While trifluoroacetic acid (17 mL) was stirred under cooling with ice, 1-tert-butoxycarbonyl-4-[2-(5-fluorobenzimidazol-2-ylthio)ethyl]piperazine (6.50 g, 17.08 mmol) was added to the acid over 30 minutes and dissolved thereto. The temperature of the mixture was allowed to room temperature, and the mixture was stirred for 30 minutes. Thereafter, ether and hexane were added thereto, and the formed solid was collected through filtration. The collected product was washed with ether, to thereby yield 1-[2-(5-fluorobenzimidazol-2-ylthio)ethyl]piperazine tris(trifluoroacetic acid) salt (10.50 g, yield 99%) as a brown powder.
