An alkaloid is, strictly speaking, an amine that is produced by a plant. However, the term has been extended to amines produced by animals and fungi as well. The name derives from the word alkaline; originally, the term was used to describe any nitrogen-containing base.
Alkaloids are usually derivatives of amino acids, and many have a bitter taste. They are found as secondary metabolites in plants (such as potatoes and tomatoes), animals (such as shellfish), and fungi. In many cases, they can be purified from crude extracts by acid-base extraction.
Various alkaloids have pharmacological effects on humans and animals. Many are poisonous, but some are used medicinally as analgesics (pain relievers) or anesthetics, particularly morphine and codeine. Some, such as vinblastine, are used to treat certain types of cancer.
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.
|Major families of biochemicals|
|Peptides | Amino acids | Nucleic acids | Carbohydrates | Nucleotide sugars | Lipids | Terpenes | Carotenoids | Tetrapyrroles | Enzyme cofactors | Steroids | Flavonoids | Alkaloids | Polyketides | Glycosides|
|Analogues of nucleic acids:||Types of Alkaloids||Analogues of nucleic acids:|
|Indole group:||5-MeO-DMT | Dimethyltryptamine | Harmala alkaloids | Psilocin | Psilocybin | Reserpine | Serotonin | Tryptamine | Yohimbine|
|Phenethylamine group:||Amphetamine | Cathinone | Ephedrine | Mescaline | Methamphetamine | Phenethylamine | Tyramine|
|Purine group:||Caffeine | Theobromine | Theophylline|
|Isoquinoline group:||Codeine | Morphine|
|Tropane group:||Atropine | Cocaine | Hyoscyamine | Scopolamine|
|Terpenoid group:||Aconitine | Solanine|
|Betaines:||Choline | Muscarine|
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