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.
Thiomorpholine is a nitrogen- and sulfur-containing heterocyclic compound with the molecular formula C4H9NS. It can be considered a thio analog of morpholine. Thiomorpholines are comparable to other secondary amines in terms of nucleophilicity and N-alkylation or acylation with alkyl groups or acid halides.