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.
Thiazolines are a group of isomeric five-membered heterocyclic compounds containing both sulfur and nitrogen. Thiazoline exists in three isomeric forms namely 2-thiazoline, 3-thiazoline and 4-thiazoline. Oxazolines, oxazoles, thiazolines, and thiazoles form the characteristic heterocyclic building blocks of lissoclinum peptide alkaloids.