[CH2:1]([O:8][CH2:9][C:10]1[CH:18]=[C:17]([O:19][CH2:20][O:21][CH3:22])[CH:16]=[C:15]([O:23][CH2:24][O:25][CH3:26])[C:11]=1[C:12]([OH:14])=[O:13])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[Br:27]N1C(=O)CCC1=O.O>CN(C)C=O>[CH2:1]([O:8][CH2:9][C:10]1[C:18]([Br:27])=[C:17]([O:19][CH2:20][O:21][CH3:22])[CH:16]=[C:15]([O:23][CH2:24][O:25][CH3:26])[C:11]=1[C:12]([OH:14])=[O:13])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=12-(Benzyloxymethyl)-4,6-bis(methoxymethoxy)benzoic acid (60 mg, 0.17 mmol) obtained in Step 6 of Example 22 was dissolved in N,N-dimethylformamide (10 mL), and N-bromosuccinimide (62 mg, 0.35 mmol) was added thereto followed by stirring at a room temperature for 2 hours. The reaction mixture was added with water and extracted with chloroform 3 times. The organic layers were combined and sequentially washed with saturated aqueous sodium thiosulfate solution and saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure and the obtained residue was purified by preparative thin-layer chromatography (chloroform/methanol=20/1) to obtain 2-(benzyloxymethyl)-3-bromo-4,6-bis(methoxymethoxy)benzoic acid (16 mg, 22%).
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