3-Bromotetrazine: labelling of macromolecules monosubstituted bifunctional -tetrazines.

We report the synthesis and first characterisation of the novel chemical probe 3-bromotetrazine and establish its reactivity towards nucleophiles. This led to the synthesis of several novel classes of 3-monosubstituted -tetrazines. A remarkable functional group selectivity is observed and is utilised to site-selectively functionalise different complex molecules.