A Novel Versatile Precursor Suitable for 18F- Radiolabelling via “Click-Chemistry”

As an effort to improve 18F radiolabelling of biomolecules in terms of method robustness and versatility, we report the synthesis and radiolabelling of a new azido precursor potentially useful for the so called “click-reaction”, in particular the ligand-free version of the copper(I)-catalyzed alkyne-azide cycloaddition (CuAAC). The new azido precursor may help to overcome problems sometimes exhibited by most of the currently used analogues, as it is safe to handle and it displays long term chemical stability, thus facilitating the development of new radiolabelling procedures. Moreover, the formed 18F labelled 1,2,3-triazole is potentially metabolically stable, and could enhance the in vivo circulation time. The above azido precursor was successfully radiolabelled with 18F, with 51% radiochemical yield (non-decay-corrected). As a proof of concept, the 18F labelled azide was then tested with a suitable alkyne functionalized aminoacid (L-propargylglycine), showing 94% of conversion, and a final radiochemical yield of 27% (>99% radiochemical purity), non-decay-corrected, with a total preparation time of 104 min.