[[Image:Ephedrine.png|thumb|Chemical structure of [[ephedrine]], a phenethylamine alkaloid]]

An '''alkaloid''' is, strictly speaking, a naturally occurring [[amine]] produced by a [[plant]], but amines produced by [[animal]]s and [[fungus|fungi]] are also called alkaloids<ref>{{cite book | last = Carey | first = Francis A. | title = Organic Chemistry | origyear = 1987 | edition = 6th ed. | year = 2006 | publisher = McGraw Hill | location = New York | id = ISBN 0-07-282837-4 | pages = 954 | quote = (Strictly speaking, these compounds are not classified as alkaloids because they are not isolated from plants.)}}</ref>. Many alkaloids have [[pharmacology|pharmacological]] effects on [[human]]s and other [[animal]]s. The name derives from the word [[alkaline]]; originally, the term was used to describe any nitrogen-containing [[base (chemistry)|base]]. Alkaloids are usually derivatives of [[amino acids]], and many have a [[Bitter (taste)#Bitterness|bitter taste]]. They are found as [[secondary metabolite]]s in plants (e.g. [[potato]]es and [[tomato]]es), animals (e.g. [[shellfish]]) and fungi. Many alkaloids can be purified from crude extracts by [[acid-base extraction]].
While many alkaloids are [[poison]]ous, some are used medicinally as [[analgesic]]s (pain relievers) or [[anaesthetic]]s, particularly [[morphine]] and [[codeine]], and for other uses.

== Alkaloid classifications ==
Alkaloids are usually classified by their common molecular feat, 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.
* [[Pyridine]] group: [[piperine]], [[coniine]], [[trigonelline]], [[arecaidine]], [[guvacine]], [[pilocarpine]], [[cytisine]], [[nicotine]], [[sparteine]], [[pelletierine]].
* [[Pyrrolidine]] group: [[hygrine]], [[cuscohygrine]], [[nicotine]]
* [[Tropane]] group: [[atropine]], [[cocaine]], [[ecgonine]], [[scopolamine]], [[catuabine]]
* [[Quinoline]] group: [[quinine]], [[quinidine]], [[dihydroquinine]], [[dihydroquinidine]], [[strychnine]], [[brucine]], [[veratrine]], [[cevadine]]
* [[Isoquinoline]] group: The [[opium]] alkaloids ([[morphine]], [[codeine]], [[thebaine]], [[Isopapa-dimethoxy-aniline]], [[papaverine]], [[narcotine]], [[sanguinarine]], [[narceine]], [[hydrastine]], [[berberine]]), [[emetine]], berbamine, oxyacanthine
* [[Phenethylamine]] group: [[mescaline]], [[ephedrine]], [[dopamine]], [[amphetamine]]
* [[Indole]] group:
** [[Tryptamine]]s: [[dimethyltryptamine|DMT]], [[N-methyltryptamine]], [[psilocybin]], [[serotonin]]
** [[Ergoline]]s: the [[ergot]] alkaloids ([[ergine]], [[ergotamine]], [[lysergic acid]], etc.)
** [[Beta-carboline]]s: [[harmine]], [[Harmala alkaloid|harmaline]], [[yohimbine]], [[reserpine]]
** [[Rauwolfia]] alkaloids: [[Reserpine]]
* [[Purine]] group:
** [[Xanthine]]s: [[caffeine]], [[theobromine]], [[theophylline]]
* [[Terpenoid]] group:
** [[Aconite]] alkaloids: [[aconitine]]
** [[Steroid]]s: [[solanine]], [[samandari]]s ([[ammonium|quaternary ammonium compound]]s): [[muscarine]], [[choline]], [[neurine]]
* [[Vinca alkaloids]]: [[vinblastine]], [[vincristine]]. They are antineoplastic and binds free tubulin dimers thereby disrupting balance between microtuble polymerization and delpolymerization resulting in arrest of cells in metaphase.
* Miscellaneous: [[capsaicin]], cynarin, phytolaccine, phytolaccotoxin

== Physicochemical Properties of Alkaloids ==
*colourless,crystalline,non-volatile solids that are insoluble in water but soluble in organic solvents such as ethanol,ether,chloroform,etc.
* Molecular weight 100-900
* Those without oxygen atoms in the structure are usually liquid at ordinary temperature (e.g. nicotine, sparteine, coniine)
* Those with oxygen atoms are crystalline (e.g. berberine -> yellow)
* Most are optically active (usually [[Levorotation|laevorotatory]]), but not those from the purine group
* Basicity depends on the availability of lone pairs of electrons on the N atom & the type of heterocycle and substituents.
* Ability to form salts with mineral acids (e.g. with HCl, H₂SO₄, HNO₃) or organic acids (e.g. tartrates, sulfamates, maleates)

{{IPA|}}

== References ==
{{Commons|Alkaloid}}

<!-- See [[Wikipedia:Footnotes]] for an explanation of <ref> tags. -->
<div class="references-small"><references /></div>

{{alkaloids}}

[[Category:Natural products]]
[[Category:Alkaloids| ]]

[[ar:قلويد]]
[[bn:উপক্ষার]]
[[bg:Алкалоид]]
[[ca:Alcaloide]]
[[cs:Alkaloidy]]
[[da:Alkaloid]]
[[de:Alkaloide]]
[[et:Alkaloidid]]
[[es:Alcaloide]]
[[eo:Alkaloido]]
[[fr:Alcaloïde]]
[[it:Alcaloidi]]
[[he:אלקלואיד]]
[[lv:Alkaloīdi]]
[[lt:Alkaloidas]]
[[nl:Alkaloïde]]
[[ja:アルカロイド]]
[[no:Alkaloid]]
[[nn:Alkaloid]]
[[pl:Alkaloidy]]
[[pt:Alcalóide]]
[[ro:Alcaloid]]
[[ru:Алкалоид]]
[[sk:Alkaloid]]
[[sl:Alkaloid]]
[[sr:Алкалоид]]
[[sh:Alkaloid]]
[[fi:Alkaloidi]]
[[sv:Alkaloid]]
[[vi:Ancaloit]]
[[tr:Alkaloid]]
[[uk:Алкалоїди]]
[[zh:生物鹼]]