4-[2-(2-hydroxyethoxy)-ethyl]-piperazine-carboxylic acid (2-phenylsulfanyl-phenyl)-amide (4 g, 10 mmol), triethylamine (2 ml, 15 mmol) and toluene (50 ml) were charged into a reaction flask. Benzoyl chloride (1.7 g, 12 mmol) in toluene (5 ml) was added at 0-10° C. The mixture was stirred for 16 h at 20° C. Cold water (50 ml) and 1 M NaOH (100 ml) were added. The mixture was stirred for 20 min. The water phase was separated. The organic phase was washed with saturated NaCl solution (25 ml) and evaporated in vacuo. The yield of benzoic acid 2-{2-[4-(2-phenylsulfanyl-phenylcarbamoyl)piperazin-1-yl]-ethoxy}-ethyl ester was 4.91 g.
