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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 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.

Caffeine, a Purine alkaloid
Chemical structure of Vinblastine, a Chemotheraputic alkaloid isolated from the Madagascar periwinkle

Contents

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]

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.

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.

See also

References

  1. ^ International Union of Pure and Applied Chemistry (1995). "alkaloids". Compendium of Chemical Terminology Internet edition.
  2. ^ Rogers MF, Wink M. (1998). Alkaloids: biochemistry, ecology, and medicinal applications. Plenum Press. pp. 2–3. ISBN 0-306-45465-3.  
  3. ^ a b Hesse M. (2005). Alkaloids: nature's curse or blessing?. Plenum Press. pp. 11–114. ISBN 0-306-45465-3.  
  4. ^ http://www.ansci.cornell.edu/plants/toxicagents/steroid.html,

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