Click and Release: How N -Substituted Groups on Hydroxylamine Dictate Click Kinetics and Release Efficiency with Cyclooctynes

Bioorthogonal bond-cleavage chemistry with rapid kinetics in both the click and release steps is essential for optimal performance in complex biological systems. Herein, through screening a focused library of α-nucleophiles, we discovered a new bioorthogonal click-and-release strategy employing N-monoalkyl-substituted hydroxylamines and cyclooctynes. Systematic structural modification of the N-substituent was then carried out to tune the click kinetics. This optimization campaign led to the identification of several analogues that exhibit fast click reaction kinetics (k2 = ∼103 M−1 s−1). However, a consistent trade-off between click kinetics and bond-cleavage efficiency was observed due to regioselectivity issues in the click step, which somewhat limits the broad applicability of this strategy. Future efforts are therefore warranted to address this trade-off and fully unleash its potential for biological applications.