60% Sodium hydride in mineral oil (0.13 g) was added to a solution of 4-[3-(3-tert-butoxycarbonylaminobenzoyl)-indol-1-yl]butyric acid (0.47 g) in N,N-dimethylformamide (7 ml). The mixture was stirred at 0° C. for 1 hour. Benzyl bromide (0.95 g) was added to the mixture and the mixture was stirred at room temperature for 20 hours. The mixture was poured into ice water and 0.5N-hydrochloric acid and extracted with ethyl acetate. The organic layer was washed with water, dried over magnesium sulfate and evaporated. The residue was chromatographed on silica gel (30 g) eluting with a mixture of n-hexane and ethyl acetate (5:1) to give benzyl 4-[3-[3-(N-benzyl-N-tert-butoxycarbonylamino)benzoyl]indol-1-yl]butyrate (325 mg) as an oil.
