Synthesis of triazolyl methyl-substituted amino- and oxy-undecahydrododecaborates for potential application in boronneutron capture therapy

Abstract

A general approach to the synthesis of triazole conjugates containing undecahydro-closo-dodecaborate anions based on Huisgen 1,3-dipolar cycloaddition is presented. Undecahydro-closo-dodecaborate anions bearing terminal alkyne groups were synthesized by the reaction of H₃N–B₁₂H₁₁⁻ or HO–B₁₂H₁₁²⁻ with alkyne halides in N,N-dimethylformamide using KOH as a base. Variation of reaction time, alkyne halide concentration and steric demands of the alkyne halide resulted in the stepwise introduction of one to three alkyne groups into H₃N–B₁₂H₁₁⁻. Two compounds {(CHCCH₂)₃N–B₁₂H₁₁⁻ and (CHCCH₂)O–B₁₂H₁₁²⁻} were crystallized for single-crystal X-ray diffraction studies. N- and O-alkyne undecahydro-closo-dodecaborate anions reacted with various functionalized azides including lipid, carborane, aryl and hydroxyalkyl groups. The current study provides various synthetic applications not only for BNCT but also for boron cluster materials.