Dithiol Aryl Arsenic Compounds as Potential Diagnostic and Therapeutic Radiopharmaceuticals

Arsenic-72 (72As) and 77As have nuclear properties useful for positron emission tomography (PET) and radiotherapy, respectively. The thiophilic nature of arsenic led to the evaluation of dithioarylarsines for potential use in radiopharmaceuticals. Several dithioarylarsines were synthesized from their arylarsonic acids and dithiols and were fully characterized by NMR, ESI-MS, and X-ray crystallography. This chemistry was translated to the no-carrier-added (nca) 77As level. Because arsenic was available at the nca nanomolar level only as [77As]arsenate, this required addition of an aryl group directly to the As to form the [77As]arylarsonic acid. The [77As]arsenate was reduced from 77As (V) to 77As (III), and a modified Bart reaction was used to incorporate the aryl ring onto the 77As, which was followed by dithiol addition. Various modifications and optimizations resulted in 95% radiochemical yield of nca [77As]p-ethoxyphenyl-1,2-ethanedithiolatoarsine.