Benzyloxycarbonylglycine → (S)-4-benzyloxycarbonylaminoacetyl-3-(3-t-butoxycarbonylaminopropyl)-2-oxopiperazine-1-acetic acid t-butyl ester

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In a saturated aqueous solution of sodium hydrogencarbonate was dissolved (S)-3-(3-t-butoxycarbonylaminopropyl)-2-oxopiperazine-1-acetic acid t-butyl ester oxalate (1.6 g, 3.47 mmol). The solution was subjected to extraction with ethyl acetate, and the extract solution was concentrated under reduced pressure. The concentrate and N-Z-Gly-OH (0.87 g, 4.16 mmol) were dissolved in 16.0 cc of acetone. To the solution was added, at 15° C. under stirring, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (0.87 g, 4.51 mmol). The mixture was stirred for one hour at room temperature, and the reaction mixture was concentrated under reduced pressure. The concentrate was washed with a 5% aqueous solution of potassium hydrogensulfate and a saturated aqueous solution of sodium hydrogencarbonate. The organic layer was concentrated under reduced pressure, and the concentrate was purified by means of a silica gel column chromatography (ethyl acetate) to afford 1.95 g (100%) of the titled compound as a colorless amorphous powdery product.

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