Boc-Aminooxy-PEG4-acid（Cat No.:I015994）is a bifunctional polyethylene glycol derivative with a Boc-protected aminooxy group at one end and a terminal carboxylic acid at the other, linked through a four-unit PEG spacer. The aminooxy group, once deprotected, enables chemoselective oxime or hydrazone ligation with aldehydes and ketones, forming stable conjugates. The carboxyl group allows amide bond formation with amines, expanding its conjugation versatility. The PEG4 backbone enhances solubility, flexibility, and biocompatibility while reducing steric hindrance. This reagent is widely used in peptide chemistry, drug design, and bioconjugation for multifunctional construct development.