alkaloid

[ALKAL(I) + -OID.]

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A cyclic organic compound that contains nitrogen in a negative oxidation state and is of limited distribution among living organisms. Over 10,000 alkaloids of many different structural types are known; and no other class of natural products possesses such an enormous variety of structures. Therefore, alkaloids are difficult to differentiate from other types of organic nitrogen-containing compounds.

Simple low-molecular-weight derivatives of ammonia, as well as polyamines and acyclic amides, are not considered alkaloids because they lack a cyclic structure in some part of the molecule. Amines, amine oxides, amides, and quaternary ammonium salts are included in the alkaloid group because their nitrogen is in a negative oxidation state (the oxidation state designates the positive or negative character of atoms in a molecule). Nitro and nitroso compounds are excluded as alkaloids. The almost-ubiquitous nitrogenous compounds, such as amino acids, amino sugars, peptides, proteins, nucleic acids, nucleotides, prophyrins, and vitamins, are not alkaloids. However, compounds that are exceptions to the classical-type definition (that is, a compound containing nitrogen, usually a cyclic amine, and occurring as a secondary metabolite), such as neutral alkaloids (colchicine, piperine), the β-phenyl-ethylanines, and the purine bases (caffeine, theophylline, theobromine), are accepted as alkaloids.

Alkaloids often occur as salts of plant acids such as malic, meconic, and quinic acids. Some plant alkaloids are combined with sugars, for example, solanine in potato (Solanum tuberosum) and tomatine in tomato (Lycopersicum esculentum). Others occur as amides, for example, piperine from black pepper (Piper nigrum), or as esters, for example, cocaine from coca leaves (Erythroxylum coca). Still other alkaloids occur as quaternary salts or tertiary amine oxides.

While most alkaloids have been isolated from plants, a large number have been isolated from animal sources. They occur in mammals, anurans (frogs, toads), salamanders, arthropods (ants, millipedes, ladybugs, beetles, butterflies), marine organisms, mosses, fungi, and certain bacteria.

Many alkaloids exhibit marked pharmacological activity, and some find important uses in medicine. Atropine, the optically inactive form of hyoscyamine, is used widely in medicine as an antidote to cholinesterase inhibitors such as physostigmine and insecticides of the organophosphate type; it is also used in drying cough secretions. Morphine and codeine are narcotic analgesics, and codeine is also an antitussive agent, less toxic and less habit-forming than morphine. Colchicine, from the corms and seeds of the autumn crocus, is used as a gout suppressant. Caffeine, which occurs in coffee, tea, cocoa, and cola, is a central nervous system stimulant; it is used as a cardiac and respiratory stimulant and as an antidote to barbiturate and morphine poisoning. Emetine, the key alkaloid of ipecac root (Cephaelis ipecacuanha), is used in the treatment of amebic dysentery and other protozoal infections. Epinephrine or adrenaline (see structure), produced in most animal species by the adrenal medulla, is used as a

Naturally occurring organic bases which have marked pharmacological actions in man and other animals. Many are found in plant foods, including potatoes and tomatoes (the Solanum alkaloids), or as the products of fungal action (e.g. ergot), although they also occur in animal foods (e.g. tetrodotoxin in puffer fish, tetramine in shellfish).

Any one of the many nitrogen-containing organic bases derived from plants. The alkaloids are bitter and physiologically active. A number are useful therapeutic agents.

A member of a group of nitrogen-containing compounds that include cocaine, morphine, and nicotine.

One of a large group of small organic compounds, mainly derived from amino acids, and containing nitrogen, found in plants. They are water-soluble, usually bitter in taste and are characterized by powerful physiological activity. Examples are morphine, cocaine, atropine, quinine, nicotine and caffeine. The term is also applied to synthetic substances that have structures similar to plant alkaloids, such as procaine. When treated with acids they are converted to water-soluble salts. In cases of poisoning by alkaloids the recommended antidote is tannic acid, but heavy metal salts and iodine also precipitate them. Includes pyrrolizidine and solanaceous alkaloids.

A plant compound containing nitrogen that, possibly because of its bitter taste, defends plants against predators. Alkaloids also include plant poisons or medicines. Nicotine, cocaine, and quinine are examples of plant alkaloids.

This article is about the chemical compounds alkaloids. For the pharmaceutical company in the Republic of Macedonia, see Alkaloid (company).

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

Contents 1 Alkaloid classifications 2 Physicochemical properties 3 See also 4 References

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

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.

See also

Amine Base (chemistry)

Natural products Secondary metabolite

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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v • d • e Alkaloid groups Indole: 5-MeO-DMT | Dimethyltryptamine | Harmala alkaloids | Psilocin | Psilocybin | Reserpine | Serotonin | Tryptamine | Yohimbine Phenethylamine: Amphetamine | Cathinone | Dopamine | Ephedrine | Mescaline | Methamphetamine | Phenethylamine | Tyramine Purine: Caffeine | Theobromine | Theophylline Pyridine: Coniine Pyrrolidine: Nicotine Quinoline: Quinine Isoquinoline: Codeine | Morphine Tropane: Atropine | Cocaine | Hyoscyamine | Scopolamine Terpenoid: Aconitine | Solanine Betaines: Choline | Muscarine Major families of biochemicals Saccharides/Carbohydrates/Glycosides · Amino acids/Peptides/Proteins/Glycoproteins · Lipids/Terpenes/Steroids/Carotenoids · Alkaloids/Nucleobases/Nucleic acids · Cofactors/Phenylpropanoids/Polyketides/Tetrapyrroles

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