S-Carboxyethylisothiuronium Chloride is primarily used in organic synthesis as a reagent for the modification of proteins and peptides. It plays a significant role in the carboxyethylation process, which is essential for introducing specific functional groups into biomolecules. This chemical is also utilized in the preparation of derivatives that are important in biochemical research, particularly in studies involving enzyme activity and protein interactions. Additionally, it finds application in the development of pharmaceuticals, where it aids in the synthesis of compounds with potential therapeutic effects. Its ability to act as a cross-linking agent makes it valuable in the production of polymers and materials with tailored properties for industrial applications.