One-pot synthesis of an indole-substituted 7,8-dicarba-nido-dodecahydroundecaborate(-1)

Half- and mixed-sandwich metallacarboranes for potential applications in medicine

Today, medicinal chemistry is still clearly dominated by organic chemistry, and commercially available boron-based drugs are rare. In contrast to hydrocarbons, boranes prefer the formation of polyhedral clusters via delocalized 3c2e bonds, such as polyhedral dicarba-closo-dodecaborane(12) (closo-C2B10H12). These clusters have remarkable biological stability, and the three isomers, 1,2- (ortho), 1,7- (meta), and 1,12-dicarba-closo-dodecaborane(12) (para), have attracted much interest due to their unique structural features. Furthermore, anionic nido clusters ([7,8-C2B9H11]2−), derived from the neutral icosahedral closo cluster 1,2-dicarba-closo-dodecaborane(12) by deboronation followed by deprotonation are suitable ligands for transition metals and offer the possibility to form metallacarboranes, for example via coordination through the upper pentagonal face of the cluster. The isolobal analogy between the cyclopentadienyl(–1) ligand (Cp−) and [C2B9H11]2− clusters (dicarbollide anion, Cb2−) is the motivation in using Cb2− as ligand for coordination to a metal center to design compounds for various applications. This review focuses on potential applications of half- and mixed-sandwich-type transition metal complexes in medicine.

nido-Dicarbaborate Induces Potent and Selective Inhibition of Cyclooxygenase-2

Carbaboranes are increasingly studied as pharmacophores, particularly as replacements for aromatic systems. However, especially ortho-carbaborane is prone to degradation of the cluster, which hampers biological application. This study demonstrates that deboronation of the cluster may not only lead to a more active analogue, but can also improve the solubility and stability of a carbaborane-containing inhibitor. Notably, introduction of a nido-dicarbaborate cluster into the cyclooxygenase (COX) inhibitor indomethacin results in remarkably increased inhibitory potency and selectivity for COX-2 relative to the respective phenyl analogue. The first crystal structure of a carbaborane-containing inhibitor bound to COX-2 further reveals a novel binding mode for the inhibitor that is strikingly different from that of indomethacin. These results indicate that nido-dicarbaborate is a promising pharmacophore that exhibits properties which are also highly beneficial for its introduction into other inhibitor classes.