The name indole is derived from the Indian word indigo, the blue dye that was first exported to Europe from India  in the 16th century. It is constituted by fusion of the benzene ring with 2,3-positions of pyrrole and has properties of  both rings. Indole being a π-rich heterocycle has the characteristic of light-induced autoxidation and thus it is procured away from light and oxygen.

Biologically active

Indole is the most biologically active, abundantly distributed heterocycle in nature as a sub-structure in complexindole alkaloids. The natural amino acid tryptophan is present in various pharmacologically active peptides, proteins, and various drugs. The indole ring features various natural products, such as serotonin, a very important  neurotransmitter having several physiological functions in the body, and melatonin, responsible for the regulation  of sleep/wake. The other class of compounds containing the indole ring are plant growth regulators such as indole  3-acetic acid and synthetic indole 3-butyric acid. The indole structure is also present in structurally complex alkaloids  such as lysergic acid diethyl amide, reserpine, and strychnine.

Uses

In contrast, several synthetic drugs currently in clinical use contain the indole nucleus, including sumatryptan, a  synthetic tryptamine used in the treatment of migraine, and the nonsteroidal antiinflammatory drugs indomethacin  and etodolac.

Synthesis 

Reissert Synthesis83 A condensation of o-nitrotoluene with diethyl oxalate in the presence of organic base, NaOMe, gave ethyl  o-nitrophenylpyruvate, which after reductive cyclization in the presence of Zn/AcOH or by hydrogenation in acetic  acid over Pt as catalyst afforded indole.