In this work, we synthesized various iminiumthiolactone derivatives (ITL) that exhibit both higher reactivity and water-solubility than their thiolactone predecessors. We envisioned that these improved properties would facilitate the coupling of biological substrates. ITLs are structurally based on the Traut's reagent also known as 2-iminothiolane where the carbonyl oxygen of thiolactones is replaced by NH, thus, representing an imine. With this small alteration comes a large increase in reactivity towards primary amines at pH = 7-9. In this pH range, the Traut's reagent exists in its protonated form as an iminiumthiolactone (ITL), which further enhances its water solubility. Since its invention in 1973, the Traut's reagent has been continuously used to modify biological molecules (e.g., proteins, enzymes, ribosomes) and anchor them to surfaces, tags, or other (bio)macromolecules. Despite its consistent record of use, ITLs with substitutions on the heterocycle have only been reported twice by Carroll and coworkers. In the respective publications, the authors investigate the impact of various alkyl-and phenyl-sustitutions on the reactivity and stability of the ITL derivatives. Nonetheless, the commercially available Traut's reagent only exists as non-substituted five-membered heterocycle, severely limiting its potential as ligation method.