Copper-free click bioconjugation of technetium-99m complexes using strained cyclononyne derivatives.

Click chemistry, in particular copper-free click reactions, has gained growing interest for radiolabelling purposes in the field of radiopharmaceutical sciences. [Tc][Tc(CO)(HO)] works as an excellent starting complex for the radiolabelling of biomolecules under mild conditions. A new chelator, investigated for the copper-free strain-promoted cycloaddition (SPAAC), was synthesised containing the 2,2'-dipicolylamine (DPA) moiety for the Tc-tricarbonyl core and compared with a DPA chelator based on activated esters for conventional radiolabelling.