Used in antibody-drug conjugate (ADC) development as a linker-payload component. The azido group enables bioorthogonal conjugation via click chemistry, allowing selective attachment to antibodies. PEG5 spacer enhances solubility and reduces aggregation. The Ala-Ala-Asn tripeptide is a cathepsin B-cleavable sequence, enabling intracellular drug release in tumor cells. PAB (para-aminobenzyl alcohol) acts as a self-immolative spacer, facilitating efficient release of active payloads upon peptide cleavage. Commonly employed in targeted cancer therapies to deliver cytotoxic agents selectively to tumor cells while minimizing systemic toxicity.