A solution of 5.90 g (7.29 mmol) of 1,3-bis[4-[4-(4-isopropoxy-3,5-dimethoxyphenyl) benzoyl]-l-piperazinyl]propane in isopropanol (90 mL) was heated to 50° C. and a solution of 1.41 g (14.7 mmol) of methanesulfonic acid in isopropanol (30 mL) was added. t-Butyl methyl ether (30 mL) was added and the mixture was stirred for 5 minutes at 50° C., for 30 minutes at room temperature, then for 30 minutes in an ice bath. Precipitates were collected by filtration and washed with t-butyl methyl ether to afford 6.54 g of 1,3-bis[4-[4-(4-isopropoxy-3,5-dimethoxyphenyl)benzoyl]-1-piperazinyl]propane dimethanesulfonate as a colorless crystalline powder (yield: 90a). mp: 235.5° C. (decomposed).
