1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide (214 g, 1.12 mmol) was added to a solution of benzofuran-2-carboxylic acid (166 g, 1.02 mmol), (S)-2-({1-[(2R,5S)-5-((S)-2-Amino-4-methyl-pentanoylamino)-2-methyl-6-hydroxy-azepan-1-yl]-methanoyl}-amino)-4-methyl-pentanoic acid methyl ester (430 mg, 0.93 mmol), diisopropylethylamine (240 mg, 0.32 ml, 1.86 mmol), hydroxybenztriazole (151 mg, 1.12 mmol) in DMF (5 ml) and was stirred at RT overnight. The reaction mixture was stirred overnight. The reaction mixture was diluted with EtOAc (30 ml), washed with cold aq. 1N HCl, aq. sat. NaHCO3, and brine, and then dried with magnesium sulfate, filtered, concentrated in vacuo by rotary evaporation, and chromatographed (silica gel, 2% to 3% MeOH/CH2Cl2) to yield the title compound (478 mg, 84% for two steps): electrospray MS: 572.4
