Potassium Carbonate → [6-Chloro-2-(2-nitrobenzoyl)-1h-indol-3-yl]acetic acid

To a mixture of polymer-bound trans 4-chloro-2-(phenylsulfonylamino)cinnamate (step 1, 100 mg, 53 μmol) and 2-nitrophenacyl bromide (39 mg, 0.16 mmol) in acetone (3 ml) was added potassium carbonate (37 mg, 0.27 mmol). The mixture was agitated for 18 h. and filtrated. The residual resin was washed with water (20 ml×3), acetone (20 ml×3), dichloromethane (20 ml×3) and THF (20 ml×2) and dried. The resin was diluted with THF (4 ml) and then DBU was added (40 μl, 0.27 mmol). After agitating for 6 h, the resin was filtered off and washed with THF (20 ml×3), acetone (20 ml×3) and dichloromethane (20 ml×3). To the resin was added 95% trifluoroacetic acid in dichloromethane (5 ml) and the mixture was agitated for 3 h. The mixture was filtered and the residue was washed with dichloromethane (20 ml×5). The filtrate was concentrated and the residue was purified by HPLC (MeOH/AcONH4 aquous solution=60/40-90/10) to give 3.2 mg (17%) of the title compound.