bitterness and toxicity.
• They are, in certain cases, the final products of detoxification (waste products).
• Source of nitrogen in case of nitrogen deficiency.
• 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.


High Biological Activity
Produce Vary Degrees Of Physiological and Psychological Responses – Largely by interfering with Neurotransmitter
In large doses- highly toxic – fatal
In small doses – many have therapeutic value
Muscle relaxant, Pain killers, tranquilizers, Mind altering drugs, Chemotherapy

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