Esterified B12 icosahedra with totally organoderivatized surfaces are obtained from the reaction of [closo‐B12(OH)12]2− with acetic anhydride or benzoyl chloride. The resulting “closomers”, in which each cluster vertex is substituted with an organic ester moiety, can provide camouflaged modules of variable size, shape, charge, hydrophobicity, etc. and represent the first examples of this structural motif known in chemistry. The figure displays, in a space‐filling representation, the result of an X‐ray analysis performed with the dodecabenzoate ester derivative.
The successful treatment of cancer by boron neutron capture therapy (BNCT) requires the selective concentration of boron-10 within malignant tumors. The potential of liposomes to deliver boron-rich compounds to tumors has been assessed by examination of the biodistribution of boron delivered by liposomes in tumor-bearing mice. Small unilamellar vesicles have been found to stably encapsulate high concentrations of water-soluble ionic boron compounds. Alternatively, lipophilic boron-containing species have been embedded within the phospholipid bilayer of liposomes, and both hydrophilic and lipophilic boron compounds have been incorporated within the same liposome formulation. The biodistribution of boron was determined at several time points over 48 hr after i.v. injection of liposomal suspensions in BALB/c mice bearing EMT6 tumors. The tumor-selective delivery of boron by the liposomes was demonstrated as tumor-boron concentrations increased for several hours post-injection. Even at the low injected doses employed (6-18 mg boron/kg body weight) therapeutic tumor boron concentrations were observed (> 30 micrograms boron/g tissue) and high tumor/blood ratios were achieved (> 5). The most favorable results were obtained with the polyhedral borane Na3[a2-B20H1-NH2CH2CH2NH2]. Liposomes encapsulating this species produced a tumor boron concentration of 45 micrograms/g tissue at 30 hr post-injection, at which time the tumor/blood boron ratio was 9.3.
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