Copper-mediated isotopic exchange between [125I]iodide and bis(triethylammonium) undecahydro-12-iodo-closo-dodecaborate in aqueous media

Derivatives of dodecahydro-closo-dodecaborate(2-) anion were proposed as boron-rich compounds for boron-neutron capture therapy (BNCT) of malignant tumours. Labeling of such tumour-targeting compounds with radioisotopes would facilitate the investigation of their pharmacokinetics and help to optimize patient treatment protocols. Earlier, we reported the feasibility of labeling of closo-dodecaborate(2-) by isotopic exchange in molten acetamide. In this study, the feasibility of low-temperature isotopic exchange in the system [125I]iodide - bis(triethylammonium) undecahydro-12-iodo-closo-dodecaborate was investigated. Our attempts to perform the exchange in solvents such as methylene chloride, acetone and acetonitrile in the presence of phase-transfer catalysts were unsuccessful. However, copper mediated exchange in aqueous media was possible. Isotopic exchange of triethylammonium undecahydro-12-iodo-closo-dodecaborate provided a 90-95% labeling yield after heating for three and half hours at 100 °C.