Used in peptide synthesis as a thiol-containing linker for site-specific conjugation, particularly in the development of antibody-drug conjugates (ADCs) and protein modifications. The Fmoc group allows for solid-phase synthesis compatibility, while the ethyl-SS-propionic acid moiety introduces a cleavable disulfide bond. This enables controlled release of payloads in reducing environments, such as inside cells, making it valuable in targeted drug delivery systems. Also applied in bioconjugation strategies where reversible attachment is needed, leveraging the stability of the disulfide bridge under physiological conditions and its responsiveness to intracellular glutathione.