Used in bioconjugation processes to introduce a cleavable linker between biomolecules such as proteins, peptides, or antibodies and functional groups like amines. The NHS ester reacts efficiently with primary amines to form stable amide bonds, enabling labeling or immobilization. The PEG4 spacer enhances solubility in aqueous systems and reduces steric hindrance, improving reaction efficiency. The NHPI (N-hydroxyphthalimide) group allows for mild cleavage under reducing conditions, making it useful in drug delivery systems or reversible crosslinking applications where controlled release is required. Commonly applied in the development of antibody-drug conjugates (ADCs), diagnostic probes, and targeted therapeutics.