Cl[C:2]([O:4][CH2:5][CH3:6])=[O:3].O.Cl.[NH2:9][N:10]=[CH:11][C:12]1[CH:13]=[C:14]2[C:18](=[CH:19][CH:20]=1)[NH:17][CH:16]=[C:15]2[CH2:21][CH2:22][NH:23][C:24](=[O:33])[O:25][CH2:26][C:27]1[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=1.C(N(C(C)C)CC)(C)C>O1CCCC1>[CH2:5]([O:4][C:2]([NH:9][N:10]=[CH:11][C:12]1[CH:13]=[C:14]2[C:18](=[CH:19][CH:20]=1)[NH:17][CH:16]=[C:15]2[CH2:21][CH2:22][NH:23][C:24](=[O:33])[O:25][CH2:26][C:27]1[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=1)=[O:3])[CH3:6]Ethyl chloroformate (0.44 ml) was added slowly to a suspension of the product of Stage (ii) (0.8 g) and diisopropylethylamine (1.0 ml) in freshly distilled tetrahydrofuran (50 ml). The mixture was stirred at room temperature for 24 h and then reduced to dryness. The residue was chromatographed on silica (D) to give the title compound as an oil (0.4 g). T.l.c. SiO2 : ethyl acetate, Rf. 0.80 (Ceric).
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