Azido-PEG-nitrile is a versatile compound that contains three functional groups: an azido group, a polyethylene glycol (PEG) linker, and a nitrile group. This compound has found widespread use in pharmaceutical research and development due to its ability to selectively modify biomolecules such as peptides, proteins, and nucleic acids. The azido group allows for bioorthogonal chemistry reactions, which can be used to label and track biomolecules in living cells or organisms without disrupting their function. The PEG linker can improve the solubility, stability, and pharmacokinetics of the modified biomolecules. The nitrile group can be used as a site for further functionalization or as a bioisostere for other functional groups.