[CH:1]1([NH:7][C:8]2[CH:13]=[CH:12][C:11]([S:14]([NH2:17])(=[O:16])=[O:15])=[CH:10][C:9]=2[N+:18]([O-:20])=[O:19])[CH2:6][CH2:5][CH2:4][CH2:3][CH2:2]1.[Br:21]N1C(C)(C)C(=O)N(Br)C1=O.FC(F)(F)C(O)=O.C([O-])(O)=O.[Na+]>ClCCl>[Br:21][C:13]1[CH:12]=[C:11]([S:14]([NH2:17])(=[O:16])=[O:15])[CH:10]=[C:9]([N+:18]([O-:20])=[O:19])[C:8]=1[NH:7][CH:1]1[CH2:2][CH2:3][CH2:4][CH2:5][CH2:6]1A room temperature solution of Example 3A (1.81 g, 6.0 mmol) and 1,3-dibromo-5,5-dimethylhydantoin (950 mg, 3.3 mmol) in dichloromethane was treated with trifluoracetic acid (796 uL, 9.0 mmol), stirred in darkness for 18 hours, treated with saturated NaHCO3, and extracted with diethyl ether. The combined extracts were washed with brine, dried (Na2SO4), and concentrated. The concentrate was purified by flash column chromatography on silica gel with 15% ethyl acetate/hexanes to provide the desired product. MS (ESI(−)) m/e 376 (M−H)−.
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