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Alkaloids are a class of basic,
naturally occurring A natural product is a natural compound or substance produced by a living organism—that is, found in nature. In the broadest sense, natural products include any substance produced by life. Natural products can also be prepared by chemical sy ...
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. T ...
s that contain at least one
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atom. This group also includes some related compounds with neutral and even weakly acidic properties. Some synthetic compounds of similar structure may also be termed alkaloids. In addition to
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...
,
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
and
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
, alkaloids may also contain
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
, sulfur and, more rarely, other elements such as
chlorine Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
,
bromine Bromine is a chemical element with the symbol Br and atomic number 35. It is the third-lightest element in group 17 of the periodic table ( halogens) and is a volatile red-brown liquid at room temperature that evaporates readily to form a simi ...
, and
phosphorus Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
.Chemical Encyclopedia: alkaloids
xumuk.ru
Alkaloids are produced by a large variety of organisms including
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
,
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
,
plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
, and
animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...
s. They can be purified from crude extracts of these organisms by acid-base extraction, or solvent extractions followed by silica-gel
column chromatography Column chromatography in chemistry is a chromatography method used to isolate a single chemical compound from a mixture. Chromatography is able to separate substances based on differential adsorption of compounds to the adsorbent; compounds move th ...
. Alkaloids have a wide range of
pharmacological Pharmacology is a branch of medicine, biology and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous (from within the body) molecule which exerts a biochemica ...
activities including
antimalarial Antimalarial medications or simply antimalarials are a type of antiparasitic chemical agent, often naturally derived, that can be used to treat or to prevent malaria, in the latter case, most often aiming at two susceptible target groups, young ...
(''e.g.''
quinine Quinine is a medication used to treat malaria and babesiosis. This includes the treatment of malaria due to '' Plasmodium falciparum'' that is resistant to chloroquine when artesunate is not available. While sometimes used for nocturnal le ...
), antiasthma (''e.g.''
ephedrine Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in ...
),
anticancer An anticarcinogen (also known as a carcinopreventive agent) is a substance that counteracts the effects of a carcinogen or inhibits the development of cancer. Anticarcinogens are different from anticarcinoma agents (also known as anticancer or an ...
(''e.g.'' homoharringtonine),
cholinomimetic A parasympathomimetic drug, sometimes called a cholinomimetic drug or cholinergic receptor stimulating agent, is a substance that stimulates the parasympathetic nervous system (PSNS). These chemicals are also called cholinergic drugs because ace ...
(''e.g.''
galantamine Galantamine is used for the treatment of cognitive decline in mild to moderate Alzheimer's disease and various other memory impairments. It is an alkaloid that has been isolated from the bulbs and flowers of '' Galanthus nivalis'' (Common snowd ...
),
vasodilatory Vasodilation is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. The process is the opposite of vasoconstriction, ...
(''e.g.''
vincamine Vincamine is a monoterpenoid indole alkaloid found in the leaves of ''Vinca minor'' (lesser periwinkle), comprising about 25-65% of its indole alkaloids by weight. It can also be synthesized from related alkaloids. Uses Vincamine is sold in Eur ...
),
antiarrhythmic Antiarrhythmic agents, also known as cardiac dysrhythmia medications, are a group of pharmaceuticals that are used to suppress abnormally fast rhythms (Tachycardia, tachycardias), such as atrial fibrillation, supraventricular tachycardia and vent ...
(''e.g.''
quinidine Quinidine is a class I antiarrhythmic agent, class IA antiarrhythmic agent used to treat heart rhythm disturbances. It is the enantiomer of Antimalarial medication, antimalarial agent quinine, originally derived from the bark of the cinchona tre ...
), analgesic (''e.g.''
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
),
antibacterial An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
(''e.g.''
chelerythrine Chelerythrine is a benzophenanthridine alkaloid present in the plant ''Chelidonium majus'' (greater celandine). It is a potent, selective, and cell-permeable protein kinase C inhibitor ''in vitro''. And an efficacious antagonist of G-protein-coup ...
), and
antihyperglycemic Drugs used in diabetes treat diabetes mellitus by altering the glucose level in the blood. With the exceptions of insulin, most GLP receptor agonists (liraglutide, exenatide, and others), and pramlintide, all are administered orally and are th ...
activities (''e.g.''
piperine Piperine, along with its isomer chavicine, is the alkaloid responsible for the pungency of black pepper and long pepper. It has been used in some forms of traditional medicine. Preparation Due to its poor solubility in water, piperine is typic ...
). Many have found use in
traditional A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or ...
or
modern medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pract ...
, or as starting points for drug discovery. Other alkaloids possess
psychotropic A psychoactive drug, psychopharmaceutical, psychoactive agent or psychotropic drug is a chemical substance, that changes functions of the nervous system, and results in alterations in perception, mood, consciousness, cognition or behavior. Th ...
(''e.g.''
psilocin Psilocin (also known as 4-HO-DMT, 4-hydroxy DMT, psilocine, psilocyn, or psilotsin) is a substituted tryptamine alkaloid and a serotonergic psychedelic substance. It is present in most psychedelic mushrooms together with its phosphorylated cou ...
) and stimulant activities (''e.g.''
cocaine Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Ameri ...
,
caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
,
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
,
theobromine Theobromine, also known as xantheose, is the principal alkaloid of '' Theobroma cacao'' (cacao plant). Theobromine is slightly water-soluble (330 mg/L) with a bitter taste. In industry, theobromine is used as an additive and precursor to ...
), and have been used in
entheogenic Entheogens are psychoactive substances that induce alterations in perception, mood, consciousness, cognition, or behavior for the purposes of engendering spiritual development or otherwiseRätsch, Christian, ''The Encyclopedia of Psychoact ...
rituals or as recreational drugs. Alkaloids can be
toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
too (''e.g.'' atropine,
tubocurarine Tubocurarine (also known as ''d''-tubocurarine or DTC) is a toxic alkaloid historically known for its use as an arrow poison. In the mid-1900s, it was used in conjunction with an anesthetic to provide skeletal muscle relaxation during surgery or ...
). Although alkaloids act on a diversity of metabolic systems in humans and other animals, they almost uniformly evoke a
bitter taste The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
. The boundary between alkaloids and other nitrogen-containing natural compounds is not clear-cut.Robert A. Meyers ''Encyclopedia of Physical Science and Technology'' – Alkaloids, 3rd edition. Compounds like
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. ...
s,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s,
nucleotide Nucleotides are organic molecules consisting of a nucleoside and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both of which are essential biomolecule ...
s, nucleic acid,
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...
s, and
antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...
are usually not called alkaloids. Natural compounds containing nitrogen in the
exocyclic In organic chemistry, an alicyclic compound contains one or more all-carbon rings which may be either saturated or unsaturated, but do not have aromatic character. Alicyclic compounds may have one or more aliphatic side chains attached. The ...
position ( mescaline, serotonin, dopamine, etc.) are usually classified as
amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen Hydrogen is the chemical element wi ...
s rather than as alkaloids. Some authors, however, consider alkaloids a special case of amines. Aniszewski, p. 110


Naming

The name "alkaloids" (german: Alkaloide, links=no) was introduced in 1819 by the German chemist Carl Friedrich Wilhelm Meißner, and is derived from late Latin root and the Greek-language suffix -('like').In the penultimate sentence of his article, W. Meissner (1819) "Über Pflanzenalkalien: II. Über ein neues Pflanzenalkali (Alkaloid)" (On plant alkalis: II. On a new plant alkali (alkaloid)), ''Journal für Chemie und Physik'', 25 : 379–381 ; available on-line at:
Hathi Trust
– Meissner wrote: "Überhaupt scheint es mir auch angemessen, die bis jetzt bekannten Pflanzenstoffe nicht mit dem Namen Alkalien, sondern Alkaloide zu belegen, da sie doch in manchen Eigenschaften von den Alkalien sehr abweichen, sie würden daher in dem Abschnitt der Pflanzenchemie vor den Pflanzensäuren ihre Stelle finden." (I.e., "In general, it seems appropriate to me to impose on the currently known plant substances not the name 'alkalis' but 'alkaloids', since they differ greatly in some properties from the alkalis; among the chapters of plant chemistry, they would therefore find their place before plant acids ince 'Alkaloid' would precede 'Säure' (acid) but follow 'Alkalien'.)
However, the term came into wide use only after the publication of a review article, by Oscar Jacobsen in the chemical dictionary of Albert Ladenburg in the 1880s. There is no unique method for naming alkaloids.
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p. 5
Many individual names are formed by adding the suffix "ine" to the species or genus name. For example, atropine is isolated from the plant '' Atropa belladonna''; strychnine is obtained from the seed of the Strychnine tree (''Strychnos nux-vomica'' L.). Where several alkaloids are extracted from one plant their names are often distinguished by variations in the suffix: "idine", "anine", "aline", "inine" etc. There are also at least 86 alkaloids whose names contain the root "vin" because they are extracted from ''
vinca ''Vinca'' (; Latin: ''vincire'' "to bind, fetter") is a genus of flowering plants in the family Apocynaceae, native to Europe, northwest Africa and southwest Asia. The English name periwinkle is shared with the related genus ''Catharanthus'' (an ...
'' plants such as ''Vinca rosea'' (''
Catharanthus roseus ''Catharanthus roseus'', commonly known as bright eyes, Cape periwinkle, graveyard plant, Madagascar periwinkle, old maid, pink periwinkle, rose periwinkle, is a species of flowering plant in the family Apocynaceae. It is native and endemic to M ...
''); these are called ''vinca'' alkaloids.


History

Alkaloid-containing plants have been used by humans since ancient times for therapeutic and recreational purposes. For example, medicinal plants have been known in
Mesopotamia Mesopotamia ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن or ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of Western Asia situated within the Tigris–Euphrates river system, in the northern part of the ...
from about 2000 BC. Aniszewski, p. 182 The ''
Odyssey The ''Odyssey'' (; grc, Ὀδύσσεια, Odýsseia, ) is one of two major ancient Greek epic poems attributed to Homer. It is one of the oldest extant works of literature still widely read by modern audiences. As with the ''Iliad'', th ...
'' of Homer referred to a gift given to Helen by the Egyptian queen, a drug bringing oblivion. It is believed that the gift was an opium-containing drug. A Chinese book on houseplants written in 1st–3rd centuries BC mentioned a medical use of
ephedra Ephedra may refer to: * Ephedra (medicine), a medicinal preparation from the plant ''Ephedra sinica'' * ''Ephedra'' (plant), genus of gymnosperm shrubs See also * Ephedrine Ephedrine is a central nervous system (CNS) stimulant that is of ...
and
opium poppies Opium (or poppy tears, scientific name: ''Lachryma papaveris'') is dried latex obtained from the seed capsules of the opium poppy ''Papaver somniferum''. Approximately 12 percent of opium is made up of the analgesic alkaloid morphine, which i ...
. Also,
coca Coca is any of the four cultivated plants in the family Erythroxylaceae, native to western South America. Coca is known worldwide for its psychoactive alkaloid, cocaine. The plant is grown as a cash crop in the Argentine Northwest, Bolivia, ...
leaves have been used by South American Indians since ancient times. Extracts from plants containing toxic alkaloids, such as
aconitine Aconitine is an alkaloid toxin produced by various plant species belonging to the genus ''Aconitum'' (family Ranunculaceae), known also commonly by the names wolfsbane and monkshood. Monkshood is notorious for its toxic properties. Aconitine is ...
and
tubocurarine Tubocurarine (also known as ''d''-tubocurarine or DTC) is a toxic alkaloid historically known for its use as an arrow poison. In the mid-1900s, it was used in conjunction with an anesthetic to provide skeletal muscle relaxation during surgery or ...
, were used since antiquity for poisoning arrows. Studies of alkaloids began in the 19th century. In 1804, the German chemist
Friedrich Sertürner Friedrich Wilhelm Adam Sertürner (19 June 1783 – 20 February 1841) was a German pharmacist and a pioneer of alkaloid chemistry. He is best known for his discovery of morphine in 1804. Biography Friedrich Wilhelm Adam Sertürner was born to J ...
isolated from opium a "soporific principle" ( la, principium somniferum, links=no), which he called "morphium", referring to
Morpheus Morpheus ('Fashioner', derived from the grc, μορφή meaning 'form, shape') is a god associated with sleep and dreams. In Ovid's ''Metamorphoses'' he is the son of Somnus and appears in dreams in human form. From the Middle Ages, the name b ...
, the Greek god of dreams; in German and some other Central-European languages, this is still the name of the drug. The term "morphine", used in English and French, was given by the French physicist
Joseph Louis Gay-Lussac Joseph Louis Gay-Lussac (, , ; 6 December 1778 – 9 May 1850) was a French chemist and physicist. He is known mostly for his discovery that water is made of two parts hydrogen and one part oxygen (with Alexander von Humboldt), for two laws ...
. A significant contribution to the chemistry of alkaloids in the early years of its development was made by the French researchers
Pierre Joseph Pelletier Pierre-Joseph Pelletier (, , ; 22 March 1788 – 19 July 1842) was a French chemist and pharmacist who did notable research on vegetable alkaloids, and was the co-discoverer with Joseph Bienaimé Caventou of quinine, caffeine, and strychnine ...
and
Joseph Bienaimé Caventou Joseph Bienaimé Caventou (30 June 1795 – 5 May 1877) was a French pharmacist. He was a professor at the École de Pharmacie (School of Pharmacy) in Paris. He collaborated with Pierre-Joseph Pelletier in a Parisian laboratory located behind an ...
, who discovered
quinine Quinine is a medication used to treat malaria and babesiosis. This includes the treatment of malaria due to '' Plasmodium falciparum'' that is resistant to chloroquine when artesunate is not available. While sometimes used for nocturnal le ...
(1820) and strychnine (1818). Several other alkaloids were discovered around that time, including
xanthine Xanthine ( or ; archaically xanthic acid; systematic name 3,7-dihydropurine-2,6-dione) is a purine base found in most human body tissues and fluids, as well as in other organisms. Several stimulants are derived from xanthine, including caffeine ...
(1817), atropine (1819),
caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
(1820),
coniine Coniine is a poisonous chemical compound, an alkaloid present in and isolable from poison hemlock ('' Conium maculatum''), where its presence has been a source of significant economic, medical, and historico-cultural interest; coniine is also prod ...
(1827),
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
(1828),
colchicine Colchicine is a medication used to treat gout and Behçet's disease. In gout, it is less preferred to NSAIDs or steroids. Other uses for colchicine include the management of pericarditis and familial Mediterranean fever. Colchicine is taken b ...
(1833),
sparteine Sparteine is a class 1a antiarrhythmic agent; a sodium channel blocker. It is an alkaloid and can be extracted from scotch broom. It is the predominant alkaloid in '' Lupinus mutabilis'', and is thought to chelate the bivalent cations calcium and ...
(1851), and
cocaine Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Ameri ...
(1860). The development of the chemistry of alkaloids was accelerated by the emergence of
spectroscopic Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
and
chromatographic In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
methods in the 20th century, so that by 2008 more than 12,000 alkaloids had been identified. The first complete synthesis of an alkaloid was achieved in 1886 by the German chemist Albert Ladenburg. He produced
coniine Coniine is a poisonous chemical compound, an alkaloid present in and isolable from poison hemlock ('' Conium maculatum''), where its presence has been a source of significant economic, medical, and historico-cultural interest; coniine is also prod ...
by reacting 2-methylpyridine with acetaldehyde and reducing the resulting 2-propenyl pyridine with sodium.


Classifications

Compared with most other classes of natural compounds, alkaloids are characterized by a great structural diversity. There is no uniform classification.
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p. 11
Initially, when knowledge of chemical structures was lacking, botanical classification of the source plants was relied on. This classification is now considered obsolete. More recent classifications are based on similarity of the carbon skeleton (''e.g.'',
indole Indole is an aromatic heterocyclic organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other c ...
-,
isoquinoline Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoqu ...
-, and
pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a ...
-like) or biochemical precursor (
ornithine Ornithine is a non-proteinogenic amino acid that plays a role in the urea cycle. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency. The radical is ornithyl. Role in urea cycle L-Ornithine is one of the produ ...
, lysine,
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
,
tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...
, etc.). However, they require compromises in borderline cases; for example,
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
contains a pyridine fragment from
nicotinamide Niacinamide or Nicotinamide (NAM) is a form of vitamin B3 found in food and used as a dietary supplement and medication. As a supplement, it is used by mouth to prevent and treat pellagra (niacin deficiency). While nicotinic acid (niacin) may ...
and a pyrrolidine part from ornithine and therefore can be assigned to both classes. Dewick, p. 307 Alkaloids are often divided into the following major groups: # "True alkaloids" contain
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
in the
heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis, properties, and ...
and originate from
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s. Plemenkov, p. 223 Their characteristic examples are atropine,
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
, and
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
. This group also includes some alkaloids that besides the nitrogen heterocycle contain
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
(''e.g.'', evonine) or peptide fragments (''e.g.''
ergotamine Ergotamine, sold under the brand names Cafergot (with caffeine) and Ergomar among others, is an ergopeptine and part of the ergot family of alkaloids; it is structurally and biochemically closely related to ergoline. It possesses structural sim ...
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p. 84
). The piperidine alkaloids
coniine Coniine is a poisonous chemical compound, an alkaloid present in and isolable from poison hemlock ('' Conium maculatum''), where its presence has been a source of significant economic, medical, and historico-cultural interest; coniine is also prod ...
and coniceine may be regarded as true alkaloids (rather than pseudoalkaloids: see below)
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p. 31
although they do not originate from amino acids. Dewick, p. 381 # "Protoalkaloids", which contain
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
(but not the nitrogen heterocycle) and also originate from amino acids. Examples include mescaline,
adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands an ...
and
ephedrine Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in ...
. # Polyamine alkaloids – derivatives of
putrescine Putrescine is an organic compound with the formula (CH2)4(NH2)2. It is a colorless solid that melts near room temperature. It is classified as a diamine. Together with cadaverine, it is largely responsible for the foul odor of putrefying flesh, ...
,
spermidine Spermidine is a polyamine compound () found in ribosomes and living tissues and having various metabolic functions within organisms. It was originally isolated from semen. Function Spermidine is an aliphatic polyamine. Spermidine synthase (SP ...
, and
spermine Spermine is a polyamine involved in cellular metabolism that is found in all eukaryotic cells. The precursor for synthesis of spermine is the amino acid ornithine. It is an essential growth factor in some bacteria as well. It is found as a p ...
. # Peptide and cyclopeptide alkaloids. # Pseudoalkaloids – alkaloid-like compounds that do not originate from amino acids. This group includes
terpene Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ...
-like and steroid-like alkaloids, as well as
purine Purine is a heterocyclic aromatic organic compound that consists of two rings ( pyrimidine and imidazole) fused together. It is water-soluble. Purine also gives its name to the wider class of molecules, purines, which include substituted purines ...
-like alkaloids such as
caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
,
theobromine Theobromine, also known as xantheose, is the principal alkaloid of '' Theobroma cacao'' (cacao plant). Theobromine is slightly water-soluble (330 mg/L) with a bitter taste. In industry, theobromine is used as an additive and precursor to ...
, theacrine and
theophylline Theophylline, also known as 1,3-dimethylxanthine, is a phosphodiesterase inhibiting drug used in therapy for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma under a variety of brand names. As a member of the ...
. Aniszewski, p. 12 Some authors classify as pseudoalkaloids such compounds such as
ephedrine Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in ...
and cathinone. Those originate from the amino acid phenylalanine, but acquire their nitrogen atom not from the amino acid but through
transamination Transamination is a chemical reaction that transfers an amino group to a ketoacid to form new amino acids. This pathway is responsible for the deamination of most amino acids. This is one of the major degradation pathways which convert essential ...
. Dewick, p. 382 Some alkaloids do not have the carbon skeleton characteristic of their group. So, galanthamine and homoaporphines do not contain
isoquinoline Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoqu ...
fragment, but are, in general, attributed to isoquinoline alkaloids. Main classes of monomeric alkaloids are listed in the table below:


Properties

Most alkaloids contain oxygen in their molecular structure; those compounds are usually colorless crystals at ambient conditions. Oxygen-free alkaloids, such as
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
or
coniine Coniine is a poisonous chemical compound, an alkaloid present in and isolable from poison hemlock ('' Conium maculatum''), where its presence has been a source of significant economic, medical, and historico-cultural interest; coniine is also prod ...
, are typically volatile, colorless, oily liquids. Grinkevich, p. 131 Some alkaloids are colored, like
berberine Berberine is a quaternary ammonium salt from the protoberberine group of benzylisoquinoline alkaloids found in such plants as ''Berberis vulgaris'' (barberry), '' Berberis aristata'' (tree turmeric), '' Mahonia aquifolium'' (Oregon grape), '' Hyd ...
(yellow) and
sanguinarine Sanguinarine is a polycyclic quaternary alkaloid. It is extracted from some plants, including the bloodroot plant, from whose taxonomic name, ''Sanguinaria canadensis,'' its name is drawn; the Mexican prickly poppy (''Argemone mexicana''); ''Chel ...
(orange). Most alkaloids are weak bases, but some, such as
theobromine Theobromine, also known as xantheose, is the principal alkaloid of '' Theobroma cacao'' (cacao plant). Theobromine is slightly water-soluble (330 mg/L) with a bitter taste. In industry, theobromine is used as an additive and precursor to ...
and
theophylline Theophylline, also known as 1,3-dimethylxanthine, is a phosphodiesterase inhibiting drug used in therapy for respiratory diseases such as chronic obstructive pulmonary disease (COPD) and asthma under a variety of brand names. As a member of the ...
, are
amphoteric In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used. One type of amphoteric species are amphipro ...
.G. A. Spille
''Caffeine''
CRC Press, 1997
Many alkaloids dissolve poorly in water but readily dissolve in
organic solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s, such as
diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
, chloroform or
1,2-dichloroethane The chemical compound 1,2-dichloroethane, commonly known as ethylene dichloride (EDC), is a chlorinated hydrocarbon. It is a colourless liquid with a chloroform-like odour. The most common use of 1,2-dichloroethane is in the production of vin ...
.
Caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
,
cocaine Cocaine (from , from , ultimately from Quechua: ''kúka'') is a central nervous system (CNS) stimulant mainly used recreationally for its euphoric effects. It is primarily obtained from the leaves of two Coca species native to South Ameri ...
, codeine and
nicotine Nicotine is a natural product, naturally produced alkaloid in the nightshade family of plants (most predominantly in tobacco and ''Duboisia hopwoodii'') and is widely used recreational drug use, recreationally as a stimulant and anxiolytic. As ...
are slightly soluble in water (with a solubility of ≥1g/L), whereas others, including
morphine Morphine is a strong opiate that is found naturally in opium, a dark brown resin in poppies (''Papaver somniferum''). It is mainly used as a pain medication, and is also commonly used recreationally, or to make other illicit opioids. T ...
and
yohimbine Yohimbine (), also known as quebrachine, is an indole alkaloid derived from the bark of the African tree '' Pausinystalia johimbe''; also from the bark of the unrelated South American tree ''Aspidosperma quebracho-blanco''. Yohimbine is an α2 ...
are very slightly water-soluble (0.1–1 g/L). Alkaloids and acids form salts of various strengths. These salts are usually freely soluble in water and
ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...
and poorly soluble in most organic solvents. Exceptions include scopolamine hydrobromide, which is soluble in organic solvents, and the water-soluble quinine sulfate. Most alkaloids have a bitter taste or are poisonous when ingested. Alkaloid production in plants appeared to have evolved in response to feeding by herbivorous animals; however, some animals have evolved the ability to detoxify alkaloids. Some alkaloids can produce developmental defects in the offspring of animals that consume but cannot detoxify the alkaloids. One example is the alkaloid
cyclopamine Cyclopamine (11-deoxojervine) is a naturally occurring chemical that belongs in the family of steroidal alkaloids. It is a teratogen isolated from the corn lily ('' Veratrum californicum'') that causes fatal birth defects. It prevents the embryo ...
, produced in the leaves of corn lily. During the 1950s, up to 25% of lambs born by sheep that had grazed on corn lily had serious facial deformations. These ranged from deformed jaws to
cyclopia Cyclopia (named after the Greek mythology character cyclopes) is the most extreme form of holoprosencephaly and is a congenital disorder (birth defect) characterized by the failure of the embryonic prosencephalon to properly divide the orbits of ...
(see picture). After decades of research, in the 1980s, the compound responsible for these deformities was identified as the alkaloid 11-deoxyjervine, later renamed to cyclopamine.


Distribution in nature

Alkaloids are generated by various living organisms, especially by
higher plants Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...
 – about 10 to 25% of those contain alkaloids. Therefore, in the past the term "alkaloid" was associated with plants.
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p.4
The alkaloids content in plants is usually within a few percent and is inhomogeneous over the plant tissues. Depending on the type of plants, the maximum concentration is observed in the leaves (for example, black henbane),
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particu ...
s or
seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...
s ( Strychnine tree), root (''
Rauvolfia serpentina ''Rauvolfia serpentina'', the Indian snakeroot, devil pepper, or serpentine wood, is a species of flower in the milkweed family Apocynaceae. It is native to the Indian subcontinent and East Asia (from India to Indonesia). ''Rauvolfia'' is a pe ...
'') or bark ( cinchona). Furthermore, different tissues of the same plants may contain different alkaloids. Beside plants, alkaloids are found in certain types of
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...
, such as
psilocybin Psilocybin ( , ) is a naturally occurring psychedelic prodrug compound produced by more than 200 species of fungi. The most potent are members of the genus ''Psilocybe'', such as '' P. azurescens'', '' P. semilanceata'', and '' P.&nbs ...
in the fungus of the genus ''
Psilocybe ''Psilocybe'' ( ) is a genus of gilled mushrooms, growing worldwide, in the family Hymenogastraceae. Most or nearly all species contain the psychedelic compounds psilocybin and psilocin. Taxonomy Taxonomic history A 2002 study of the mol ...
'', and in animals, such as
bufotenin Bufotenin (5-HO-DMT, bufotenine) is a tryptamine derivative - more specifically, a DMT derivative - related to the neurotransmitter serotonin. It is an alkaloid found in some species of toads (especially the skin), mushrooms and plants. ...
in the skin of some toads and a number of insects, markedly ants. Many marine organisms also contain alkaloids. Some
amines In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent such ...
, such as
adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands an ...
and serotonin, which play an important role in higher animals, are similar to alkaloids in their structure and biosynthesis and are sometimes called alkaloids.


Extraction

Because of the structural diversity of alkaloids, there is no single method of their extraction from natural raw materials.
Hesse Hesse (, , ) or Hessia (, ; german: Hessen ), officially the State of Hessen (german: links=no, Land Hessen), is a state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt. Two other major historic cities are Dar ...
, p. 116
Most methods exploit the property of most alkaloids to be soluble in organic solvents but not in water, and the opposite tendency of their salts. Most plants contain several alkaloids. Their mixture is extracted first and then individual alkaloids are separated. Grinkevich, p. 132 Plants are thoroughly ground before extraction. Most alkaloids are present in the raw plants in the form of salts of organic acids. The extracted alkaloids may remain salts or change into bases. Base extraction is achieved by processing the raw material with alkaline solutions and extracting the alkaloid bases with organic solvents, such as 1,2-dichloroethane, chloroform, diethyl ether or benzene. Then, the impurities are dissolved by weak acids; this converts alkaloid bases into salts that are washed away with water. If necessary, an aqueous solution of alkaloid salts is again made alkaline and treated with an organic solvent. The process is repeated until the desired purity is achieved. In the acidic extraction, the raw plant material is processed by a weak acidic solution (''e.g.'', acetic acid in water, ethanol, or methanol). A base is then added to convert alkaloids to basic forms that are extracted with organic solvent (if the extraction was performed with alcohol, it is removed first, and the remainder is dissolved in water). The solution is purified as described above. Alkaloids are separated from their mixture using their different solubility in certain solvents and different reactivity with certain reagents or by
distillation Distillation, or classical distillation, is the process of separating the components or substances from a liquid mixture by using selective boiling and condensation, usually inside an apparatus known as a still. Dry distillation is the heat ...
. A number of alkaloids are identified from
insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three ...
s, among which the
fire ant Fire ants are several species of ants in the genus ''Solenopsis'', which includes over 200 species. ''Solenopsis'' are stinging ants, and most of their common names reflect this, for example, ginger ants and tropical fire ants. Many of the nam ...
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...
alkaloids known as
solenopsin Solenopsin is a lipophilic alkaloid with the molecular formula C17H35N found in the venom of fire ants (''Solenopsis''). It is considered the primary toxin in the venom and may be the component responsible for the cardiorespiratory failure in pe ...
s have received greater attention from researchers. These insect alkaloids can be efficiently extracted by solvent immersion of live fire ants or by centrifugation of live ants followed by silica-gel chromatography purification. Tracking and dosing the extracted solenopsin ant alkaloids has been described as possible based on their absorbance peak around 232 nanometers.


Biosynthesis

Biological precursors of most alkaloids are
amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, such as
ornithine Ornithine is a non-proteinogenic amino acid that plays a role in the urea cycle. Ornithine is abnormally accumulated in the body in ornithine transcarbamylase deficiency. The radical is ornithyl. Role in urea cycle L-Ornithine is one of the produ ...
, lysine, phenylalanine,
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acids that are used by cells to synthesize proteins. It is a non-essential amino acid with a polar side group. The word "tyrosine" is from the G ...
,
tryptophan Tryptophan (symbol Trp or W) is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α-amino group, an α-carboxylic acid group, and a side chain indole, making it a polar molecule with a non-polar aromatic ...
,
histidine Histidine (symbol His or H) is an essential amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated –NH3+ form under biological conditions), a carboxylic acid group (which is in the d ...
, aspartic acid, and
anthranilic acid Anthranilic acid is an aromatic acid with the formula C6H4(NH2)(CO2H) and has a sweetish taste. The molecule consists of a benzene ring, ''ortho''-substituted with a carboxylic acid and an amine. As a result of containing both acidic and basic ...
. Plemenkov, p. 253 Nicotinic acid can be synthesized from tryptophan or aspartic acid. Ways of alkaloid biosynthesis are too numerous and cannot be easily classified. However, there are a few typical reactions involved in the biosynthesis of various classes of alkaloids, including synthesis of
Schiff bases In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimine ...
and
Mannich reaction In organic chemistry, the Mannich reaction is a three-component organic reaction that involves the amino alkylation of an acidic proton next to a carbonyl () functional group by formaldehyde () and a primary or secondary amine () or ammonia (). ...
.


Synthesis of Schiff bases

Schiff bases can be obtained by reacting amines with ketones or aldehydes. These reactions are a common method of producing C=N bonds. Dewick, p. 19 In the biosynthesis of alkaloids, such reactions may take place within a molecule, such as in the synthesis of piperidine:


Mannich reaction

An integral component of the Mannich reaction, in addition to an amine and a
carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containi ...
compound, is a carbanion, which plays the role of the nucleophile in the nucleophilic addition to the ion formed by the reaction of the amine and the carbonyl. The Mannich reaction can proceed both intermolecularly and intramolecularly:


Dimer alkaloids

In addition to the described above monomeric alkaloids, there are also
dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ...
ic, and even trimeric and
tetramer A tetramer () ('' tetra-'', "four" + '' -mer'', "parts") is an oligomer formed from four monomers or subunits. The associated property is called ''tetramery''. An example from inorganic chemistry is titanium methoxide with the empirical formula ...
ic alkaloids formed upon condensation of two, three, and four monomeric alkaloids. Dimeric alkaloids are usually formed from monomers of the same type through the following mechanisms: *
Mannich reaction In organic chemistry, the Mannich reaction is a three-component organic reaction that involves the amino alkylation of an acidic proton next to a carbonyl () functional group by formaldehyde () and a primary or secondary amine () or ammonia (). ...
, resulting in, ''e.g.'', voacamine *
Michael reaction In organic chemistry, the Michael reaction or Michael addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon ...
(villalstonine) * Condensation of aldehydes with amines (toxiferine) * Oxidative addition of phenols (dauricine, tubocurarine) *
Lactonization Lactones are cyclic carboxylic esters, containing a 1-oxacycloalkan-2-one structure (), or analogues having unsaturation or heteroatoms replacing one or more carbon atoms of the ring. Lactones are formed by intramolecular esterification of the co ...
(carpaine). File:Voacamine chemical structure.png,
Voacamine Voacamine, also known under the older names voacanginine and vocamine, is a naturally occurring dimeric indole alkaloid of the secologanin type, found in a number of plants, including ''Voacanga africana'' and ''Tabernaemontana divaricata''. It ...
File:Villalstonine.svg, Villalstonine File:Toxiferine I.png,
Toxiferine Toxiferine (C-toxiferine I) is a curare toxin. It is a bisindole alkaloid derived from ''Strychnos toxifera'' and a nicotinic acetylcholine receptor antagonist. This alkaloid is the main toxic component of Calabash curare, and one of the most t ...
File:Dauricine.svg, Dauricine File:Tubocurarine.svg,
Tubocurarine Tubocurarine (also known as ''d''-tubocurarine or DTC) is a toxic alkaloid historically known for its use as an arrow poison. In the mid-1900s, it was used in conjunction with an anesthetic to provide skeletal muscle relaxation during surgery or ...
File:Carpaine.png, Carpaine
There are also dimeric alkaloids formed from two distinct monomers, such as the ''vinca'' alkaloids
vinblastine Vinblastine (VBL), sold under the brand name Velban among others, is a chemotherapy medication, typically used with other medications, to treat a number of types of cancer. This includes Hodgkin's lymphoma, non-small cell lung cancer, bladder ca ...
and vincristine, which are formed from the coupling of catharanthine and
vindoline Vindoline is a chemical precursor to vinblastine. Vindoline is formed through biosynthesis from Tabersonine Tabersonine is a terpene indole alkaloid found in the medicinal plant ''Catharanthus roseus'' and also in the genus Voacanga (both taxa b ...
. The newer
semi-synthetic Semisynthesis, or partial chemical synthesis, is a type of chemical synthesis that uses chemical compounds isolated from natural sources (such as microbial cell cultures or plant material) as the starting materials to produce novel compounds with ...
chemotherapeutic agent
vinorelbine Vinorelbine (NVB), sold under the brand name Navelbine among others, is a chemotherapy medication used to treat a number of types of cancer. This includes breast cancer and non-small cell lung cancer. It is given by injection into a vein or by mou ...
is used in the treatment of
non-small-cell lung cancer Non-small-cell lung cancer (NSCLC) is any type of epithelial lung cancer other than small-cell lung carcinoma (SCLC). NSCLC accounts for about 85% of all lung cancers. As a class, NSCLCs are relatively insensitive to chemotherapy, compared to s ...
. It is another derivative dimer of vindoline and catharanthine and is synthesised from
anhydrovinblastine Vinorelbine (NVB), sold under the brand name Navelbine among others, is a chemotherapy medication used to treat a number of types of cancer. This includes breast cancer and non-small cell lung cancer. It is given by injection into a vein or by mou ...
, starting either from leurosine or the monomers themselves.


Biological role

Alkaloids are among the most important and best-known
secondary metabolites Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, e.g. bacteria, fungi, animals, or plants, which are not directly involved in the nor ...
, i.e. biogenic substances not directly involved in the normal growth,
development Development or developing may refer to: Arts *Development hell, when a project is stuck in development *Filmmaking, development phase, including finance and budgeting *Development (music), the process thematic material is reshaped * Photograph ...
, or reproduction of the organism. Instead, they generally mediate ecological
interactions Interaction is action that occurs between two or more objects, with broad use in philosophy and the sciences. It may refer to: Science * Interaction hypothesis, a theory of second language acquisition * Interaction (statistics) * Interactions o ...
, which may produce a selective advantage for the organism by increasing its
survivability Survivability is the ability to remain alive or continue to exist. The term has more specific meaning in certain contexts. Ecological Following disruptive forces such as flood, fire, disease, war, or climate change some species of flora, fauna, ...
or
fecundity Fecundity is defined in two ways; in human demography, it is the potential for reproduction of a recorded population as opposed to a sole organism, while in population biology, it is considered similar to fertility, the natural capability to pr ...
. In some cases their function, if any, remains unclear. An early hypothesis, that alkaloids are the final products of
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...
in plants, as
urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important ...
and
uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown ...
are in mammals, was refuted by the finding that their concentration fluctuates rather than steadily increasing.Robert A. Meyers ''Encyclopedia of Physical Science and Technology'' – Alkaloids, 3rd edition. Most of the known functions of alkaloids are related to protection. For example,
aporphine Aporphine is an alkaloid with the chemical formula . The IUPAC (International Union of Pure and Applied Chemistry) name of aporphine is ''6-methyl-5,6,6a,7-tetrahydro-4H-dibenzo e,guinoline.'' It is the core chemical substructure of the aporphine ...
alkaloid liriodenine produced by the
tulip tree ''Liriodendron'' () is a genus of two species of characteristically large trees, deciduous over most of their populations, in the magnolia family (Magnoliaceae). These trees are widely known by the common name tulip tree or tuliptree for their ...
protects it from parasitic mushrooms. In addition, the presence of alkaloids in the plant prevents insects and
chordate A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...
animals from eating it. However, some animals are adapted to alkaloids and even use them in their own metabolism. Such alkaloid-related substances as serotonin, dopamine and
histamine Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological functions in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus. Since histamine was discovered ...
are important neurotransmitters in animals. Alkaloids are also known to regulate plant growth. One example of an organism that uses alkaloids for protection is the ''
Utetheisa ornatrix ''Utetheisa ornatrix'', also called the bella moth, ornate moth or rattlebox moth is a moth of the subfamily Arctiinae. It is aposematically colored ranging from pink, red, orange and yellow to white coloration with black markings arranged in va ...
'', more commonly known as the ornate moth. Pyrrolizidine alkaloids render these larvae and adult moths unpalatable to many of their natural enemies like coccinelid beetles, green lacewings, insectivorous hemiptera and insectivorous bats. Another example of alkaloids being utilized occurs in the poison hemlock moth (''Agonopterix alstroemeriana).'' This moth feeds on its highly toxic and alkaloid-rich host plant
poison hemlock ''Conium maculatum'', colloquially known as hemlock, poison hemlock or wild hemlock, is a highly poisonous biennial herbaceous flowering plant in the carrot family Apiaceae, native to Europe and North Africa. A hardy plant capable of living in ...
(''Conium maculatum'') during its larval stage. ''A. alstroemeriana'' may benefit twofold from the toxicity of the naturally-occurring alkaloids, both through the unpalatability of the species to predators and through the ability of ''A. alstroemeriana'' to recognize ''Conium maculatum'' as the correct location for oviposition. A
fire ant Fire ants are several species of ants in the genus ''Solenopsis'', which includes over 200 species. ''Solenopsis'' are stinging ants, and most of their common names reflect this, for example, ginger ants and tropical fire ants. Many of the nam ...
venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a st ...
alkaloid known as
solenopsin Solenopsin is a lipophilic alkaloid with the molecular formula C17H35N found in the venom of fire ants (''Solenopsis''). It is considered the primary toxin in the venom and may be the component responsible for the cardiorespiratory failure in pe ...
has been demonstrated to protect queens of Red imported fire ant, invasive fire ants during the foundation of new nests, thus playing a central role in the spread of this pest ant species around the world.


Applications


In medicine

Medical use of alkaloid-containing plants has a long history, and, thus, when the first alkaloids were isolated in the 19th century, they immediately found application in clinical practice. Many alkaloids are still used in medicine, usually in the form of salts widely used including the following: Many synthetic and semisynthetic drugs are structural modifications of the alkaloids, which were designed to enhance or change the primary effect of the drug and reduce unwanted side-effects. For example, naloxone, an opioid receptor receptor antagonist, antagonist, is a derivative of thebaine that is present in opium. File:Thebaine skeletal.svg, Thebaine File:Naloxone.svg, Naloxone


In agriculture

Prior to the development of a wide range of relatively low-toxic synthetic pesticides, some alkaloids, such as salts of nicotine and anabasine, were used as insecticides. Their use was limited by their high toxicity to humans.


Use as psychoactive drugs

Preparations of plants containing alkaloids and their extracts, and later pure alkaloids, have long been used as Psychoactive drug, psychoactive substances. Cocaine,
caffeine Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine to ...
, and cathinone are stimulants of the central nervous system. Mescaline and many indole alkaloids (such as
psilocybin Psilocybin ( , ) is a naturally occurring psychedelic prodrug compound produced by more than 200 species of fungi. The most potent are members of the genus ''Psilocybe'', such as '' P. azurescens'', '' P. semilanceata'', and '' P.&nbs ...
, dimethyltryptamine and ibogaine) have hallucinogenic effect. Morphine and codeine are strong narcotic pain killers. There are alkaloids that do not have strong psychoactive effect themselves, but are precursor (chemistry), precursors for semi-synthetic psychoactive drugs. For example,
ephedrine Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in ...
and pseudoephedrine are used to produce methcathinone and methamphetamine.#Veselovskaya, Veselovskaya, pp. 51–52 Thebaine is used in the synthesis of many painkillers such as oxycodone.


See also

* Amine * Base (chemistry) * List of poisonous plants * Mayer's reagent * Natural products * Palau'amine * Secondary metabolite


Explanatory notes


Citations


General and cited references

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External links

* * {{Authority control Alkaloids,