N([O-])=O.[Na+].N[C@@H:6]([C:13]([OH:15])=[O:14])[CH2:7][C:8]1[N:12]=[CH:11][NH:10][CH:9]=1.[OH-].[NH4+].[ClH:18]>O>[Cl:18][C@H:6]([CH2:7][C:8]1[N:12]=[CH:11][NH:10][CH:9]=1)[C:13]([OH:15])=[O:14]A cold solution of sodium nitrite (2.63 g, 38 mmol) in water (5 ml) was added dropwise to a stirred suspension of D-histidine (2 g, 11.5 mmol) in concentrated hydrochloric acid (30 ml) at −5° C. The mixture was stirred at 0° C. for 1 hour and then at room temperature for 17 hours. The mixture was cooled and basified with aqueous ammonium hydroxide solution (2N) until pH=4-5. The solvent was then removed by evaporation under reduced pressure to afford (2R)-2-chloro-3-(1H-imidazol-4-yl)propanoic acid.
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