Chemical structure of ephedrine, a phenethylamine alkaloid

Alkaloids are naturally occurring chemical compounds containing basic nitrogen atoms.^[1] The name derives from the word alkaline and was used to describe any nitrogen-containing base. 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. Some alkaloids have a bitter taste.

Caffeine

[edit] Alkaloid classifications

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.^[2][3] 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.^[3]

• Pyridine group: piperine, coniine, trigonelline, arecoline, arecaidine, guvacine, cytisine, lobeline, nicotine, anabasine, sparteine, pelletierine.
• Pyrrolidine 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
• Isoquinoline group: opium alkaloids (papaverine, narcotine, narceine), pancratistatin, sanguinarine, hydrastine, berberine, emetine, berbamine, oxyacanthine
• Phenanthrene 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
  • Vinca alkaloids: vinblastine, vincristine
  • Kratom (Mitragyna speciosa) alkaloids: mitragynine, 7-hydroxymitragynine
  • Tabernanthe iboga alkaloids: ibogaine, voacangine, coronaridine
  • Strychnos nux-vomica alkaloids: strychnine, brucine
• Purine group:
  • Xanthines: caffeine, theobromine, theophylline
• Terpenoid group:
  • Aconitum alkaloids: aconitine
  • Steroid alkaloids (containing a steroid skeleton in a nitrogen containing structure):
    • Solanum (e.g. potato and tomato) alkaloids (solanidine, solanine, chaconine)
    • Veratrum alkaloids (veratramine, cyclopamine, cycloposine, jervine, muldamine)^[4]
    • Fire Salamander alkaloids (samandarin)
    • Others: conessine
• Quaternary ammonium compounds: muscarine, choline, neurine
• Miscellaneous: capsaicin, cynarin, phytolaccine, phytolaccotoxin

[edit] Physicochemical properties

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.

[edit] See also

[edit] References

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