From ortho-carbaborane-9-thiol towards new building blocks

The potential of 1,2-dicarba-closo-dodecaborane(12)-9-thiol, 9-HS-1,2-closo-C2B10H11, for the design of novel building blocks is highlighted by two examples envisioned for incorporation into tumor-selective peptides for boron neutron capture therapy (BNCT). By employing a t-Bu protection strategy the synthesis of a bis-galactosyl-substituted ortho-carbaborane carboxylic acid was elaborated, and the procedure is suggested as a general approach towards carbaboranes with three substituents. Furthermore, a simple route to a tris(ortho-carbaborane) building block starting from pentaerythritol is illustrated. All compounds were synthesized in moderate to high yields and identified by H-1, B-11, and C-13 NMR spectroscopy, IR spectroscopy, mass spectrometry, and in one case by X-ray crystallography. (C) 2012 Elsevier Ltd. All rights reserved.