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). A.'s 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 a.'s are usually used. See also individual a. or a. class.vegetable base;
ergot a.'s (er´got) any of a large number of a.'s obtained from the ergot fungus Claviceps purpurea or semisynthetically derived; examples include ergotamine, ergonovine, dihydroergotamine, lysergic acid diethylamide (LSD), methysergide.
fixed a. a nonvolatile a.
Vinca a.'s a.'s such as vincristine and vinblastine (antitumor agents) extracted from the periwinkle plant.Catharanthus alkaloids;
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