To a solution of 4-[1-(3-aminobenzoyl)indol-3-yl]butyric acid (1.0 g) and diisopropylethylamine (1.3 g) in carbon tetrachloride (20 ml) was added bis(4-chlorophenyl)methyl chloride (0.84 g). The mixture was refluxed for 6 hours and the solvent was removed in vacuo. The residue was dissolved in ethyl acetate (20 ml) and diluted hydrochloric acid (30 ml) and washed with water (30 ml×3). The solution was dried over magnesium sulfate and the solvent was removed in vacuo. The residue was purified by a column of silica gel to give a yellow solid of 4-[1-[3-[bis(4-chlorophenyl)methylamino]benzoyl]indol-3-yl]butyric acid (1.19 g).
