Used in bioconjugation to link drugs, proteins, or peptides with targeting molecules while improving solubility and stability. The Boc group allows controlled deprotection for stepwise synthesis, enabling precise attachment in peptide and protein modifications. PEG spacer reduces aggregation and extends circulation time in therapeutic applications. Carboxylic acid end enables coupling to amines via EDC/NHS chemistry, useful in creating antibody-drug conjugates (ADCs) and functionalizing nanoparticles. Commonly applied in drug delivery systems, diagnostics, and surface modification of medical devices.