C([O:5][C:6]([NH:8][CH2:9][C@H:10]([N:12]1[C:20]2[C:15](=[CH:16][CH:17]=[C:18]([C:21]([O:23][CH2:24][CH3:25])=[O:22])[CH:19]=2)[CH:14]=[C:13]1C(OCC)=O)[CH3:11])=O)(C)(C)C.C(O)(C(F)(F)F)=O.C([O-])([O-])=O.[K+].[K+]>C(Cl)Cl.C(O)C>[CH3:11][C@H:10]1[N:12]2[C:20]3[CH:19]=[C:18]([C:21]([O:23][CH2:24][CH3:25])=[O:22])[CH:17]=[CH:16][C:15]=3[CH:14]=[C:13]2[C:6](=[O:5])[NH:8][CH2:9]1
To a solution of diethyl 1-{(2R)-1-[(tert-butoxycarbonyl)amino]propan-2-yl}-1H-indole-2,6-dicarboxylate (2.7 g, 6.4 mmol) in CH2Cl2 (10 mL) is added TFA (10 mL). The reaction mixture is stirred for 2 h and the solvent is removed under vacuum. To a solution of the residue in ethanol (30 mL) is added K2CO3 (4.5 g, 32.3 mmol) and the reaction mixture is stirred at room temperature for 16 h. The solvent is evaporated and the residue is taken up in water. To the mixture is added a small amount of diethyl ether followed by heptanes (100 mL). The suspension is filtered to afford the title compound (1.3 g, 57% for two steps) as a solid.
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