The TCO‐tetrazine click reaction is a very powerful tool in catalyst‐free protein–protein bioconjugation. The reaction follows an inverse‐electron demand Diels‐Alder cycloaddition reaction of trans‐cyclooctene (TCO) with tetrazine, which is a bioorthogonal reaction that possesses exceptional kinetics (k > 800 M‐1s‐1) and selectivity. Such excellent reaction rate constants are unparalleled by any other bioorthogonal reaction pair described to date.
The extremely fast kinetics and selectivity enables the conjugation of two low abundance biopolymers in an aqueous and otherwise complex chemical environment through the formation of a stable dihydropyridazine. This bioorthogonal reaction possesses extreme selectivity and biocompatibility, such that the complimentary reagents can form covalent bonds within richly functionalized biological systems, in some cases, living organisms.