[CH2:1]([O:3][C:4]([N:6]1[CH2:14][CH2:13][CH:12]2[CH:8]([CH2:9][C:10]3[CH:17]=[CH:16][S:15][C:11]=32)[CH2:7]1)=[O:5])[CH3:2].C(Cl)(Cl)Cl.C1C(=O)N([Br:29])C(=O)C1>CC(O)=O>[CH2:1]([O:3][C:4]([N:6]1[CH2:14][CH2:13][CH:12]2[CH:8]([CH2:9][C:10]3[CH:17]=[C:16]([Br:29])[S:15][C:11]=32)[CH2:7]1)=[O:5])[CH3:2]A solution of the product from step h) (722 mg, 2.88 mmol) in AcOH (7.2 ml) and CHCl3 (7.2 ml) was treated with NBS (529 mg, 2.97 mmol) at 22° C. for 30 minutes. Next, the reaction was carefully quenched with sat. NaHCO3 (10 ml), extracted with EtOAc (2×75 ml) and the combined organic extracts were dried (MgSO4) and solvent evaporated in vacuo leaving the crude product that was purified by silica-gel chromatography using a ethyl acetate/hexanes gradient (10% to 50% ethyl acetate) to give the subtitle compound. MS calculated for C15H20BrNO2S+H 358, observed M-tBu 302, 304.
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