5.50 g of the amorphous compound obtained in Example 122 was dissolved in 30 ml of methanol and 30 ml of tetrahydrofuran, to the solution was added 60 ml of 1N sodium hydroxide, and the mixture was refluxed for 2 hours and then cooled. The reaction mixture was acidified with citric acid and then alkalized with sodium bicarbonate, resulting insoluble matter was dissolved with a small amount of methanol, and the solution was extracted twice with 400 ml of chloroform. The extract was dried over magnesium sulfate and evaporated to remove the solvent under a reduced pressure, and resulting residue was applied to a silica gel column and eluted with chloroform/methanol (20:1) to obtain 3.1 g of the title compound in a colorless amorphous form.
