Aminooxy-PEG-acid（Acid-PEG-Aminooxy) is a chemical compound that belongs to the family of polyethylene glycol (PEG) derivatives. It contains two functional groups – an aminooxy group and a carboxylic acid group, which make it a versatile tool for various applications in pharmaceutical research and development. The aminooxy group allows for selective conjugation to aldehydes and ketones, while the carboxylic acid group can be used for further modifications. Aminooxy-PEG-acid can be used as a linker to attach small molecules, peptides, or proteins to a drug carrier system, thus enhancing their solubility, stability, and pharmacokinetics. Additionally, this compound can be used for bioconjugation and labeling of biomolecules, making it a valuable tool in drug discovery and development.