No-carrier-added [123I]1-(beta-D-arabinofuranosyl)-5(E)-(2- iodovinyl)uracil (IVaraU): high yield radiolabeling via organotin and exchange reactions.

Organotin intermediates for IVaraU synthesis were obtained following the reaction of 1-(2',3',5'-tri-O-toluyl-beta-D-arabinofuranosyl-5-iodouracil with (E)-1,2-bis(tri-(n-butyl) stannyl)ethene in the presence of catalytic (Ph3P)2PdCl2. A direct precursor for IVaraU, (E)-5-[2-tri-n-butylstannylvinyl]-arabinosyluridine, reacted with [123I]NaI (10 mCi) or alternatively [125I]NaI in the presence of methanol and chloramine T providing no-carrier-added (NCA) [123I]IVaraU in a radiolabeling yield up to 97%; the product was recovered following reversed phase HPLC. Unlabeled IVaraU was prepared in five steps from arabinosyluridine via an organotin intermediate with an overall yield of 22%. An exchange radioiodination was also identified, based on accessible BrVara U in the presence of water and a cuprous ion catalyst. [123I]NaI (up to 40 mCi) or alternatively [125I]NaI reacted under exchange conditions to give no-carrier-added [123,125I]IVaraU in a radiolabeling yield of 93%; the product was recovered following reversed phase HPLC.