Carbaboranes as Pharmacophores: Properties, Synthesis, and Application Strategies

Carbaboranes for medicinal applications are preferably used to design boron neutron capture therapy (BNCT) agents. Connection of the cluster to a tumor-targeting vector is a common principle in the design of BNCT agents and is aimed to improve the tumor-to-blood ratio. The carbon and boron atoms of the C2B10 core are hexacoordinate to compensate for the low electron density, forming 20 triangular faces. Carbaboranes are closo clusters and feature 2n + 2 skeletal electrons, which reveal nonclassical bonding interactions giving a very complex overall electronic structure. The icosahedral carbaborane structure results in a spherical presentation of only slightly polarized hydrogen atoms. The presence of the 10 rather hydride-like hydrogens at the boron atoms makes the clusters extremely hydrophobic. Carbon-substituted carbaboranes can be prepared by reaction of substituted acetylenes with decaborane. The integration of carbaboranes in place of central ring systems changes the biological profile of the lead structure.