Strategic Evaluation of the Traceless Staudinger Ligation for Radiolabeling with the Tricarbonyl Core

The traceless Staudinger ligation with its two variants is a powerful biorthogonal conjugation method not only for the connection of biomolecules, but also for the introduction of fluorescence- or radiolabels under mild reaction conditions. Herein, the strategic evaluation of the traceless Staudinger ligation for radiolabeling Tc-99m using the fac-[Tc(CO)(3)](+) core is presented. A convenient and high-yielding three-step synthetic procedure of dipicolylamine-based phosphanols as ligands for the mild radiolabeling was developed. The labeling was accomplished using a tricarbonyl kit and a Tc-99m-pertechnetate generator eluate showing 87% radiochemical conversion. The respective rhenium-based, non-radioactive reference compounds were synthesized using (Et4N)(2)[Re(CO)(3)Br-3] as precursor. All products were analyzed by NMR, MS, and elemental analysis. Additional XRD analyses were performed.