Phthalimide: a potential warhead for switchable and bioorthogonal conjugation

Abstract

4-Azidophthalimide, previously reported as a photoaffinity labeling (PAL) tag, was repurposed as a post-conjugation warhead. Using the phthalimide–amine reaction, cyanine amines were successfully conjugated to target proteins after PAL and later replaced with other amines, demonstrating its “switchable” nature. These findings highlight phthalimide's unique characteristics as a novel chemical tool for bioorthogonal conjugations.