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Skatole
Names
	Preferred IUPAC name 3-Methyl-1H-indole
	Other names 3-Methylindole; 4-Methyl-2,3-benzopyrrole
Identifiers
CAS Number	83-34-1 ;
3D model (JSmol)	Interactive image; Interactive image;
ChEBI	CHEBI:9171 ;
ChemSpider	6480 ;
ECHA InfoCard	100.001.338
PubChem CID	6736;
UNII	9W945B5H7R ;
CompTox Dashboard (EPA)	DTXSID8021775 ;
	InChI InChI=1S/C9H9N/c1-7-6-10-9-5-3-2-4-8(7)9/h2-6,10H,1H3 Key: ZFRKQXVRDFCRJG-UHFFFAOYSA-N ; InChI=1/C9H9N/c1-7-6-10-9-5-3-2-4-8(7)9/h2-6,10H,1H3 Key: ZFRKQXVRDFCRJG-UHFFFAOYAZ;
	SMILES Cc1c[nH]c2ccccc12; c1cccc2c1c(c[nH]2)C;
Properties
Chemical formula	C9H9N
Molar mass	131.178 g·mol−1
Appearance	White crystalline solid
Odor	Fecal matter (pleasant flowery aroma in low concentrations)
Melting point	93 to 95 °C (199 to 203 °F; 366 to 368 K)
Boiling point	265 °C (509 °F; 538 K)
Solubility in water	Insoluble
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Skatole or 3-methylindole is an organic compound belonging to the indole family. It occurs naturally in the feces of mammals and birds and is the primary contributor to fecal odor. In low concentrations, it has a flowery smell and is found in several flowers and essential oils, including those of orange blossoms, jasmine, and Ziziphus mauritiana. It has also been identified in certain cannabis varieties.^[1]

It is used as a fragrance and fixative in many perfumes and as an aroma compound. It is also used in low concentrations in some ice cream as a flavor enhancer.^[2] Its name derives from the Greek root skato-, meaning feces. Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919).^[3]^[4]^[5]

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 in the digestive tract of mammals. Tryptophan is converted to indoleacetic acid, which decarboxylates to give the methylindole.^[6]^[7] Once it is created in the digestive tract of mammals, it is metabolized by cytochrome P450 enzymes in the liver.^[8]

Skatole can be synthesized via the Fischer indole synthesis.^[9]

It gives a violet color upon treatment with potassium ferrocyanide.^{[citation needed]}

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, 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.^[10]

Insect studies

Skatole is one of many compounds that are attractive to males of various species of orchid bees, which apparently gather the chemical to synthesize pheromones; it is commonly used as bait for these bees for study.^[11] It is also known for being an attractant for the Tasmanian grass grub beetle (Aphodius tasmaniae).^[12]

Skatole has been shown to be an attractant to gravid mosquitoes in both field and laboratory conditions. Because this compound is present in feces, it is found in combined sewage overflows (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 diseases such as West Nile virus.^[13]

The release of skatole by certain parasitic wasps in the family Bethylidae 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.^[14]

Animal studies

Skatole occurs naturally in the feces of all species of mammals and birds, and in the bovine rumen.^[15]

Skatole has been shown to cause pulmonary edema in goats, sheep, rats, and some strains of mice. It appears to selectively target club cells, which are the major site of cytochrome P450 enzymes in the lungs. These enzymes convert skatole to a reactive intermediate, 3-methyleneindolenine, which damages cells by forming protein adducts (see fog fever).^[16]

With the testicular steroid androstenone, skatole is regarded as a principal determinant of boar taint.^[17] 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.^[18] 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%.^[8]

Skatole contributes to bad breath.^[19]

Application

Skatole is the starting material in the synthesis of atiprosin.

References

^ Oswald, Iain W. H.; Paryani, Twinkle R.; Sosa, Manuel E.; Ojeda, Marcos A.; Altenbernd, Mark R.; Grandy, Jonathan J.; Shafer, Nathan S.; Ngo, Kim; Peat, Jack R.; Melshenker, Bradley G.; Skelly, Ian; Koby, Kevin A.; Page, Michael F. Z.; Martin, Thomas J. (2023-10-12). "Minor, Nonterpenoid Volatile Compounds Drive the Aroma Differences of Exotic Cannabis". ACS Omega. 8 (42): 39203–39216. doi:10.1021/acsomega.3c04496. ISSN 2470-1343. PMC 10601067. PMID 37901519.
^ "The Chemistry of Ice Cream – Components, Structure, & Flavour". Compound Interest. 2015-07-14. Retrieved 2024-11-19.
^ Brieger, Ludwig (1877). "Über die flüchtigen Bestandtheile der menschlichen Excremente" [On the volatile components of human excrement]. Berichte der Deutschen Chemischen Gesellschaft. 10: 1027–1032. doi:10.1002/cber.187701001288. Retrieved 3 November 2020.
^ Brieger, Ludwig (1878). "Über die flüchtigen Bestandtheile der menschlichen Excremente". Journal für Praktische Chemie. 17: 124–138. doi:10.1002/prac.18780170111. Retrieved 3 November 2020. Das Skatol ... (von το σχατος = faeces) ... (Skatole ... (from το σχατος = feces....)
^ Brieger, Ludwig (1879). "Über Skatol" [On skatole]. Berichte der Deutschen Chemischen Gesellschaft. 12 (2): 1985–1988. doi:10.1002/cber.187901202206. Retrieved 3 November 2020.
^ Whitehead, T. R.; Price, N. P.; Drake, H. L.; Cotta, M. A. (25 January 2008). "Catabolic pathway for the production of skatole and indoleacetic acid by the acetogen Clostridium drakei, Clostridium scatologenes, and swine manure". Applied and Environmental Microbiology. 74 (6): 1950–3. Bibcode:2008ApEnM..74.1950W. doi:10.1128/AEM.02458-07. PMC 2268313. PMID 18223109.
^ Yokoyama, M. T.; Carlson, J. R. (1979). "Microbial metabolites of tryptophan in the intestinal tract with special reference to skatole". The American Journal of Clinical Nutrition. 32 (1): 173–178. doi:10.1093/ajcn/32.1.173. PMID 367144.
^ ^a ^b Bilić-Šobot, Diana; Zamaratskaia, Galia; Rasmussen, Martin Krøyer; Čandek-Potokar, Marjeta; Škrlep, Martin; Povše, Maja Prevolnik; Škorjanc, Dejan (2016-10-20). "Chestnut wood extract in boar diet reduces intestinal skatole production, a boar taint compound". Agronomy for Sustainable Development. 36 62. Germany: Springer Science+Business Media. doi:10.1007/s13593-016-0399-1. ISSN 1773-0155. OCLC 8092619612.
^ Emil Fischer (1886) "Indole aus Phenylhydrazin" (Indole from phenylhydrazine), Annalen der Chemie, vol. 236, pages 126-151; for Fischer's synthesis of skatole, see page 137. (Fischer was not the first to prepare skatole. It was prepared, via other methods, in 1880 by von Baeyer, and in 1883 by Otto Fischer and German and by Fileti.)
^ Holusha, John (15 July 1990). "Technology; Making Bad Smell Good by Tricking the Nose". The New York Times.
^ Schiestl, F.P. & Roubik, D.W. (2004). "Odor Compound Detection in Male Euglossine Bees". Journal of Chemical Ecology. 29 (1): 253–257. doi:10.1023/A:1021932131526. hdl:20.500.11850/57276. PMID 12647866. S2CID 2845587.
^ Osborne, G. O.; Penman, D. R.; Chapman, R. B. (1975). "Attraction of Aphodius tasmaniae Hope to skatole". Australian Journal of Agricultural Research. 26 (5): 839–841. doi:10.1071/AR9750839.
^ Beehler, J W; Millar, J G; Mullah, M S (1994). "Field evaluation of synthetic compounds mediating oviposition in Culex mosquitoes (Diptera: Culicidae)". Journal of Chemical Ecology. 20. Germany: Springer Science+Business Media: 281–291. Bibcode:1994JCEco..20..281B. doi:10.1007/BF02064436. OCLC 5655055511. PMID 24242053. S2CID 23784247.
^ MARLÈNE GOUBAULT, TIM P. BATCHELOR, ROBERTO ROMANI, ROBERT S. T. LINFORTH, MATTHIAS FRITZSCHE, WITTKO FRANCKE, IAN C. W. HARDY, Volatile chemical release by bethylid wasps: identity, phylogeny, anatomy and behaviour, Biological Journal of the Linnean Society, Volume 94, Issue 4, August 2008, Pages 837–852, https://doi.org/10.1111/j.1095-8312.2008.01022.x
^ Yokoyama, M. T.; Carlson, J. R.; Holdeman, L. V. (1977). "Isolation and characteristics of a skatole-producing Lactobacillus sp. from the bovine rumen". Applied and Environmental Microbiology. 34 (6): 837–842. Bibcode:1977ApEnM..34..837Y. doi:10.1128/AEM.34.6.837-842.1977. PMC 242757. PMID 563703.
^ Miller, M; Kottler, S; Ramos-Vara, J; Johnson, P; Ganjam, V; Evans, T (2003). "3-Methylindole Induces Transient Olfactory Mucosal Injury in Ponies". Veterinary Pathology. 40 (4): 363–70. doi:10.1354/vp.40-4-363. PMID 12824507.
^ Wesoly, R.; Weiler, U. (2012). "Nutritional Influences on Skatole Formation and Skatole Metabolism in the Pig". Animals. 2 (2): 221–242. doi:10.3390/ani2020221. PMC 4494329. PMID 26486918.
^ Moki, R.; Sakamoto, E.; Yamaguchi, T. Method For Reducing Skatole And/or Indole In Animals. United States Patent 10792352. Jun 10, 202.
^ Franklin, Deborah (1 May 2013). "To Beat Bad Breath, Keep the Bacteria in Your Mouth Happy". Scientific American. 308 (5): 30, 32. doi:10.1038/scientificamerican0513-30. PMID 23627212. Retrieved 3 November 2020.