Used in bioconjugation processes, particularly in the preparation of antibody-drug conjugates (ADCs) and other targeted therapeutics. Its structure contains a maleimide group that selectively reacts with thiol groups (–SH) on cysteine residues of proteins, enabling stable linkage between biomolecules and functional payloads. The long, hydrophilic polyethylene glycol (PEG) spacer improves solubility, reduces aggregation, and enhances the pharmacokinetic properties of the conjugated molecules. The terminal carboxylic acid allows for further activation and coupling to amines, making it useful for multi-step conjugation strategies. Commonly employed in pharmaceutical research and development for creating highly specific, effective biopharmaceuticals.