Used in bioconjugation and pharmaceutical research to introduce polyethylene glycol (PEG) spacers between biomolecules such as peptides, proteins, or drugs and targeting agents. The long PEG chain (12 units) enhances solubility, reduces immunogenicity, and improves the pharmacokinetic profile of conjugated compounds. The t-butyl ester protects the carboxylic acid group during synthesis and can be easily deprotected under mild acidic conditions, allowing for controlled conjugation. The free amino group at the other end enables facile reaction with carboxyl or other reactive groups. Commonly applied in the development of PEGylated therapeutics, diagnostic probes, and drug delivery systems, including antibody-drug conjugates (ADCs), where a hydrophilic linker is needed to optimize biological activity and stability. Suitable for solid-phase synthesis.