To a solution of 3-[carboxymethyl-(4-chloro-benzyl)-amino]-pyrrolidine-1-carboxylic acid tert-butyl ester (0.48 g, 1.30 mmol) in tetrahydrofuran (10 mL) was added EDCI (0.39 g, 1.95 mmol), HOBT (0.26 g, 1.95 mmol), and stirred for 30 min., followed by the addition of N-methyl morpholine (0.43 mL, 3.90 mmol) and N-ethyl amine (0.1 mL, 1.95 mmol). The reaction mixture was stirred at room temperature for 18 h. Upon concentration, the residue was dissolved in ethyl acetate and washed with saturated aqueous sodium bicarbonate. The combined organics were washed with brine and dried over sodium sulfate. The crude product was purified on silica using gradient elution from hexane/ethyl acetate (50%) to ethyl acetate (100%).
