(E)-[2-(2-Propylbenzimidazol-1-yl)methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-ylidene]acetic acid (80 mg, 0.189 mmol) obtained in Example 2 was dissolved in 1,2-dimethoxyethane (0.7 mL), N-methylmorpholine (62 μL, 0.567 mmol) and isobutyl chlorocarbonate (49 μL, 0.378 mmol) were added, and the mixture was stirred at room temperature for 1 hr. The reaction mixture was filtered, and the filtrate was added to a solution (0.6 mL) of sodium borohydride (36 mg, 0.945 mmol) in water at 0° C., and the mixture was stirred for 10 min. Water was added to the mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (chloroform/methanol=95/5) to give the title compound (compound 13) (43 mg, 55%).
