Used in bioorthogonal chemistry for site-specific bioconjugation, particularly in live cell labeling and protein modification. Its strained alkyne group enables rapid, catalyst-free click reactions with tetrazine derivatives, allowing efficient tagging of biomolecules in complex biological environments. The PEG4 spacer enhances water solubility and reduces nonspecific binding, improving signal-to-noise ratios in imaging applications. The t-butyl ester acts as a protected carboxylic acid, which can be deprotected under mild acidic conditions to enable further functionalization. Commonly employed in the development of antibody-drug conjugates, targeted probes, and multifunctional ligands for diagnostic and therapeutic applications.