Reaction SMILES: [OH:1][C:2]([CH2:12][C:13]1[C:21]2[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=2)[NH:15][CH:14]=1)([C:9]([OH:11])=[O:10])[CH2:3][C:4](=O)[C:5]([OH:7])=[O:6].N1C2C(=CC=CC=2)C(CC(=O)C(O)=O)=C1.[OH:37][NH2:38].[OH-].[Na+].Cl>>[OH:1][C:2]([CH2:12][C:13]1[C:21]2[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=2)[NH:15][CH:14]=1)([C:9]([OH:11])=[O:10])[CH2:3][C:4](=[N:38][OH:37])[C:5]([OH:7])=[O:6]
Reactant: NO
Reactant: O=C(O)C(=O)CC(O)(Cc1c[nH]c2ccccc12)C(=O)O
Agent: Cl
Agent: O=C(O)C(=O)Cc1c[nH]c2ccccc12
Agent: [Na+]
Product: O=C(O)C(CC(O)(Cc1c[nH]c2ccccc12)C(=O)O)=NO
Temperature: 25 °C
Reaction time: 8 h

Procedure:
To a solution of aldol reaction containing 4-hydroxy-4-(3-indolylmethyl)-2-ketoglutaric acid is added an excess amount (about 4 equimolar amount for the used amount of indole-3-pyruvic acid) of hydroxyamine, and the mixture was adjusted to pH 7.0 to 10.0 by addition of 2N sodium hydroxide aqueous solution or 1N hydrochloric acid. 2) The mixture was stirred at room temperature overnight to form 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid. 3) A portion of the resulting reaction mixture was weighed and diluted with pure water in a mess-flask so that the concentration of 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid became 100 to 150 ppm; thus a sample for analysis was prepared. Method of Determination of the Yield 4) The sample for analysis prepared in the above item 3) was applied to the following high performance liquid chromatography, and the yield was calculated by comparison in the percentage of the area of sample to that of a standard solution of 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid; thus, the yield (%) from indole-3-pyruvic acid used was calculated. Analytical condition for high performance liquid chromatography (gradient) Column: CAPCELL PAK C18 (MGII) 5 μm 4.6 mm×250 mm Column temperature: 25° C. Wavelength for detection: 210 nm Flow rate: 1.0 ml/min Mobile phase composition: Solution A: KH2PO4 (20 mM)+K2HPO4 (20 mM) aqueous solution/acetonitrile=100/5 Solution B: KH2PO4 (20 mM)+K2HPO4 (20 mM) aqueous solution/acetonitrile=1/1 Injected amount of sample: 10 μL Retention time: 11 minutes (4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid) Method of Determination of Enantiomeric Excess 5) The sample for analysis mentioned in the above item 3) was applied to the following high performance liquid chromatography, and on the basis of the peak integral value derived from the enantiomer at the 4 position of 4-hydroxy-4-(3-indolylmethyl)-2-hydroxyiminoglutaric acid, the selectivity and enantiomeric excess (% ee) of the enantiomer at the 4 position were calculated by the following procedure from the following equation: Enantiomeric excess of the enantiomer at 4 =(Peak area of 4S-isomer−Peak area of 4R isomer)/(Peak area of 4S-isomer+Peak area of 4R isomer)×100 (Regarded as % ee4S when the Sign is +, and % ee4R when the Sign is −) Analytical condition for high performance liquid chromatography (gradient) Column: SUMICHIRAL OA7100 4.6 mm×250 mm Column temperature: 10° C. Wavelength for detection: 210 nm Flow rate: 0.5 ml/min Mobile phase composition: Solution A: KH2PO4 (20 mM)+K2HPO4 (20 mM) aqueous solution/acetonitrile=100/5 Solution B: KH2PO4 (20 mM)+K2HPO4 (20 mM) aqueous solution/acetonitrile=1/1 Injected amount of sample: 10 μL Retention time: 19 min for 4R isomer; 21 min for 4S isomer