[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([C:14]2[C:23](Cl)=[N:22][C:21]3[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=3)[N:15]=2)[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[OH-:25].[Na+].[Cl-].[Na+]>C(OC)(C)(C)C.O.CS(C)=O>[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([C:14]2[C:23](=[O:25])[NH:22][C:21]3[C:16](=[CH:17][CH:18]=[CH:19][CH:20]=3)[N:15]=2)[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]4-(3-Chloro-quinoxalin-2-yl)-piperazine-1-carboxylic acid tert-butyl ester (10.0 g, 28.7 mmol; from Step 1) was added to a mixture of sodium hydroxide (40 g), water (40 g) and DMSO (40 g) at 100° C. After being stirred for 1 h at this temperature, water (200 g) and methyl tert-butyl ether (1000 g) and sodium chloride (50 g) were added. The crystals formed from the organic layer were collected by filtration and dried. This furnished 4.0 g (42%) of the title compound as white crystals. 1H NMR analysis supports the stated structure.
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