From Wikipedia, the free encyclopedia
Chemical structure of ephedrine
, a phenethylamine alkaloid
Alkaloids are naturally occurring chemical
compounds containing basic nitrogen atoms. The
name derives from the word alkaline and is used to describe any
nitrogen-containing base and organic compounds with one or more of
the following features: a heterocyclic compound containing
nitrogen, with an alkaline pH and a
marked physiological action on animal physiology. However, There
are exceptions to each of these criteria. Alkaloids are produced by
a large variety of organisms, including bacteria, fungi, plants, and animals and are part of the group of natural products (also called secondary
metabolites). Many alkaloids can be purified from crude
extracts by acid-base extraction. Many
alkaloids are toxic to
other organisms. They often have pharmacological effects and are used as medications, as recreational drugs, or in entheogenic rituals. Examples are the local
anesthetic and stimulant cocaine, the stimulant caffeine, nicotine, the analgesic morphine, or the antimalarial drug quinine. Most alkaloids have a bitter taste.
The classification of the alkaloids is complex and may be guided
by a set of rules that take into account the structure
and other chemical features of the alkaloid molecule, its
biological origin, as well as the biogenetic origin where known.
For example, where the biosynthesis pathway of an alkaloid is
unknown, it may be grouped based on structural similarities with
known compounds, including non-nitrogenous compounds, or by the
organism(s) from which the alkaloid was isolated.
- Pyridine group: piperine, coniine, trigonelline, arecoline, arecaidine, guvacine, cytisine, lobeline, nicotine, anabasine, sparteine, pelletierine.
group: hygrine, cuscohygrine, nicotine
- Tropane group: atropine, cocaine, ecgonine, scopolamine, catuabine
- Indolizidine group: senecionine, swainsonine
- Quinoline group: quinine, quinidine, dihydroquinine, dihydroquinidine, strychnine, brucine, veratrine, cevadine
group: opium alkaloids (papaverine, narcotine, narceine), pancratistatin,
sanguinarine, hydrastine, berberine, emetine, berbamine, oxyacanthine
alkaloids: opium alkaloids (morphine, codeine, thebaine, oripavine)
- Phenethylamine group: mescaline, ephedrine, dopamine
- Indole group:
- Tryptamines: serotonin, DMT, 5-MeO-DMT, bufotenine, psilocybin
- Ergolines (the ergot alkaloids): ergine, ergotamine, lysergic acid
- Beta-carbolines: harmine, harmaline, tetrahydroharmine
- Yohimbans: reserpine, yohimbine
alkaloids: vinblastine, vincristine
- Kratom (Mitragyna
speciosa) alkaloids: mitragynine, 7-hydroxymitragynine
- Tabernanthe iboga alkaloids: ibogaine, voacangine,
nux-vomica alkaloids: strychnine, brucine
- Purine group:
- Terpenoid group:
- Quaternary ammonium
compounds: muscarine, choline, neurine
- Miscellaneous: capsaicin, cynarin, phytolaccine,
Low-molecular weight alkaloids without hydrogen bond donors such as hydroxy groups are often liquid at room
temperature, examples are nicotine, sparteine, coniine, and phenethylamine.
The basicity of alkaloids depends on the lone pairs of electrons on their nitrogen atoms. As organic
bases, alkaloids form salts with mineral acids such as hydrochloric
acid and sulfuric acid and organic acids such as tartaric acid or maleic acid. These
salts are usually more water-soluble than their free base form.
With the exception of caffeine, alkaloids are one of several classes
of compound which are generally precipitated from aqueous solutions
by tannins, a fact which is important in herbalism.