[Cl:1][C:2]1[C:15]2[C:10](=[C:11]([OH:16])[CH:12]=[CH:13][CH:14]=2)[C:9]([OH:17])=[C:8]2[C:3]=1[C:4](=[O:19])[CH:5]=[CH:6][C:7]2=[O:18].O.[O:21]1CC[CH2:23][CH2:22]1>C(OC(=O)C)(=O)C.N1C=CC=CC=1>[C:22]([O:16][C:11]1[CH:12]=[CH:13][CH:14]=[C:15]2[C:10]=1[C:9]([OH:17])=[C:8]1[C:3]([C:4](=[O:19])[CH:5]=[CH:6][C:7]1=[O:18])=[C:2]2[Cl:1])(=[O:21])[CH3:23]10-Chloro-8,9-dihydroxy-1,4-anthracenedione (compound 3) (180 mg) was dissolved with stirring in dry tetrahydrofuran (15 ml) at room temperature. Acetic anhydride (20 drops) and pyridine (15 drops) were added to the solution which was then stirred for 48 h. Acidified water was added and the suspension was extracted with dichloromethane. The combined organic layers were dried and evaporated, and the residue was column chromatographed on silica gel 60 (100 g) with chloroform/acetone mixture as the eluant. The major red band gave the product (compound 4) as a red solid (177 mg, 85%).
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