Skatole or 3-methylindole is an

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. The ...

belonging to the indole family. It occurs naturally in the

feces Feces ( or faeces), known colloquially and in slang as poo and poop, 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 large intestine. Feces contain a relati ...

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'', an ...

s, it has a

flower A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants (plants of the division Angiospermae). The biological function of a flower is to facilitate reproduction, usually by providing a mechani ...

y smell and is found in several

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 o ...

s, including those of orange

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 wel ...

jasmine Jasmine ( taxonomic name: ''Jasminum''; , ) is a genus of shrubs and vines in the olive family (Oleaceae). It contains around 200 species native to tropical and warm temperate regions of Eurasia, Africa, and Oceania. Jasmines are widely cultiva ...

, and '' Ziziphus mauritiana''. It is used as a fragrance and fixative in many

perfume Perfume (, ; french: parfum) is a mixture of fragrant essential oils or aroma compounds (fragrances), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent. Th ...

s and as an aroma compound. Its name derives from the Greek root ''skato-'', meaning feces. Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919).

Original: "''Ich habe mich zuerst mit der Untersuchung der flüchtigen Bestandtheile der Excremente aus sauerer Lösung beschäftigt. Es wurden dabei die flüchtigen Fettsäuren: Essigsäure, normale und Isobuttersäure, sowie die aromatischen Substanzen: Phenol, Indol und eine neue dem Indol verwandte Substanz, die ich Skatol nennen werde, erhalten."'' ----''Translation'': "I was occupied initially with the investigation of the volatile components of excrement in acidic solution. One obtained thereby volatile fatty acids; acetic acid; normal and isobutyric acid; as well as the aromatic substances: phenol, indole and a new substance which is related to indole and which I will name 'skatole'." - Brieger (1878), page 130 ----

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 aromatic ...

in the digestive tract of mammals. Tryptophan is converted to indoleacetic acid, 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 t ...

s to give the methylindole. Skatole can be synthesized via the

Fischer indole synthesis The Fischer indole synthesis is a chemical reaction that produces the aromatic heterocycle indole from a (substituted) phenylhydrazine and an aldehyde or ketone under acidic conditions. The reaction was discovered in 1883 by Emil Fischer. Today ...

. It gives a violet color upon treatment with

potassium ferrocyanide Potassium ferrocyanide 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 chemist Pierr ...

. Skatole, along with the fecal odorant 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 reduce unwanted ambient sounds using active noise control. This is distinct from passive headphones which, if they reduce ambient sounds at all, use techniques such as soundproofing. Noise cancellation makes it possible ...

, 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 attractant

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 Most of the tribe's species ...

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 larvae are coprophagous (dung feeding) although some species have herbivorous or saprophagous larvae. ''Aphodius'' species typically dominate dun ...

''). Skatole has been shown to be an attractant to

gravid In biology and human medicine, gravidity and parity are the number of times a woman is or has been pregnant (gravidity) and carried the pregnancies to a viable gestational age (parity). These terms are usually coupled, sometimes with additional te ...

mosquitoes 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 dilut ...

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 get a mosquito-borne illness each year resulting in over 725,000 deaths. Diseases tra ...

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 ...

Animal studies

Skatole occurs naturally in the feces of all species of mammals and birds, and in the bovine

rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allow ...

. Skatole has been shown to cause

pulmonary edema Pulmonary edema, also known as pulmonary congestion, is excessive edema, liquid accumulation in the parenchyma, tissue and pulmonary alveolus, air spaces (usually alveoli) of the lungs. It leads to impaired gas exchange and may cause hypoxemia an ...

in goats, sheep, rats, and some strains of mice. It appears to selectively target club cells, which are the major site of

cytochrome P450 Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...

enzymes in the lungs. These enzymes convert skatole to a reactive intermediate, 3-methyleneindolenine, which damages cells by forming protein adducts (see

fog fever Fog fever refers to cattle refeeding syndrome which is clinically named acute bovine pulmonary emphysema and edema (ABPEE) and bovine atypical interstitial pneumonia. This veterinary disease in adult cattle follows an abrupt move from feedlot (dri ...

). 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 concent ...

, skatole is regarded as a principal determinant of

boar taint Boar taint is the offensive odor or taste that can be evident during the cooking or eating of pork or pork products derived from non-castrated male pigs once they reach puberty. Boar taint is found in around 20% of entire male finishing pigs. Skato ...

. Skatole contributes to bad breath.

Application

Skatole is the starting material in the synthesis of

atiprosin Atiprosin (developmental code name AY-28,228) is an antihypertensive agent which acts as a selective α1-adrenergic receptor antagonist. It also possesses some antihistamine activity, though it is some 15-fold weaker in this regard than as an ...

References

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

Biosynthesis, chemical synthesis, and reactions

Insect attractant

Animal studies

Application

See also

References