To a solution of 8-[4-(2-butoxyethoxy)phenyl]-1-isobutyl-1,2,3,4-tetrahydro-1-benzoazocine-5-carboxylic acid (700 mg) in tetrahydrofuran (10 ml) was added a drop of DMF. Then, after adding thionyl chloride (0.147 ml), the mixture was stirred under nitrogen atmosphere for 1 hour. The resulting solution was slowly added dropwise to a solution of ethyl 4-(2-(((4-aminophenyl)sulfanyl)methyl)imidazol-1-yl)butanoate (544 mg) in pyridine (10 ml) at 0° C. under nitrogen atmosphere. After stirring overnight at room temperature and under nitrogen atmosphere, to the reaction mixture was added water and the mixture was extracted with ethyl acetate. The organic layer was washed twice with water and once with saturated brine, and dried with magnesium sulfate. The solvent was distilled off under reduced pressure, and the resulting residue was purified with basic silica gel column chromatography (hexane:ethyl acetate=1:1→ethyl acetate), and re-crystallized from hexane-ethyl acetate to give ethyl 4-(2-(((4-(((8-(4-(2-butoxyethoxy)phenyl)-1-isobutyl-1,2,3,4-tetrahydro-1-benzoazocine-5-yl)carbonyl)amino)phenyl)sulfanyl)-methyl)imidazol-1-yl)butanoate (1.03 g) (Compound 33) as yellow crystals.
