Endo-BCN-PEG-acid is a molecule that belongs to the class of bioconjugation reagents. It is a bifunctional compound that contains an endocyclic strained alkene, PEG linker, and a carboxylic acid group. The endocyclic strained alkene allows for a fast and selective reaction with a variety of functional groups, such as amines, thiols, and alkenes, to form stable covalent bonds. The PEG linker, on the other hand, enhances the solubility and bioavailability of the molecule in aqueous environments. The carboxylic acid group confers an acidic pH, which is useful in drug delivery applications. Endo-BCN-PEG-acid has been widely used in pharmaceutical research and development as a tool for drug conjugation and targeted delivery.