Originally, any one of hundreds of plant products distinguished by alkaline (basic) reactions, but now restricted to heterocyclic nitrogen-containing and often complex structures possessing pharmacological activity; their trivial names usually end in -ine (e.g., morphine, atropine, colchicine). Alkaloids are synthesized by plants and are found in the leaf, bark, seed, or other parts, usually constituting the active principle of the crude drug; they are a loosely defined group, but may be classified according to the chemical structure of their main nucleus. For medicinal purposes, due to improved water solubility, the salts of alkaloids are usually used. See also individual alkaloid or alkaloid class. Syn: vegetable base.
ergot alkaloids
fixed alkaloid
Vinca alkaloids