The compound (838.4 mg) obtained in Example 4, (b) was dissolved in 16 ml of dichloromethane, and with stirring at 10° C., a solution of 525 mg of sulfamic acid in 9.5 ml of water was added, followed by addition of a solution of 262.8 mg of sodium chlorite in 0.6 ml of water. The mixture was stirred for 1 hour at the same temperature. The reaction mixture was allowed to separate. The dichloromethane layer was washed with water and then with a saturated aqueous solution of sodium chloride, and then dried over magnesium sulfate. The solvent was distilled off, and the residue was recrystallized from ethyl ether to afford 685 mg of the desired product.
