Citric Acid → 5-(2-methoxyethoxy)-7-[methyl(2-thienylsulfonyl)amino]-1H-indole-2-carboxylic acid

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Reaction Steps

A mixture of ethyl 5-(2-methoxyethoxy)-7-[methyl(2-thienylsulfonyl)amino]-1H-indole-2-carboxylate (1.30 g), 1N aqueous sodium hydroxide solution (10 mL), tetrahydrofuran (10 mL) and ethanol (10 mL) was stirred at room temperature for 15 hr. The reaction mixture was acidified with aqueous citric acid solution, and extracted with ethyl acetate. The ethyl acetate layer was washed successively with water and saturated brine, dried (MgSO4), and concentrated to give the title compound (1.15 g, yield 93%) as colorless crystals. The crystals were recrystallized from ethyl acetate-hexane to give colorless prism crystals. melting point 198-199° C.

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