Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring.
Indole is a common component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an indole ring are called indoles. The amino acid tryptophan is an indole derivative and the precursor of the neurotransmitter serotonin
Indole undergoes electrophilic substitution, mainly at position 3. Substituted indoles are structural elements of (and for some compounds the synthetic precursors for) the tryptophan-derived tryptamine alkaloids like the neurotransmitter serotonin and melatonin.