Used as a linker in antibody-drug conjugates (ADCs), particularly in the development of targeted cancer therapies. The Fmoc-D-Val-D-Cit-PAB structure incorporates a para-aminobenzyloxycarbonyl (PAB) group, which acts as a self-immolative spacer. After the ADC is internalized by target cells and degraded in lysosomes, the PAB linker enables the release of active cytotoxic drugs, such as maytansinoids or doxorubicin derivatives. The D-Val-D-Cit dipeptide segment enhances stability in circulation and is selectively cleaved by lysosomal enzymes like cathepsin B. The Fmoc group can serve as a protective moiety during synthesis and may aid in purification. This linker system improves the therapeutic index of ADCs by minimizing premature drug release and enhancing tumor-specific drug delivery.