Synthesis of purine conjugates with bis-carboranyl derivatives of (S)-lysine or (S)-glutamic acid

A number of new purine and 2-aminopurine conjugates with closo- or nido-carborane fragments attached via polyfunctional amino acid residues were synthesized. Derivatives of (S)-lysine and (S)-glutamic acid containing two closo-carborane residues and a free carboxyl group were used as boron-containing building blocks. It has been found that the obtained purine and 2-aminopurine conjugates containing 18–20 boron atoms per molecule possess good solubility in water and aqueous ethanol (up to 75 mg/mL), which allows us to consider them as potential agents for boron delivery to tumor cells in boron neutron capture therapy.