C[O:2][C:3]([C:5]1[CH:6]=[C:7]2[C:11](=[CH:12][C:13]=1[C:14]([O:16]C)=[O:15])[NH:10][CH:9]=[CH:8]2)=[O:4].C(O)C.[OH-].[Na+].Cl>O>[NH:10]1[C:11]2[C:7](=[CH:6][C:5]([C:3]([OH:4])=[O:2])=[C:13]([C:14]([OH:16])=[O:15])[CH:12]=2)[CH:8]=[CH:9]1To a stirred solution of the dimethyl ester produced in step d (1.14 g, 4.9 mmol) in a 5:1 mixture of ethanol:water (12 ml) was added solid sodium hydroxide (0.49 g, 12.4 mmol). The solution was stirred at a gentle reflux for 3 h. The solution was acidifed on cooling to pH2 with hydrochloric acid and then evaporated. The residue was azeotroped with ethanol and then toluene and dried under vacuum. The residue was then extracted with hot acetone (5×20 ml) and the combined extracts were evaporated to leave the title compound (870 mg).
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