Boron derivatives are important in Boron Neutron Capture Therapy (BNCT) for selective tumour targeting in the presence of healthy cells. Cluster compounds, especially meta- and para-carbaboranes are used to deliver boron to the target cells. Carbaboranes exhibit a high boron content, low toxicity and very high kinetic stability. Additionally, they can be easily incorporated into (bio)chemical structures. New boron compounds are designed by a combination of tumor-targeting strategies: use of phosphonato groups as phosphate mimetics and galactosyl groups that allow specific bonding to lectins on the surface of tumour cells. A further strategy is the incorporation of carbaborane-containing amino acids into carrier peptides.
Besides their three-dimensional aromaticity, carbaboranes also exhibit extremely high hydrophobicity.
Therefore, they can be incorporated instead of phenyl groups as pharmacophoric moieties in biologically active structures, e.g., aspirin.
Phosphine-substituted amino acids are synthesised and coordinated to catalytically active transition metals after incorporation in proteins. The protein pockets should enable stereoselective catalysis.