An alkaloid is any of a group of basic nitrogen-containing organic compounds (mostly heterocyclic) derived from plants and having diverse pharmacological properties. Alkaloids include morphine, cocaine, atropine, quinine, codeine, nicotine, and caffeine, some of which are used in medicine as analgesics, tranquilizers, anesthetics, and cardiac and respiratory stimulants.
Many alkaloids consist of a core structure that is common to many compounds. Often, this core has a nitrogen-containing ring. Because many different compounds can be made from the same core structure (say, a 5-membered nitrogen-containing ring), methods for making these core structures can find a lot of use in pharmaceutical research.
Some alkaloids, such as strychnine, atropine, and coniine (from hemlock) are extremely poisonous. Colchicine inhibits cell division. Others such as morphine, nicotine, and cocaine, are highly addictive, and some, such as mescaline, are hallucinogenic drugs.
Although alkaloids may be found in any part of a plant, they are usually contained in the seeds, seed capsules, bark, or roots. One plant, the opium poppy, contains about 30 alkaloids. Alkaloids are extracted from plants and separated by chromatography; synthetic alkaloids are seldom economically competitive.