Triethylamine (0.22 mL) was added to a solution of 3-carbamoyl-1-cyclopropyl-4-ethoxy-1H-indole-6-carboxylic acid (229 mg), 3-(4-oxo-spiro[chroman-2,4′-piperidin]-6-yl)benzoic acid methyl ester hydrochloride (306 mg), WSC hydrochloride (166 mg) and HOBT (133 mg) in DMF (4 mL), and the mixture was stirred at 60° C. for 1 hour. After cooling to room temperature, the reaction mixture was diluted with ethyl acetate, then washed successively with water, aqueous saturated sodium bicarbonate and saturated saline water. The organic layer was dried over sodium sulfate, filtered, concentrated, and purified through silica gel column chromatography (chloroform/methanol) to obtain the intended ester derivative as a colorless amorphous substance. 1H-NMR (400 MHz, CDCl3) δ: 8.71 (1H, s), 8.25 (1H, dd, J=1.5, 1.5 Hz), 8.14 (1H, d, J=2.4 Hz), 8.04-8.00 (2H, m), 7.83-7.74 (2H, m), 7.51 (1H, dd, J=7.8, 7.8 Hz), 7.37 (1H, d, J=1.5 Hz), 7.13 (1H, d, J=7.8 Hz), 6.74 (1H, d, J=1.5 Hz), 5.54 (1H, s), 4.62-4.41 (1H, br m), 4.29 (2H, q, J=7.0 Hz), 3.95 (3H, s), 2.28-1.71 (4H, br m), 3.88-3.32 (4H, br m), 2.82 (2H, s), 1.55 (3H, t, J=7.0 Hz), 1.16-1.00 (4H, m); MS [M+H]+=622.
