Labelling of carbaboranyl compounds with a selenium atom with a view to applications in boron-neutron-capture therapy (BNCT) and positron-emission tomography (PET)

We synthesized 2'-carbaboranyl-2,5'-bi-1H-benzimidazoles containing 10 B-at oms and labeled with Se or the positron-emitting radionuclide Se-73 (t(1/2) = 7.1 h), with a view to their application to cancel. treatment by boron-n eutron-capture therapy (BNCT) and to compound-distribution measurements in vivo by positron-emission tomography (PET). Thus, 2,2'-{[2'-(4-[1,2-dicarba -closo-dodecaboran(12)-2-ylmethoxy]phenyl]-[2,5'-bi-1H-benzimidazol]-5-yl}i mino)bis[ethanol] (26c) was obtained by the reaction of 2,2'-[(3,4-diaminep henyl)imino]bis[ethanol] (19) with ethyl 2-{4-[1,2-dicarba-closo-dodecabora n(12)-2-ylmethoxy]phenyl}-1H-benzimidazole-5-carboximidate hydrochloride (2 5), as well as the analogues 26a and 26b (Scheme 6). Tosylation of compound 26c gave 4 regioisomers 27a-d, which, after selenation, produced 2'-{4-[1, 2-dicarba-closo-dodecaboran(12)-2-ylmethoxy]phenyl}-5-(tetrahydro-2H-1,4-se lenazin-4-yl)-2,5'-bi-1H-benzimidazole (29) in 42% yield (Scheme 7).