Used as a key linker molecule in bioconjugation chemistry, particularly in the synthesis of antibody-drug conjugates (ADCs) and targeted therapeutics. Its structure contains a carboxylic acid group and a protected amine on opposite ends, enabling selective coupling to biomolecules and active payloads. The ethylene glycol-based spacer enhances solubility in aqueous and polar solvents, reduces aggregation, and improves the pharmacokinetic profile of conjugated drugs. Commonly employed in pharmaceutical development to connect cytotoxic agents to monoclonal antibodies via stable or cleavable linkage strategies. Also utilized in PEGylation processes to modify peptides and proteins for improved stability and reduced immunogenicity.