New strategy for synthesis of mercaptoundecahydrododecaborate derivatives via click chemistry: possible boron carriers and visualization in cells for neutron capture therapy.

A new method that utilizes the click cycloaddition reaction to functionalize B(12)H(11)SH(2-) (BSH) with organic molecules was investigated. S,S-Dipropargyl-SB(12)H(11)(-) (1) and S-propargyl-SB(12)H(11)(2-) (4) were prepared from [(CH(3))(4)N](2)B(12)H(11)SH and [(CH(3))(4)N](2)B(12)H(11)S(CH(2))(2)CN (2) with propargyl bromide, respectively. Compound 1 or 4 reacted with various azides with mediation by Cu(II) ascorbate to give the corresponding bis-triazolo BSH derivatives (1-) or monotriazole BSH derivatives (2-), respectively, in excellent yields. The click cycloaddition reaction is very useful not only for the synthesis of various BSH-containing organic compounds for boron neutron capture therapy (BNCT) but also for the visualization of boron clusters in cells. We succeeded in the click cycloaddition reaction of compound 1 with Alexa Fluor 488 azide dye and found that 1 accumulated not in the cytoplasm but in the nuclei of HeLa cells.