Indole is a compound of pyrrole and benzene in parallel, also known as benzopyrrole. There are two combinations of pyrrole and benzene, called indole and isoindole, respectively. Many derivatives of indole have physiological and pharmacological activities, and can synthesize vasodilators, antihistamines, antipyretic analgesics, etc. in medicine, so indole is also a very important heterocyclic compound.