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.
Etrasimod is a new generation of oral S1P receptor modulator, which can specifically bind to S1P receptors 1, 4, and 5. It is being studied for a range of immune inflammatory diseases, including ulcerative colitis, Crohn's disease, atopic dermatitis, eosinophilic esophagitis and alopecia areata. At present, the highest stage of research and development of the drug is to apply for marketing, which is used to treat ulcerative colitis and is expected to be approved by FDA in this month.