# Skatole

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.
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. Its name derives from the Greek root skato-, meaning feces. Skatole was discovered in 1877 by the German physician Ludwig Brieger (1849–1919).
   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.
   [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 indole-derived substance which I will name "skatole".]

## 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. 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.
It gives a violet color upon treatment with potassium ferrocyanide.
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.

## 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. It is also known for being an attractant for the Tasmanian grass grub beetle (Aphodius tasmaniae).
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.
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.

## Animal studies

Skatole occurs naturally in the feces of all species of mammals and birds, and in the bovine rumen.
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).
With the testicular steroid androstenone, 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.

## Application

Skatole is the starting material in the synthesis of atiprosin.