[CH:1]1([C:6]([C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)([OH:16])[C:7]([O:9][CH:10]2[CH2:14][CH2:13][N:12]([CH3:15])[CH2:11]2)=[O:8])[CH2:5][CH2:4][CH2:3][CH2:2]1.[Br:23][CH2:24][C:25]([O:27][CH2:28][CH3:29])=[O:26].C(OCC)C>C(#N)C.C(Cl)CCl>[Br-:23].[CH:1]1([C:6]([C:17]2[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=2)([OH:16])[C:7]([O:9][CH:10]2[CH2:14][CH2:13][N+:12]([CH2:24][C:25]([O:27][CH2:28][CH3:29])=[O:26])([CH3:15])[CH2:11]2)=[O:8])[CH2:5][CH2:4][CH2:3][CH2:2]1To compound 4 (0.369 g, 122 mmol) in 10 ml of dry acetonitrile, ethyl bromoacetate (0.377 g, 2.25 mmol) was added at room temperature. The mixture was stirred for 2 h. Evaporation of acetonitrile gave a crude product. The crude product was dissolved in a small volume of ethylene chloride and then poured into 50 ml of dry ethyl ether to precipitate. This procedure was repeated three times to obtain Compound (b) as pure product (0.45 g, 79%). White powder, m.p.: 192-194° C.
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