Figure 2.

State-of-the-art bioorthogonal cleavage reactions. BCRs can be classified as transition-metal-triggered cleavage reactions (entries 1–11), cycloaddition-mediated cleavage reactions (entries 12–25 and 31), and redox-based cleavage reactions (entries 26–30), all of which have found an array of exciting applications with excellent biocompatibility both in vitro and in living cells or animals. Reported pseudo-second-order constants (k₂) are listed in the Figure; the k₂ values of entries 4, 7, and 30 are calculated by the increasing signal of products, and the k₂ values of entries 12, 14–22, 24, and 31 are calculated by the decreasing signals of reactants.