[CH3:1][S:2]([NH:5][C:6]1[C:24]([O:25][C:26]2[CH:31]=[CH:30][CH:29]=[CH:28][CH:27]=2)=[CH:23][C:9]2[C:10](=[O:22])[C:11]([N:14]([CH:20]=[O:21])[CH2:15][C:16]([O:18]C)=[O:17])=[CH:12][O:13][C:8]=2[CH:7]=1)(=[O:4])=[O:3].Cl>[OH-].[Na+]>[CH3:1][S:2]([NH:5][C:6]1[C:24]([O:25][C:26]2[CH:31]=[CH:30][CH:29]=[CH:28][CH:27]=2)=[CH:23][C:9]2[C:10](=[O:22])[C:11]([N:14]([CH2:15][C:16]([OH:18])=[O:17])[CH:20]=[O:21])=[CH:12][O:13][C:8]=2[CH:7]=1)(=[O:3])=[O:4]In 45 ml of a 1N aqueous sodium hydroxide solution was dissolved 4.46 g of 7-methylsulfonylamino- 3-(N-formyl-N-methoxycarbonylmethylamino)-6-phenoxy-4H-1-benzopyran-4-one. The solution was stirred for 1.5 hours at 25°-30° C. The solution was then adjusted to pH 3 with 4N hydrochloric acid and extracted with two 50-ml portions of ethyl acetate. The extracts (the organic layers) were combined, washed with water and a saturated aqueous sodium chloride solution in this order, and dried with anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure. The residue was mixed with diethyl ether. The resulting crystal was collected by filtration to obtain 3.57 g (yield: 82.6%) of 7-methylsulfonylamino-3-(N-carboxymethyl-N-formylamino)-6-phenoxy-4H-1-benzopyran-4-one having a melting point of 98°-100° C.
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