Used in bioconjugation reactions, particularly in click chemistry applications. The propargyl group enables copper-catalyzed azide-alkyne cycloaddition (CuAAC), allowing efficient labeling or attachment to azide-containing molecules. The aminooxy group facilitates stable oxime bond formation with carbonyl groups (aldehydes or ketones) found in glycans or oxidized biomolecules. The PEG4 spacer enhances water solubility, reduces aggregation, and improves the accessibility of reactive groups, making it ideal for use in probe development, protein modification, and surface functionalization in biological systems.