Used in the synthesis of antibody-drug conjugates (ADCs), this compound serves as a linker that connects the antibody to a cytotoxic drug. The Fmoc-Val-Cit-PAB-OH contains a cleavable peptide sequence (Val-Cit) and a self-immolative spacer (PAB), which are critical for targeted drug release inside cancer cells. Upon internalization of the ADC into tumor cells, the Val-Cit dipeptide is selectively cleaved by lysosomal enzymes, particularly cathepsin B. This cleavage triggers the release of the active drug from the PAB spacer, enabling precise delivery and minimizing damage to healthy tissues. The Fmoc group allows for controlled stepwise solid-phase peptide synthesis, making it valuable in constructing complex ADC architectures. Its design enhances plasma stability while ensuring efficient intracellular activation, contributing to improved therapeutic efficacy and safety in cancer treatments.