4-Methylmorpholine → N-benzyloxycarbonyl-3-(1-naphthyl)-L-alanyl-L-leucine ethyl ester

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3.49 g (10 mmole) of N-benzyloxycarbonyl-3-(1-naphthyl)-L-alanine and 1.21 g (12 mmole) of N-methylmorpholine were dissolved in 30 ml of anhydrous tetrahydrofuran, and then, whilst cooling the solution at -5° C., 1.30 g (12 mmole) of ethyl chlorocarbonate was added dropwise, with stirring, over a period of 15 minutes. 2.35 g (12 mmole) of L-leucine ethyl ester hydrochloride [which had been suspended in 10 ml of methylene chloride and neutralized with 1.21 g (12 mmole) of N-methylmorpholine] were added. The mixture was stirred for 2 hours with ice cooling, and then left standing overnight at room temperature. It was then condensed by evaporation under reduced pressure. Water was added to the residue, and the precipitating oily substance was extracted with ethyl acetate. The organic extract was washed with 1N hydrochloric acid, water, a 5% w/v aqueous solution of sodium bicarbonate and a saturated aqueous solution of sodium chloride, in that order, and then dried over anhydrous sodium sulfate. The solvent was distilled off under reduced pressure. The N-benzyloxycarbonyl-3-(1-naphthyl)-L-alanyl-L-leucine ethyl ester thus obtained in a syrupy form was dissolved in 30 ml of dimethylformamide, and 5.06 g (100 mmole) of hydrazine hydrate were added to the solution. The mixture was stirred for 36 hours at room temperature. The reaction product was then condensed by evaporation under reduced pressure, and water was added to the residue. The colorless crystals produced were collected by filtration, thoroughly washed with water and dried in a desiccator to yield 4.23 g of the title compound melting at 200°-204° C.

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