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.
Oxazolidines are five-membered ring compounds consisting of three carbons, nitrogen and oxygen. Oxygen and nitrogen are in the 1 and 3 positions, respectively. Oxazolidine is in general yellow or slightly yellow, alkaline liquid or solid, easily hydrolyzed by water or alcohol. It is insoluble in water (or hydrolyzed); soluble in benzene and chloroform. Oxazolidine derivatives are five-membered cyclic compounds containing at least one oxygen and nitrogen in their molecular structure. Oxazolidine derivatives are known to possess various therapeutic activities, such as anticancer and antibiotic properties.