C(OC([NH:8][CH2:9][CH2:10][C@@H:11]([N:13]1[C:21]2[C:16](=[CH:17][CH:18]=[C:19]([C:22]([O:24][CH2:25][CH3:26])=[O:23])[CH:20]=2)[CH:15]=[C:14]1[C:27](OCC)=[O:28])[CH3:12])=O)(C)(C)C.C(O)(C(F)(F)F)=O.C([O-])([O-])=O.[K+].[K+].CCOC(C)=O>C(Cl)Cl.C(O)C>[CH3:12][C@@H:11]1[N:13]2[C:21]3[CH:20]=[C:19]([C:22]([O:24][CH2:25][CH3:26])=[O:23])[CH:18]=[CH:17][C:16]=3[CH:15]=[C:14]2[C:27](=[O:28])[NH:8][CH2:9][CH2:10]1To a solution of diethyl 1-{(2S)-4-[(tert-butoxycarbonyl)amino]butan-2-yl}-1H-indole-2,6-dicarboxylate (891 mg, 2.1 mmol) in CH2Cl2 (4 mL) is added TFA (3 mL). The mixture is stirred at room temperature for 1 h then the solvent is evaporated. To a solution of the residue in ethanol (10 mL) is added K2CO3 (854 mg, 6.2 mmol). The reaction mixture is refluxed for 4 h with vigorous stifling. EtOAc is added and the organic layer is washed with water, brine, dried (MgSO4) and concentrated to afford crude compound which is purified by flash column chromatography using EtOAc in hexanes then methanol in CH2Cl2 to afford the title compound (269 mg, 46%).
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