Rhenium (186/188Re) and technetium (99mTc) radioisotopes have shown significant promise for therapeutic and diagnostic applications, respectively. The two metals have very similar chemistries, and as such are considered a theranostic matched pair. Extensive work has gone into designing ligands for use with 99mTc due to its ideal imaging properties (6-h half-life, 140 keV g) leading to prevalent use in medicine. Slight differences between Tc and Re reactivity mean that not all the existing ligands used with 99mTc are suitable for use with Re. However, complexes of the type trans-[Tc(PR3)2(Schiff base)]+, known as the Tc Q-series have proven useful for myocardial perfusion imaging and multidrug resistant (MDR) tumor imaging, and have potential to work with 186/188Re as well as 99mTc. Salicylaldehyde based N2O2 Schiff base ligands have been used to generate a range of Tc(III) and Re(III) compounds for potential use as radiopharmaceuticals. In addition to theranostic potential, these N2O2 Schiff base ligands may also serve as bifunctional chelates by appending a targeting vector onto the backbone of the ligand. We have shown that chelates of this type differing only in their backbone makeup have significantly different rates of conversion from the trans-M(III) to cis-M(V) configuration, which occurs as the metal centers are oxidized. These oxidation rates differ not only between complexes with different backbones, but also between complexes of the same ligand with different metal centers. Characterization using NMR, UV-vis, X-ray crystallography, cyclic voltammetry, and mass spectrometry as well as HPLC separation of radiolabeled complexes have given insight into these stability differences, which will be discussed.

Comparing stabilities of bifunctional N2O2 schiff base ligands for Tc(III) and Re(III) radiopharmaceuticals

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.