To a solution of 2,6-dimethyl-4-[[[(1R)-1-(1-naphthalenyl)ethyl]amino]carbonyl]benzoic acid (Example 31; 100 mg, 0.29 mmol) in dichloromethane (1 mL) at 25° C. was added benzotriazol-1-yloxy-tris-(dimethylamino)-phosphonium hexafluorophosphate (BOP reagent, 140 mg, 0.32 mmol), 3-(thiophene-2-carbonyl)amino-L-alanine methyl ester HCl salt (Example 301; 114 mg, 0.43 mmol), followed by diisopropylethylamine (250 μL, 1.4 mmol) slowly dropwise. After stirring for 2 h, the reaction was diluted with ethyl acetate (50 mL) and washed with 1N HCl (10 mL), saturated aqueous sodium bicarbonate (10 mL) and brine (15 mL). The organic layer was dried (MgSO4), filtered, evaporated and flash chromatographed (silica, 50% ethyl acetate in petroleum ether) to give N-[2,6-dimethyl-4-[[[(1R)-1-(1-naphthalenyl)ethyl]amino]carbonyl]benzoyl]-3-(thiophene-2-carbonyl)amino-L-alanine methyl ester (88 mg, 54%) as an off-white solid.
