Ammonia → (R)-diethyl 2-t-butyloxycarbonylamino-2-carbamoylsuccinate

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Reaction Steps

A solution of (R)-1-ethyl hydrogen 3-t-butyloxycarbonylamino-3-ethoxycarbonylsuccinate (1.0 g) obtained in Example 14 in THF (20 mL) was added with triethylamine (0.62 mL) and isobutyl chloroformate (0.55 mL, 0.57 g) in this order at −15° C. with stirring, and the mixture was stirred for 30 minutes. A solution of 25% aqueous ammonia (0.30 mL) was dropped into the reaction mixture at the same temperature. The reaction mixture was stirred at the same temperature for 30 minutes, and then poured into diluted hydrochloric acid, the mixture was extracted with ethyl acetate, and then the extract was dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure, and the residue was subjected to silica gel column chromatography, in which elution was performed with n-hexane/ethyl acetate (1:1) for purification, and then crystallized from ethyl acetate/n-hexane to obtain the title compound (0.67 g, yield: 73%) as colorless crystals. Optical rotation [α]D22 was +2.74° (c 0.50, ethanol).

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