t-Boc-Aminooxy-PEG4-NHS ester（Cat No.:I015993）is a heterobifunctional linker featuring a Boc-protected aminooxy group on one end and an NHS ester on the other, connected through a four-unit PEG spacer. The Boc group provides temporary protection of the aminooxy functionality, enabling selective deprotection for oxime or hydrazone ligation with aldehydes and ketones. The NHS ester reacts efficiently with primary amines to form stable amide bonds. The PEG4 spacer enhances solubility, flexibility, and reduces steric hindrance. This reagent is widely applied in bioconjugation, peptide synthesis, and drug development for multifunctional biomolecule construction.