Methyl 6-[(2-{[(5-chloropyridin-2-yl)amino]-carbonyl}benzofuran-3-yl)amino]-6-oxohexanoate (4.30 g) obtained in Example 10(1) is suspended in methanol (5 m), and thereto is added at room temperature 2N aqueous sodium hydroxide solution (30 ml). The mixture is stirred at room temperature for 4 hours, and at 50° C. for 2 hours. The reaction solution is diluted with water and acidified by addition of 10% hydrochloric acid under ice-cooling, and the precipitates are collected by filtration and dried to give the title compound (3.54 g). ESI-MS M/Z:414/416[M−H]−
