Procysteine

Procysteine is an organic compound with the formula CH₂NHC(O)SCHCO₂H. It is a colorless solid. The compound is classified as a derivative of the heterocycle 2-oxo-1,3-thiazoline. Such rings are prepared by the action of phosgene (or related dehydration reagents on 2-aminoethanethiols, in this case cysteine:

HSCH₂CH(NH₂)CO₂H + COCl₂ → CH₂NHC(O)SCHCO₂H + 2 HCl

The compound hydrolyzes to cysteine. The hydrolysis is catalyzed by 5-oxoprolinase.