Azido-PEG-t-butyl ester

N₃-PEGn-CH₂COOtBu is a heterobifunctional reagent designed for sequential bioorthogonal conjugation and carboxyl activation, enabling azide-alkyne click chemistry (e.g., CuAAC/SPAAC) followed by acidic deprotection of the tert-butyl ester for further carboxylic acid-mediated modifications. Its key advantages include orthogonal reactivity for controlled stepwise assembly, tunable spacer length (n), and protection of the carboxyl group during click reactions, though the t-Bu ester requires acidic deprotection and the azide group may need protection against reduction.