Abstract :
Recent developments in bond cleavage reactions have expanded the scope of bioorthogonal chemistry beyond click ligation and enabled new strategies for probe activation and therapeutic delivery. Investigating the mechanistic features of the reaction's performance, profound pH sensitivity, is discovered, and exploited it with acid-functionalized tetrazines that both enhance and markedly accelerate release, and ultimately uncovered an unexpected dead-end isomer as the reason for poor release. Implementing facile methods to prevent formation of this dead end, exceptional efficiency, with essentially complete release across the full scope of physiologic pH, potentiating drug-delivery strategies and expanding the dynamic range of bioorthogonal on/off control, are achieved.