7-Nitro-1H-indole-2-carboxylic acid (8.2 g, 22.7 mmol) prepared in Step A and 2,2-dimethyl-propionic acid (R)-2-amino-3-(4-methoxy-benzylsulfanyl)-propyl ester (13.2 g, 27.2 mmol) prepared in Preparation 31 were dissolved in N,N-dimethylformamide (100 mL). EDC (6.6 g, 25.0 mmol) and HOBT (4.6 g, 25.0 mmol) were added thereto, and the mixture was stirred for 8 h at room temperature. Saturated aqueous sodium bicarbonate solution was added to the mixture to quench the reaction. The reaction mixture was extracted with ethyl acetate, dried over anhydrous magnesium sulfate, filtered, and distilled under reduced pressure. The residue was purified by column chromatography to give the title compound (8.1 g, Yield 71%).
