Benzyl-PEG-azide is a functionalized compound that contains three important functional groups: a benzyl group, a polyethylene glycol (PEG) spacer, and an azide group. This molecule has attracted a lot of interest in pharmaceutical research and development due to its ability to modify and functionalize various biomolecules, including peptides, proteins, and nucleic acids. The benzyl group provides hydrophobic interactions with biological membranes and other hydrophobic domains, while the PEG spacer imparts water solubility and reduces immunogenicity. The azide group can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction with alkyne-modified biomolecules, enabling site-specific conjugation and labeling. This versatile compound has a wide range of potential applications in drug delivery, diagnostics, and therapeutics, making it an important tool in modern pharmaceutical research and development.