Feasibility of palladium-catalyzed isotopic exchange between sodium [¹²⁵I]I and 2-iodo-para-carborane

Many ortho-/meta-/para-closo-carborane derivatives have been proposed for boron neutron capture therapy. However, it is difficult to follow their pharmacokinetics in patients, which creates a risk of suboptimal treatment. Adding a radioactive label to closo-carboranes may simplify pharmacokinetic studies. This paper reports on a study of the feasibility of palladium-catalyzed isotopic exchange of iodinated closo-carborane with radioisotopes of iodine. 2-iodo-para-carborane was selected as a model compound. It was shown that such isotopic exchange is possible and provides a high yield (83 ± 4.2%) after 40 min of reaction time. The reaction conditions were optimized, and it was demonstrated that the presence of tetra n-butylammonium hydrogensulfate is important in order to stabilize the catalyst and to give reproducibility of the labeling.