[Cl:1][C:2]1[C:7]2[C:8](=[O:24])[N:9]3[CH2:23][CH2:22][CH2:21][C@H:10]3[C:11]3[N:12]([CH:13]=[N:14][C:15]=3[C:16]([O:18]CC)=[O:17])[C:6]=2[CH:5]=[CH:4][CH:3]=1.[OH-].[Na+].C(O)C>O>[Cl:1][C:2]1[C:7]2[C:8](=[O:24])[N:9]3[CH2:23][CH2:22][CH2:21][C@H:10]3[C:11]3[N:12]([CH:13]=[N:14][C:15]=3[C:16]([OH:18])=[O:17])[C:6]=2[CH:5]=[CH:4][CH:3]=115 g (43.4 mmol) of ethyl (S)-8-chloro-11,12,13,13a-tetrahydro-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-c][1,4]benzodiazepine-1-carboxylate and 1.85 g (46.3 mmol) of sodium hydroxide are treated with 60 ml of ethanol and 10 ml of water, the mixture is then heated to boiling under reflux for 45 minutes, the ethanol is subsequently distilled off in vacuo, the mixture remaining is treated with 46.5 ml of 1N hydrochloric acid and left to stand in an ice-bath for 2 hours. The precipitated material is filtered off under suction, washed with water and dried up to constant weight. There is obtained (S)-8-chloro-11,12,13,13a-tetrahydro-9-oxo-9H-imidazo[1,5-a]pyrrolo[2,1-c][1,4]benzodiazepine-1-carboxylic acid having a decomposition point of 265°.
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