Selective Chelation of the Exotic Meitner‐Auger Emitter Mercury‐197 m/g with Sulfur‐Rich Macrocyclic Ligands: Towards the Future of Theranostic Radiopharmaceuticals

Abstract

Abstract Mercury‐197 m/g are a promising pair of radioactive isomers for incorporation into a theranostic as they can be used as a diag nostic agent using SPECT imaging and a thera peutic via Meitner‐Auger electron emissions. However, the current absence of ligands able to stably coordinate 197m/g Hg to a tumour‐targeting vector precludes their use in vivo. To address this, we report herein a series of sulfur‐rich chelators capable of incorporating 197m/g Hg into a radiopharmaceutical. 1,4,7,10‐Tetrathia‐13‐azacyclopentadecane (NS 4 ) and its derivatives, (2‐(1,4,7,10‐tetrathia‐13‐azacyclopentadecan‐13‐yl)acetic acid (NS 4 ‐CA) and N‐ benzyl‐2‐(1,4,7,10‐tetrathia‐13‐azacyclopentadecan‐13‐yl)acetamide (NS 4 ‐BA), were designed, synthesized and analyzed for their ability to coordinate Hg 2+ through a combination of theoretical (DFT) and experimental coordination chemistry studies (NMR and mass spectrometry) as well as 197m/g Hg radiolabeling studies and in vitro stability assays. The development of stable ligands for 197m/g Hg reported herein is extremely impactful as it would enable their use for in vivo imaging and therapy, leading to personalized treatments for cancer.