[Cl:1][C:2]1[CH:3]=[C:4]([NH:10][C@H:11]([CH2:20][NH:21][S:22]([C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][C:26]=2[N+:31]([O-:33])=[O:32])(=[O:24])=[O:23])[CH2:12][C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH:5]=[CH:6][C:7]=1[C:8]#[N:9].[CH2:34](I)[CH3:35].C([O-])([O-])=O.[K+].[K+]>CN(C=O)C.O>[Cl:1][C:2]1[CH:3]=[C:4]([NH:10][C@H:11]([CH2:20][N:21]([CH2:34][CH3:35])[S:22]([C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][C:26]=2[N+:31]([O-:33])=[O:32])(=[O:23])=[O:24])[CH2:12][C:13]([O:15][C:16]([CH3:18])([CH3:19])[CH3:17])=[O:14])[CH:5]=[CH:6][C:7]=1[C:8]#[N:9]A mixture of the crude 1,1-dimethylethyl (3S)-3-[(3-chloro-4-cyanophenyl)amino]-4-{[(2-nitrophenyl)sulfonyl]amino}butanoate from the previous step, ethyl iodide (2.59 mL, 32.4 mmol) and K2CO3 (325 mesh, 6.71 g, 48.6 mmol) in DMF (93 mL) was stirred at room temperature for 60 min. The reaction was diluted with H2O (200 mL) and extracted with Et2O (3×). The organic extracts were washed with H2O (2×), dried over Na2SO4, filtered, and concentrated. The crude product was used directly in the next step.
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