DESIGN AND SYNTHESIS OF CARBORANYL PEPTIDES AS CARRIERS OF 1,2-DICARBADODECARBORANE CLUSTERS

The carboranyl amino acid arba-closo-dodecarborane(12)-1-yl-2-aminopen tanoic acid protected as the Boc derivative 1 has been used for the sy nthesis of peptides 2a- 10 differing in chain length and boron content . Alternating the bulky hydrophobic Boc-carboranyl amino acid 1 with h ydrophilic residues like serine led to a remarkable improvement in sol ubility of the peptides without the need to convert the closo-carboran e cages into the anionic nido-forms. Conventional procedures of soluti on peptide synthesis were used, employing the mixed-anhydride method f or the condensation steps, the tert-butoxycarbonyl group for intermedi ate N(alpha)-protection and benzyl-type groups for side-chain protecti on, resulting in good overall yield. Both acidolytic and hydrogenolyti c deprotection steps did not harm the closo-carborane cage. Hydrogenol ysis reduced the yields of 5 and 10 drastically due to strong adsorpti on onto the palladium catalyst.