Used in bioconjugation for linking biomolecules with improved solubility and reduced aggregation. The PEG4 spacer enhances hydrophilicity, allowing better compatibility in aqueous biological systems. The chloroacetamido group reacts selectively with thiol groups (e.g., cysteine residues) to form stable thioether bonds, enabling site-specific protein or peptide modification. The Boc-protected amine allows for controlled deprotection and further coupling steps in multi-step synthesis, making it valuable in developing antibody-drug conjugates (ADCs), targeted therapies, and functionalized probes for diagnostics.