Closomers of high boron content: Synthesis, characterization, and potential application as unimolecular nanoparticle delivery vehicles for boron neutron capture therapy

Unique nanosized closomers of high boron content that may exhibit potential as boron neutron capture therapy target species have been synthesized. The design of these boron-rich nanospheres is based in part on previous work involving dodeca(carboranyl)-substituted closomers [Thomas, J.; Hawthorne, M. F. Chem. Commun. 2001, 1884-1885]. Coupling of ortho-carborane moieties through ester and ether linkages to the rigid [closo-B₁₂(OH) ₁₂]^2- scaffold resulted in the development of a 12(12)-closomer-ester derivative, dodeca[6-(1,2-dicarba-closo-dodecaboran-1-yl) hexanoate]-closo-dodecaborate (2-), 6, and 12(12)-closomer-ether derivatives, dodeca[6-(2-methy1-1,2-dicarba-nido-dodecaboran-1-yl)hexyl]-closo-dodecaborane (14-), 14, and dodeca[6-(7,8-dicarba-nido-dododecaboran-7-yl)hexyl]-closo- dodecaborane (14-), 15. These closomers were investigated by UV-visible spectroscopy and cyclic voltammetry. Additionally, a deboronation method employing NaCN as the nucleophilic reagent was utilized to obtain sodium salts of the ether-linked nido-closomer polyanions, which were purified using a newly developed size-exclusion high pressure liquid chromatography method.