[CH3:1][C@H:2]1[C@@H:19]([CH3:20])[N:6]2[C:7]3[CH:8]=[C:9]([C:14]([O:16]CC)=[O:15])[CH:10]=[CH:11][C:12]=3[CH:13]=[C:5]2[C:4](=[O:21])[NH:3]1.[OH-].[Na+].Cl>C(O)C>[CH3:1][C@H:2]1[C@@H:19]([CH3:20])[N:6]2[C:7]3[CH:8]=[C:9]([C:14]([OH:16])=[O:15])[CH:10]=[CH:11][C:12]=3[CH:13]=[C:5]2[C:4](=[O:21])[NH:3]1Ethyl (3S,4R)-3,4-dimethyl-1-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]indole-7-carboxylate (870 mg, 3.0 mmol) is suspended in ethanol (25 mL) and 1M NaOH solution (7.6 mL, 7.6 mmol) is added. The reaction mixture is heated at 80° C. for 1 h and then cooled to room temperature. The mixture is acidified with 1M HCl solution and ethanol is removed. The resulting solid is filtered, rinsed with water and dried to afford the title compound (760 mg, 97%).
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