Cl.CCOC(C)=O.C(OC([NH:15][NH:16][C:17](=[O:49])[C:18]1[CH:23]=[CH:22][C:21]([O:24][CH2:25][C:26]2[CH:35]=[CH:34][C:33]3[C:28](=[CH:29][CH:30]=[CH:31][CH:32]=3)[N:27]=2)=[CH:20][C:19]=1[C:36]1([C:43]2[CH:48]=[CH:47][CH:46]=[CH:45][CH:44]=2)[CH2:41][CH:40]2[CH2:42][CH:37]1[CH2:38][CH2:39]2)=O)(C)(C)C>C(Cl)Cl>[C:43]1([C:36]2([C:19]3[CH:20]=[C:21]([O:24][CH2:25][C:26]4[CH:35]=[CH:34][C:33]5[C:28](=[CH:29][CH:30]=[CH:31][CH:32]=5)[N:27]=4)[CH:22]=[CH:23][C:18]=3[C:17]([NH:16][NH2:15])=[O:49])[CH2:41][CH:40]3[CH2:42][CH:37]2[CH2:38][CH2:39]3)[CH:44]=[CH:45][CH:46]=[CH:47][CH:48]=1Cold hydrogen chloride/EtOAc (10 mL; saturated solution) was added to a stirred solution of 4c (0.99 g, 1.76 mmol) in methylene chloride (5 mL) at room temperature. After approximately 1 h, the reaction mixture was concentrated in vacuo and the crude residue partitioned between saturated aqueous sodium bicarbonate and methylene chloride. The organic phase was separated, and the aqueous phase was re-extracted twice with methylene chloride. The combined organic extracts were washed with brine, dried (Na2SO4) and concentrated in vacuo to afford 4d as a white powder (m/z (ES) 464 (MH)+) which was used without further purification in the subsequent reaction.
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