C[O:2][C:3]([C:5]1[NH:6][C:7]2[C:12]([CH:13]=1)=[CH:11][CH:10]=[C:9]([N+:14]([O-:16])=[O:15])[CH:8]=2)=[O:4].[OH-].[Na+]>CO>[N+:14]([C:9]1[CH:8]=[C:7]2[C:12]([CH:13]=[C:5]([C:3]([OH:4])=[O:2])[NH:6]2)=[CH:11][CH:10]=1)([O-:16])=[O:15]4.4 g (20 mmol) 6-Nitro-1H-indole-2-carboxylic acid methyl ester (190) was dissolved in 80 mL methanol and was treated with 30 mL 1M NaOH overnight at 55 C°. The methanol was evaporated, the remaining aqueous solution was diluted to 100 mL and was acidified to pH 2 using concentrated HCl. The precipitate was filtered off, washed three times with water then dried to give 3.92 g (95%) 191 as yellow powder. The NMR was consistent with the structure. 191 was used without further purification.
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