Synthesis of 3-amino-1-carboxy-o-carborane and an improved, general method for the synthesis of all three C-amino-C-carboxycarboranes

Amino acids of the polyhedral carboranes have potential applications in boron neutron capture therapy and in other areas of bioorganic chemistry, but simple, general methods for their synthesis are nonexistent. A general method for synthesis of C-amino-C-carboxy derivatives of o-, m-, and p-carborane is reported, starting from their respective monoacids and proceeding through nucleophilic attack by an alcohol on the intermediate C-isocyanates. Deprotection of the resulting carbamates provides a simple method for access to the C-amines; Alternatively, the C-isocyanates can be isolated for further reactions, Carbonylation of the carbamates at the remaining carboranyl CH results in high-yield production of the carbamate-protected amino acid. Another related method for the high-yield preparation of the isomeric 3-amino-1-carboxy-o-carborane is also described which makes available for the first time all four reasonably accessible members of the series.