Thiomethyltetrazines Are Reversible Covalent Cysteine Warheads Whose Dynamic Behavior can be "Switched Off" Bioorthogonal Chemistry Inside Live Cells.

Electrophilic small molecules that can reversibly modify proteins are of growing interest in drug discovery. However, the ability to study reversible covalent probes in live cells can be limited by their reversible reactivity after cell lysis and in proteomic workflows, leading to scrambling and signal loss. We describe how thiomethyltetrazines function as reversible covalent warheads for cysteine modification, and this dynamic labeling behavior can be "switched off" bioorthogonal chemistry inside live cells.

Divergent Synthesis of Monosubstituted and Unsymmetrical 3,6-Disubstituted Tetrazines from Carboxylic Ester Precursors.

Since tetrazines are important tools to the field of bioorthogonal chemistry, there is a need for new approaches to synthesize unsymmetrical and 3-monosubstituted tetrazines. Described here is a general, one-pot method for converting (3-methyloxetan-3-yl)methyl carboxylic esters into 3-thiomethyltetrazines. These versatile intermediates were applied to the synthesis of unsymmetrical tetrazines through Pd-catalyzed cross-coupling and in the first catalytic thioether reduction to access monosubstituted tetrazines.