In a reaction vessel, 2-(4-{2-[4-(1H-benzoimidazol-2-yl)-piperidin-1-yl]-ethyl}-phenyl)-2-methyl-propionic acid methylester (0.5 g) prepared in the Example 13, potassium-t-butoxide (0.14 g), ethoxyethylmesylate (0.25 g) and DMF (20 mL) were introduced, and the mixture was reacted at 50□ for 3 hours. Distilled water (50 mL) and ethylacetate (50 mL) were added thereto, and the mixture was stirred to separate a layer. Separated organic layer was washed with distilled water (50 mL), dehydrated, and condensed under reduced pressure to obtain 2-[4-(2-{4-[1-(2-ethoxy-ethyl)-1H-benzoimidazol-2-yl]-piperidin-1-yl}-ethyl)-phenyl]-2-methyl-propionic acid methylester (0.5 g, yield 85%, HPLC purity 98.5% or more).
