To a mixture of methyl 4-{[2-ethyl-1-(3-methyl-1-benzothiophen-2-yl)butyl]amino}benzoate (580 mg) synthesized above, tetrahydrofuran (10 mL) and ethanol (10 mL) was added 1N aqueous sodium hydroxide solution (10.0 mL), and the mixture was stirred overnight with heating under reflux, and concentrated under reduced pressure. The residue was dissolved in water (20 mL), and 1N hydrochloric acid (10.0 mL) was added at 0° C. The resulting precipitate was collected by filtration to give the title object compound (529 mg, 95%) as a white solid.
