Synthesis of Charge-Compensated nido -Carboranyl Derivatives of Sulfur-Containing Amino Acids and Biotin.

A new group of charge-compensated nido -carboranyl derivatives of sulfur-containing amino acids and biotin has been synthesized in which the boron atom in position 9 or 10 of carborane is attached to a positively charged sulfur atom. The possibilities of obtaining symmetrical B(10)-substituted and asymmetric B(9)-substituted nido -carboranes were studied. Using the example of ( S )-methionine and D-biotin derivatives, water-soluble S-substituted charge-compensated nido -carboranes with free functional groups were prepared. The results obtained open up prospects for the development of potential boron delivery agents for BNCT as well as new bioactive compounds containing a negatively charged nido -carboranyl fragment bearing a positive charge on the sulfur atom associated with the boron cluster.