Several 1,2-closo-dodecaboranes have been synthesized from the corresponding alkynyl-substituted thiouracils to provide carboranes attached to functional group capable of being covalently incorporated into structures of potential use in the treatment of melanoma by boron neutron capture therapy (BNCT). The carboranyl functionalities were attached at the 5, 6 and N-1 positions of the thiouracil molecule.