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ALKALOIDS
Definition [adapted from Lewis’ Dictionary of Toxicology 1998] Alkaloid: Any of a large heterogeneous group of alkaline, bitter-tasting, biologically-active, usually water-insoluble, nitrogenous organic compounds produced mostly by dicotyledonous plants. Most are crystalline solids (a few liquids or gums) and are derivatives of heterocyclic and/or aromatic nitrogen ring compounds. Their trivial names usually end in –ine, e.g. atropine, strychnine.
Alkaloids are most commonly associated with the flowering plants, but there are other natural sources in cyanobacteria (q.v.), macrofungi (q.v.), amphibians (q.v.) and ants.