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.
Oxirane is a three-membered ring compound consisting of one oxygen atom and two carbon atoms. Oxirane is present in natural products such as cryptocin, which has anticancer properties, and azidomycin, trienone, and epoxidomycin, which have shown activity against drug-resistant leukemias and AIDS-related lymphomas. Other oxirane containing bioactive molecules have anti-inflammatory, immunosuppressive, and antitumor activities. Oxiranes are a strained ring susceptible to various nucleophilic, ring-opening or rearrangement reactions, so they are considered to be one of the most important intermediates in organic synthesis.
Pyrrolines, also called dihydropyrroles, are obtained from aromatic pyrroles by hydrogenation. 1-pyrroline is a cyclic imine, while 2-pyrroline and 3-pyrroline are cyclic amines.