Used in bioconjugation processes, particularly in the synthesis of antibody-drug conjugates (ADCs). Its structure enables selective linking of cytotoxic agents to monoclonal antibodies, allowing targeted delivery to cancer cells. The maleimide group (from the dihydro-1H-pyrrol-1-yl moiety) reacts specifically with thiol groups on reduced antibodies, forming a stable thioether bond. The polyethylene glycol (PEG) spacer improves solubility and reduces aggregation, enhancing the pharmacokinetic profile of the conjugate. The carboxylic acid terminus allows further activation for amide bond formation with amine-containing drugs or linkers. Commonly applied in pharmaceutical development for oncology therapeutics where controlled drug release and high conjugation efficiency are critical.