Pyrrolidine, also known as tetrahydropyrrole, is a saturated five-membered heterocyclic ring, which is miscible with water. Pyrrolidine exists in many alkaloids and drug molecules, such as kappa opioids, antagonists of dopamine D4 receptors, and HIV reverse transcriptase inhibitors.
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.