Scandium trifluoromethanesulfonate (609 mg) was added to a mixture of the compound (500 mg) obtained in Step 3 of Example 1, 4-methylaminobenzoic acid (343 mg) and anhydrous acetonitrile (10 mL) under cooling with ice-water, and the mixture was stirred at room temperature for sixty eight hours under nitrogen atmosphere. Water (50 mL) and acetonitrile (10 mL) were added to the resulting mixture and the pH of the mixture was adjusted to above 9 with sodium hydrogen carbonate, insoluble matter was removed by filtration and the filtrate was concentrated under reduced pressure. Water in the residue was removed by azeotrope with ethanol, soluble components in the residue were dissolved in ethanol and the insoluble matter was removed by filtration. The filtrate was concentrated under reduced pressure and then, the residue was dissolved in water (50 mL) and the pH of the solution was adjusted to 7 by diluted hydrochloric acid. Precipitate was collected by filtration and washed with water and ethyl acetate successively under stirring. The precipitate was collected by filtration and dried to obtain the titled compound (524 mg) as powder.
