[CH:1]([O:4][C:5]1[C:14]([O:15][CH3:16])=[CH:13][C:8]([C:9]([O:11]C)=[O:10])=[C:7]([NH:17][CH2:18][C:19]2[CH:24]=[CH:23][C:22]([O:25][CH3:26])=[CH:21][CH:20]=2)[CH:6]=1)([CH3:3])[CH3:2].CO.[OH-].[Na+]>O1CCCC1>[CH:1]([O:4][C:5]1[C:14]([O:15][CH3:16])=[CH:13][C:8]([C:9]([OH:11])=[O:10])=[C:7]([NH:17][CH2:18][C:19]2[CH:20]=[CH:21][C:22]([O:25][CH3:26])=[CH:23][CH:24]=2)[CH:6]=1)([CH3:3])[CH3:2]A mixture of methyl 4-isopropoxy-5-methoxy-2-(4-methoxybenzyl)aminobenzoate (18.9 g), methanol (50 ml), tetrahydrofuran (150 ml) and a 1N aqueous sodium hydroxide solution (80 ml) was stirred at room temperature for 1 night, heated under reflux for 12 hours. The solvent was distilled off under reduced pressure, the reaction mixture was adjusted to about pH 6 by adding 1N hydrochloric acid and 5% citric acid. The precipitated solid was collected by filtration, washed and dried to obtain the target compound (18.0 g).
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