About 2 g of 1-(2-Hydroxyethyl)-3,3-dimethylindolino-6′-nitrobenzopyrylospiran (TCI America), about 0.44 ml of triethylamine, and about 0.69 g of 4-(dimethylamino)pyridine were dissolved in about 30 ml of dichloromethane. After addition of about 0.59 g of succinic anhydride, the solution was stirred under Ar at room temperature for about 19 hours. The mixture was washed with 5% aqueous hydrochloric acid, aqueous sodium bicarbonate, and water, then dried over magnesium sulfate. After the solvent was distilled off, the concentrated solution was added dropwise to hexane under stirring. The resulting solid was collected by filtration to yield 4-(2-(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indoline]-1′-yl)ethoxy)-4-oxobutanoic acid.
