[OH:1][C:2]([CH2:13][C:14]1[C:22]2[C:17](=[CH:18][CH:19]=[CH:20][CH:21]=2)[NH:16][CH:15]=1)([C:10]([OH:12])=[O:11])[CH2:3][C:4](=[N:8][OH:9])[C:5]([OH:7])=[O:6].Cl.O.[NH3:25]>C(O)C>[NH4+:8].[NH4+:25].[OH:1][C:2]([CH2:13][C:14]1[C:22]2[C:17](=[CH:18][CH:19]=[CH:20][CH:21]=2)[NH:16][CH:15]=1)([C:10]([O-:12])=[O:11])[CH2:3][C:4](=[N:8][OH:9])[C:5]([O-:7])=[O:6]The above experiment in Example 2 was carried out on a 24-fold scale to prepare an aldol reaction mixture containing 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid. The resulting aldol reaction mixture was adjusted to pH 1.2 by addition of 12N hydrochloric acid and extracted twice with ethyl acetate (100 ml×2). The organic layer was washed with saturated brine, dried with anhydrous magnesium sulfate, filtered to remove the magnesium sulfate, and concentrated with an evaporator to yield the residue. 28% Ammonia water (20 ml) was added, and then 200 ml of ethanol was added, and the mixture was preserved at 5° C. for 3 days. The precipitated crystals were collected by filtration and dried under reduced pressure to yield 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid diammonium salt (2.2 g)(purity 88%; yield 23%). The selectivity for the enantiomer was 44% ee for the 4R isomer.
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