Synthesis of dodecaborate-conjugated cholesterols for efficient boron delivery in neutron capture therapy

Dodecaborate-conjugated cholesterols 3a–c were synthesized for liposomal boron delivery systems in neutron capture therapy. The current synthesis is based on the S-alkylation protocol of the cyanoethyl-protected BSH with alkyl halides. The dodecaborate-conjugated cholesterol 3a liposome, which was prepared from dimyristoylphosphatidylcholine (DMPC), cholesterol, dodecaborate-conjugated cholesterol 3a, and polyethyleneglycol-conjugated distearoylphosphatidylethanolamine (PEG-DSPE) (1:0.5:0.5:0.1), exhibited higher cytotoxicity than BSH at the same boron concentration and IC50 values of the 3a liposome and BSH toward colon 26 cells were estimated as 25 and 78 ppm of boron concentration, respectively.