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Skatole or 3-methylindole is an
organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
belonging to the
indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...
family. It occurs naturally in the
feces Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...
of mammals and birds and is the primary contributor to fecal odor. In low
concentration In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'', ...
s, it has a
flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...
y smell and is found in several
flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...
s and
essential oil An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. Essential oils are also known as volatile oils, ethereal oils, aetheroleum, or simply as the ...
s, including those of
orange Orange most often refers to: *Orange (fruit), the fruit of the tree species '' Citrus'' × ''sinensis'' ** Orange blossom, its fragrant flower ** Orange juice *Orange (colour), the color of an orange fruit, occurs between red and yellow in the vi ...
blossom In botany, blossoms are the flowers of stone fruit trees (genus ''Prunus'') and of some other plants with a similar appearance that flower profusely for a period of time in spring. Colloquially, flowers of orange are referred to as such as w ...
s,
jasmine Jasmine (botanical name: ''Jasminum'', pronounced ) is a genus of shrubs and vines in the olive family of Oleaceae. It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are wid ...
, and ''
Ziziphus mauritiana ''Ziziphus mauritiana'', also known as Indian jujube, Indian plum, Chinese date, Chinese apple, ber and dunks is a tropical fruit tree species belonging to the family Rhamnaceae. It is often confused with the closely related jujube, Chinese ju ...
''. It has also been identified in certain
cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...
varieties. It is used as a fragrance and fixative in many
perfume Perfume (, ) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agre ...
s and as an
aroma compound An aroma compound, also known as an odorant, aroma, fragrance, flavoring or flavor, is a chemical compound that has a smell or odor. For an individual chemical or class of chemical compounds to impart a smell or fragrance, it must be sufficien ...
. It is also used in low concentrations in some ice cream as a flavor enhancer. Its name derives from the Greek root ''skato-'', meaning feces. Skatole was discovered in 1877 by the German physician
Ludwig Brieger Ludwig Brieger (1849–1919, Glatze (now Klodzko, Poland)) was a German physician, pathologist, and chemist. Biography After graduating from the gymnasium in Glatz, he studied at the University of Breslau and University of Stratsburg, wher ...
(1849–1919).


Biosynthesis, chemical synthesis, and reactions

Skatole is derived from the amino acid
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 aromat ...
in the digestive tract of mammals. Tryptophan is converted to
indoleacetic acid Indole-3-acetic acid (IAA, 3-IAA) is the most common naturally occurring plant hormone of the auxin class. It is the best known of the auxins, and has been the subject of extensive studies by plant physiologists. IAA is a derivative of indole, con ...
, which
decarboxylate Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is ...
s to give the methylindole. Once it is created in the digestive tract of mammals, it is metabolized by cytochrome P450 enzymes in the liver. Skatole can be synthesized via the
Fischer indole synthesis The Fischer indole synthesis is a chemical reaction that produces the aromatic Heterocyclic compound, heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by ...
. It gives a violet color upon treatment with
potassium ferrocyanide Potassium hexacyanidoferrate(II) is the inorganic compound with formula K4 e(CN)6�3H2O. It is the potassium salt of the coordination complex e(CN)6sup>4−. This salt forms lemon-yellow monoclinic crystals. Synthesis In 1752, the French chemi ...
. Skatole, along with the fecal odorant
indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...
, can be neutralized by combining it with other scents, by producing perfumes or air fresheners that lack skatole and indole. In a manner similar to
noise-cancelling headphones Noise-cancelling headphones are headphones that suppress unwanted ambient sounds using active noise control (ANC). Active noise cancellation makes it possible to listen to audio content without raising the volume excessively. In an aviation envi ...
, the scent produced by the resultant concentrations of skatole and indole relative to other substances in the freshener is thus "in-phase" and perceived as pleasant.


Insect studies

Skatole is one of many compounds that are attractive to males of various species of
orchid bee The tribe Euglossini, in the subfamily Apinae, commonly known as orchid bees or euglossine bees, are the only group of corbiculate bees whose non-parasitic members do not all possess eusocial behavior. Description, distribution, and behavior ...
s, which apparently gather the chemical to synthesize pheromones; it is commonly used as bait for these bees for study. It is also known for being an attractant for the Tasmanian grass grub beetle (''
Aphodius tasmaniae ''Aphodius'' is a genus of beetles in the family Scarabaeidae. In most species both the adults and Larva, larvae are coprophagous (dung feeding) although some species have Herbivore, herbivorous or Saprotrophic nutrition, saprophagous larvae. ' ...
''). Skatole has been shown to be an attractant to
gravid In biology and medicine, gravidity and parity are the number of times a female has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These two terms are usually coupled, sometimes with additional terms, t ...
mosquito Mosquitoes, the Culicidae, are a Family (biology), family of small Diptera, flies consisting of 3,600 species. The word ''mosquito'' (formed by ''Musca (fly), mosca'' and diminutive ''-ito'') is Spanish and Portuguese for ''little fly''. Mos ...
es in both field and laboratory conditions. Because this compound is present in feces, it is found in
combined sewage overflow A combined sewer is a type of gravity sewer with a system of pipes, tunnels, pump stations etc. to transport sewage and urban runoff together to a sewage treatment plant or disposal site. This means that during rain events, the sewage gets dilute ...
s (CSO), as streams and lakes containing CSO water have untreated human and industrial waste. CSO sites are thus of particular interest when studying
mosquito-borne disease Mosquito-borne diseases or mosquito-borne illnesses are diseases caused by bacteria, viruses or parasites transmitted by mosquitoes. Nearly 700 million people contract mosquito-borne illnesses each year, resulting in more than a million death ...
s such as
West Nile virus West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...
. The release of skatole by certain parasitic wasps in the family
Bethylidae The Bethylidae are a family of aculeate wasps in the superfamily Chrysidoidea. As a family, their biology ranges between parasitoid wasps and hunting wasps. Overview Like most of the Chrysidoidea, the Bethylidae are stinging Hymenoptera and mos ...
is used to determine which subfamily the species belongs to. Species of the Epyrinae subfamily release skatole, while those in the Bethylinae subfamily release a different chemical, spiroacetal.


Animal studies

Skatole occurs naturally in the feces of all species of mammals and birds, and in the
bovine Bovines (subfamily Bovinae) comprise a diverse group of 10 genera of medium to large-sized ungulates, including Bos, cattle, bison, African buffalo, Bubalus, water buffalos, and the four-horned and spiral-horned antelopes. The members of this gro ...
rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants. The rumen and the reticulum make up the reticulorumen in ruminant animals. The diverse microbial communities in the rumen allows it to serve as the primary si ...
. Skatole has been shown to cause
pulmonary edema Pulmonary edema (British English: oedema), also known as pulmonary congestion, is excessive fluid accumulation in the tissue or air spaces (usually alveoli) of the lungs. This leads to impaired gas exchange, most often leading to shortness ...
in goats, sheep, rats, and some strains of mice. It appears to selectively target
club cell Club cells, also known as bronchiolar exocrine cells, are low columnar/cuboidal cells with short microvilli, found in the small airways (bronchioles) of the lungs. They were formerly known as ''Clara cells''. Club cells are found in the ciliated ...
s, which are the major site of
cytochrome P450 Cytochromes P450 (P450s or CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that mostly, but not exclusively, function as monooxygenases. However, they are not omnipresent; for examp ...
enzymes in the lungs. These enzymes convert skatole to a reactive intermediate, 3-methyleneindolenine, which damages cells by forming protein
adduct In chemistry, an adduct (; alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is ...
s (see fog fever). With the testicular steroid
androstenone Androstenone (5α-androst-16-en-3-one) is a 16-androstene class steroidal pheromone. It is found in boar's saliva, celery cytoplasm, and truffle fungus. Androstenone was the first mammalian pheromone to be identified. It is found in high concen ...
, skatole is regarded as a principal determinant of boar taint. High amounts of skatole stored in the fat tissue of pigs corresponds with boar taint. To address this, vaccinations with an immunogenic amount of Lawsonia intracellularis antigen are being studied. This antigen reduces the uptake of skatole into the fat of pigs, thus reducing the effect of boar taint. Another method used to address skatole concentration in fat tissue is supplementing the pig's diet with 3% chestnut wood extract. This method showed that intestinal skatole concentration decreased by more than 50%. Skatole contributes to
bad breath Bad breath, also known as halitosis, is a symptom in which a noticeably unpleasant breath odour is present. It can result in anxiety among those affected. It is also associated with depression and symptoms of obsessive compulsive disorder. Th ...
.


Application

Skatole is the starting material in the synthesis of atiprosin.


See also

* 1-Methylindole * 2-Methylindole (methylketol) * 5-Methylindole * 7-Methylindole *
Cadaverine Cadaverine is an organic compound with the formula (CH2)5(NH2)2. Classified as a diamine, it is a colorless liquid with an unpleasant odor. It is present in small quantities in living organisms but is often associated with the putrefaction of Tiss ...


References

{{Authority control, state=expanded Methylindoles Foul-smelling chemicals Perfume ingredients