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.
Pyrazolidine is a saturated organic heteromonocyclic parent. Pyrazolidines are important synthetic intermediates in organic synthesis. Pyrazolidine compounds are valuable heterocyclic compounds due to their powerful biological properties.