Diisopropylethylamine → 4-[(2-chloro-5-cyanophenylcarbonyl)amino]-N-[[1-(2-methoxy-ethyl)cyclopentyl]carbonyl]-L-phenylalanine methyl ester

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To a solution of 4-[(2-chloro-5-cyanophenylcarbonyl)amino]-L-phenylalanine methyl ester TFA salt (0.55 mmol, 0.35 g), HBTU (0.65 mmol, 0.24 g) and 1-(2-methoxyethyl)cyclopentane carboxylic acid (0.65 mmol, 0.11 g) in DMF (3 mL) was added diisopropylethylamine (1.65 mmol, 0.29 mL) at room temperature. The clear solution was stirred for 15 h at room temperature and diluted with 50 mL of ethyl acetate. Then, the ethyl acetate layer was washed successively with 0.5N hydrochloric acid (2×20 mL), saturated sodium bicarbonate solution (2×20 mL) and brine solution and was dried over anhydrous magnesium sulfate. Filtration of the drying agent and concentration of the solvent gave a crude product which was purified by silica gel column chromatography to afford 0.25 g (87%) of a white solid: mp 172-175° C. HR MS (C27H30ClN3O5): Obs mass, 512.1949. Calcd mass, 512.1953 (M+H).

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