To a mixture of 1-(4-chlorobenzyl)-1H-indole-7-carboxylic acid (0.20 g), methyl 4-(aminomethyl)-3-chlorobenzoate hydrochloride (0.18 g), and HATU (0.32 g) in DMF (4.0 mL) was added diisopropylethylamine (0.29 ml) under ice-cooling, followed by stirring at room temperature for 14 hours. After ice-cooled again, a 5% aqueous citric acid solution (8.0 mL) was added thereto, and the precipitated solid was collected by filtration, sequentially washed with water and diisopropylether, and dried at 60° C. under reduced pressure. To the obtained solid were added methanol (3.0 mL), THF (3.0 mL), and a 1 M aqueous sodium hydroxide solution (2.0 mL), followed by stirring at 60° C. for 2 hours. The reaction mixture was left to be cooled, a 10% aqueous citric acid solution (5.0 mL) was added thereto, and the precipitated solid was collected by filtration, washed with water, and dried at 60° C. under reduced pressure to obtain 3-chloro-4-[({[1-(4-chlorobenzyl)-1H-indol-7-yl]carbonyl}amino)methyl]benzoic acid (0.24 g).
