Tetrazine Ligation: Fast Bioconjugation Based on Inverse-Electron-Demand Diels−Alder Reactivity

Described is a bioorthogonal reaction that proceeds with unusually fast reaction rates without need for catalysis: the cycloaddition of s-tetrazine and trans-cyclooctene derivatives. The reactions tolerate a broad range of functionality and proceed in high yield in organic solvents, water, cell media, or cell lysate. The rate of the ligation between trans-cyclooctene and 3,6-di-(2-pyridyl)-s-tetrazine is very rapid (k2 2000 M−1 s−1). This fast reactivity enables protein modification at low concentration.