What is Indole?
Indole, also known as benzopyrrole, is a heterocyclic organic compound. Indole is present in various types of flower oils like jasmine and orange blossom. Moreover, it is also a key component in coal tar and faecal matter. Indole is primarily used in tryptophan, an important amino acid. It is also an important constituent of indoleacetic acid. Indoleacetic acid is an essential hormone that promotes the formation of roots in plants. First isolated in 1866, Indole is commonly derived from phenylhydrazine. Indole is also abundantly present in pyruvic acid.
Apart from tryptophan, various compounds obtainable from animal or plant sources contain the molecular Indole structure. The popularly known group of compounds are the Indole alkaloids. Indole is a colourless solid that is has a rich aroma. The Indole structure also depicts that it has high solubility. Several bioactive aromatic compounds containing the Indole molecules have biological and chemical applications. To be precise, Indole is abundantly present in a wide variety of synthetic drugs. The Indole structure depicts a tendency to bind to various types of receptors.
Indole Compounds
To know about Indole compounds, you should have proper knowledge of their structure. Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure that contains six-membered benzene rings connected to a five-membered pyrrole ring. Indole is broadly available in the natural environment and can be developed by a large number of bacteria. What’s more, Indole is a key component of intracellular signal molecules. This is the reason that it can monitor and regulate several aspects of bacterial physiology, which includes the formation of spores. Tryptophan, an essential amino acid, is derived from Indole. Indole also aids with the formation of the neurotransmitter serotonin. The Indole compounds thus play an important role in the proper functioning of the human body.
The Indole test conducted by researchers has depicted that Indole can be promising against defending humans from malaria, diabetes, tuberculosis, hypertension, etc. The Indole test has also shown that Indole possesses a plethora of biological activities. For instance, with the Indole test, researchers have been able to find the efficacy of Indole against cancers, HIV, and other terminal illnesses. Indole is also a potent antioxidant and thus decreases oxidative stress in the human body.
All these promising aspects of Indole have stirred a great amount of interest among the researchers. Researchers are exploring various ways to include Indole in life-saving drugs as it is highly effective against serious illnesses.
(Image will be uploaded soon)
Things to Know About Fischer Indole Synthesis
It is imperative to know about the Fischer Indole Synthesis to know more about its chemical and biological properties. As stated above, Indole has strong potential against various types of diseases.
The arylhydrazone developed from the condensation of aryl hydrazine and carbonyl compound usually undergoes protonation and isomerization to the enamine lautomer. In the next process, the protonated enamine lautomer experiences irreversible electrocyclic rearrangement in the form of (3,3). In this process, the N-N bond is broken.
The Fischer Indole Synthesis refers to a chemical reaction that develops the aromatic heterocyclic Indole from aldehyde or ketone under acidic mediums. This reaction was first introduced by Emil Fischer in 1883. That’s why the reaction is known as Fischer Indole Synthesis. Quite impressively, the antimigraine drugs of the triptan variety are usually synthesised with the help of this method.
Indole Acetic Acid Properties
To be precise, it is the most commonly occurring plant hormone. It belongs to the auxin class of plant hormones. From the perspective of plant biologists, Indole Acetic Acid has been a topic of constant research and is highly soluble in polar organic compounds. This acid is usually developed in cells of the bud and young leaves. Plants are able to synthesize this form of acid with the help of various biosynthetic pathways. Researchers have conducted extensive trials in the lab with this acetic acid. In rats, it is a product of both colonic and endogenous microbial metabolism.
Indole is gaining increasing prominence among various types of researchers. Indole actively takes part in cell elongation and helps in the production of essential amino acid tryptophan. In the future, Indole is anticipated to play an important role in the manufacturing of various types of drugs.
FAQs on Indole
1. What is indole and what is its chemical structure?
Indole is a bicyclic, aromatic heterocyclic organic compound. Its structure consists of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. The chemical formula for indole is C₈H₇N. Because it is a fusion of a benzene and pyrrole ring, it is also known by the name benzopyrrole. You can learn more about such structures in this article on Heterocyclic Compounds.
2. What are some important uses and functions of the indole ring system?
The indole ring system is a vital structural motif found in many significant biological molecules and synthetic compounds. Its major uses and functions include:
- Amino Acids: It forms the core side chain of the essential amino acid tryptophan.
- Plant Hormones: Indole derivatives such as Indole-3-acetic acid (IAA) and Indole-butyric acid (IBA) are crucial auxins that regulate plant growth and development.
- Pharmaceuticals: The indole structure is a key component in many drugs, including anti-inflammatory agents, anti-migraine drugs (triptans), and anti-cancer treatments.
- Perfumery: Despite its unpleasant smell at high concentrations, it imparts a floral scent at very low concentrations and is used as a fixative in perfumes.
3. Is indole considered an amino acid?
No, indole itself is not an amino acid. This is a common point of confusion. Indole is a distinct chemical compound, while amino acids are molecules containing both an amine (-NH₂) and a carboxyl (-COOH) functional group. The confusion arises because the essential amino acid tryptophan contains an indole ring as its side group. In the body and in certain microorganisms, tryptophan can be metabolised to produce indole.
4. Why is indole classified as an aromatic compound?
Indole is classified as an aromatic compound because it fulfils Hückel's rule for aromaticity. Its bicyclic system contains a total of 10 π (pi) electrons, which is a valid Hückel number (4n+2, where n=2). These electrons are completely delocalised across both the benzene and pyrrole rings, forming a stable, planar structure. The lone pair of electrons on the nitrogen atom actively participates in this delocalised system, contributing to its aromatic character.
5. What is a common laboratory method for indole synthesis?
One of the most renowned and versatile methods for synthesising indoles in a laboratory is the Fischer Indole Synthesis. This reaction involves the treatment of a phenylhydrazine with an aldehyde or a ketone under acidic conditions, which then undergoes heating. The reaction proceeds through a key step known as a [3,3]-sigmatropic rearrangement to form the indole ring structure. You can read more about this specific reaction in the article on Fischer Indole Synthesis.
6. What does indole smell like, and why is it used in perfumes?
The scent of indole is highly dependent on its concentration. At high concentrations, indole has a very strong, pungent, and often described as fecal odour. However, when it is highly diluted, its scent profile completely changes to a pleasant, rich floral note, similar to jasmine and orange blossoms. This unique dual character allows it to be used in very small quantities in perfumery to add complexity, richness, and a long-lasting base to floral fragrances.
7. What is the indole test used for in microbiology?
The indole test is a qualitative biochemical test used to determine a microorganism's ability to break down the amino acid tryptophan to produce indole. This test is a critical diagnostic tool in microbiology for differentiating bacterial species, especially within the Enterobacteriaceae family. The production of indole is detected by adding Kovac's reagent; a positive result is indicated by the formation of a cherry-red layer at the top of the broth, confirming the presence of the enzyme tryptophanase.
