An
alkaloid is a nitrogen-containing naturally occurring compound, produced by a large variety of organisms, including
fungi,
plants,
animals, and
bacteria. Many alkaloids have
pharmacological effects on
humans and other
animals. The name derives from the word
alkaline; originally, the term was used to describe any nitrogen-containing
base. Alkaloids are part of the group of
natural products (also called
secondary metabolites) and are chemical derivatives of
amino acids or other nitrogen-containing compounds, such as
polyamines. Some alkaloids may have a
bitter taste. Produced in dedicated
biosynthetic pathways consisting of multiple
enzyme -catalysed steps, such as
prenylation,
methylation/
demethylation, and various
oxidation/
reduction reactions, alkaloids are found in plants (e.g.
potatoes and
tomatoes), animals (e.g.
shellfish) and many fungi. Many alkaloids can be purified from crude extracts by
acid-base extraction. While many alkaloids are
poisonous, some are used medicinally as
analgesics (pain relievers) or
anaesthetics, particularly
morphine and
codeine, and for other uses.
Alkaloids are usually classified by their common molecular precursors, based on the metabolic pathway used to construct the molecule. When not much was known about the biosynthesis of alkaloids, they were grouped under the names of known compounds, even some non-nitrogenous ones (since those molecules' structures appear in the finished product; the opium alkaloids are sometimes called "phenanthrenes", for example), or by the plants or animals they were isolated from. When more is learned about a certain alkaloid, the grouping is changed to reflect the new knowledge, usually taking the name of a biologically-important amine that stands out in the synthesis process.
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