To a solution of benzyl 4-(3-indolyl)butyrate (33.70 g) in dichloromethane (400 ml) were added triethylamine (30 ml), 4-dimethylaminopyridine (1.22 g) and 3-nitrobenzoyl chloride (30.0 g). After refluxed for 16 hours, 3-nitrobenzoyl chloride (10.5 g) and triethylamine (5 ml) were added to the mixture. The mixture was allowed to reflux for 19 hours and 3-dimethylaminopropylamine (15 ml) was added at 0° C. The mixture was washed with diluted hydrochloric acid (200 ml ×2) and water (200 ml×4) and dried over magnesium sulfate. The solvent was removed in vacuo to give a solid of benzyl 4-[1-(3-nitrobenzoyl)indol-3-yl]butyrate (47.61 g).
