Used in bioconjugation reactions, particularly in click chemistry applications. Its alkyne group reacts efficiently with azides via copper-catalyzed azide-alkyne cycloaddition (CuAAC), enabling site-specific labeling of biomolecules such as peptides, proteins, and antibodies. The PEG4 spacer enhances solubility in aqueous systems and reduces non-specific binding, improving the bioavailability and stability of conjugated products. The acetylthio group allows for reversible attachment to thiol-reactive sites, making it useful in the development of cleavable linkers for drug delivery systems and targeted therapeutics. Commonly employed in the synthesis of antibody-drug conjugates (ADCs) and diagnostic probes.