Heterocyclic compound where benzene is fused with pyrrole ring. It was first identified by Baeyer in 1866 while doing research on the structure of natural dye indigo. Indole pharmacophore is a ubiquitous constituent of many natural products which includes plant hormones (indole-3-acetic acid), some animal hormones such as melatonin and serotonin and many alkaloids that includes vinblastine, vincristine, vindesine, vinorelbine, ajmaline and physostigmine. Similarly it is main component of several synthetic drugs such as indomethacin, fluvastatin, zafirlukast and ondansetron.