Used in bioconjugation and pharmaceutical research as a bifunctional linker, particularly in the development of antibody-drug conjugates (ADCs) and peptide modifications. The N3 group enables copper-catalyzed or strain-promoted azide-alkyne cycloaddition (click chemistry), allowing efficient and selective coupling with alkyne-functionalized biomolecules. The PEG6 spacer enhances solubility in aqueous and organic solvents, reduces aggregation, and improves bioavailability by increasing the hydrodynamic radius of conjugated molecules. The terminal t-butyl ester (COOtBu) acts as a protected carboxylic acid, which can be deprotected under mild acidic conditions to yield a free carboxylic acid for further amide bond formation or coupling to amines. This structure is valuable in constructing drug delivery systems, diagnostic probes, and multifunctional ligands where controlled spacing, solubility, and sequential conjugation are required.