Used in bioconjugation and pharmaceutical research as a bifunctional linker. The propargyl group enables click chemistry reactions, particularly copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing efficient coupling with azide-containing molecules. The PEG2 spacer improves solubility and provides flexibility, reducing steric hindrance in conjugates. The tert-butyl ester (tBu) group protects a carboxylic acid functionality, which can be deprotected under mild acidic conditions to release a free carboxylic acid for further coupling. Commonly employed in the synthesis of peptide-drug conjugates, antibody-drug linkers, and functionalized surfaces for assays or materials science. Its design supports controlled, stepwise assembly of complex molecular architectures.