[C:1]([O:5][C:6]([N:8]1[CH2:13][CH:12]([C:14]([O:16][CH3:17])=[O:15])[CH2:11][CH:10]([C:18]([OH:20])=[O:19])[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].C1([C@H](N)C)C=CC=CC=1>C(O)C>[C:1]([O:5][C:6]([N:8]1[CH2:13][C@H:12]([C:14]([O:16][CH3:17])=[O:15])[CH2:11][C@H:10]([C:18]([OH:20])=[O:19])[CH2:9]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]A mixture of (3RS,5SR)-1-(tert-butoxycarbonyl)-5-(methoxycarbonyl)piperidine-3-carboxylic acid (6.16 g), (R)-(+)-1-phenylethylamine (2.60 g) and ethanol (24 ml) was dissolved by heating to 70° C., and recrystallized. The precipitated crystals were collected by filtration, dissolved in ethanol (7 ml) again and recrystallized. The precipitated crystals were collected by filtration, the obtained crystals were suspended in water, acidified by adding saturated aqueous potassium hydrogen sulfate solution, and the mixture was extracted 3 times with ethyl acetate. The extract was washed with saturated brine, and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure to give the object product (915 mg) as a powder.
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