To 70 mg (0.3 mmol) of 5-acetyl-4-hydroxy-3-methyl-benzofuran-2-carboxylic acid ethyl ester was added 115 mg (2 eq) EDCI, 109 mg (1 eq) of (S)-2-(4′-amino-biphenyl-4-sulfonylamino)-3-methyl-butyric acid methyl ester and 2 mL of DMF. The mixture was stirred at 65° C. overnight. The reaction mixture was poured into brine, and extracted with dichloromethane. The organic solution was washed with 2N HCl and water. Removal of the solvents under vacuum gave crude product, which was purified by column chromatography on silica gel to give 20 mg (10% yield) of (S)-2-{4′-[(5-acetyl-4-hydroxy-3-methyl-benzofuran-2-carbonyl)-amino]-biphenyl-4-sulfonylamino}-3-methyl-butyric acid methyl ester as a white solid.
