indol

Indole, also called indol in older literature, is an aromatic heterocyclic organic compound with the formula C8H7N. It comprises a benzene ring fused to a five-membered ring containing a single nitrogen atom (a pyrrole). The structure gives the indole nucleus, a common scaffold in natural products. Indole is the parent compound of the broad class known as indoles, and many derivatives are widespread in chemistry and biology.

Indole occurs in nature and is produced by various organisms. It has been found in coal tar and is formed in biological systems from the amino acid tryptophan. In plants, indole serves as a precursor to important metabolites, including the plant hormone indole-3-acetic acid (IAA) and a range of alkaloids. The indole ring also appears in biomolecules such as tryptophan, serotonin, and melatonin.

Indole and its derivatives are valued in organic synthesis and industry. The indole scaffold is a key motif in pharmaceuticals, agrochemicals, dyes, and fragrances. A classical method to synthesize indole is the Fischer indole synthesis, which couples phenylhydrazines with carbonyl compounds. Indole is also a core structure in many natural products and synthetic compounds used in research and medicine.

Physically, indole is a colorless to pale yellow solid that is insoluble in water but soluble in many organic solvents. It has a distinct, mildly floral odor and shows UV fluorescence. Safety considerations include irritation on contact; it should be handled with appropriate precautions in laboratory settings.