F[C:2](F)(F)[C:3]([O:5][C:6]1[C:11]([F:12])=[C:10]([F:13])[C:9]([F:14])=[C:8]([F:15])[C:7]=1[F:16])=[O:4].[CH:19]1[C:31]2[CH:30]([CH2:32][O:33][C:34]([N:36]3[C:47]4[C:39](=[C:40]5[C:44](=[CH:45][CH:46]=4)[NH:43]C(C(O)=O)[CH2:41]5)[CH:38]=[CH:37]3)=[O:35])[C:29]3[C:24](=[CH:25][CH:26]=[CH:27][CH:28]=3)[C:23]=2[CH:22]=[CH:21][CH:20]=1.C(N(CC)CC)C>CN(C=O)C>[CH:28]1[C:29]2[CH:30]([CH2:32][O:33][C:34]([N:36]3[C:47]4[C:39](=[C:40]5[C:44](=[CH:45][CH:46]=4)[NH:43][CH:2]([C:3]([O:5][C:6]4[C:11]([F:12])=[C:10]([F:13])[C:9]([F:14])=[C:8]([F:15])[C:7]=4[F:16])=[O:4])[CH2:41]5)[CH:38]=[CH:37]3)=[O:35])[C:31]3[C:23](=[CH:22][CH:21]=[CH:20][CH:19]=3)[C:24]=2[CH:25]=[CH:26][CH:27]=1Pentafluorophenyl trifluoroacetate (0.3 mL, 1.75 mmol) was added to a solution of acid 9 (0.3 g, 0.7 mmol) and triethylamine (0.3 mL, 2.1 mmol) in 4 mL of anhydrous DMF. After 1 h DMF was evaporated and the residue chromatographed on silica eluting with 2% acetone in methylene chloride. Concentration of the pure product fraction and drying afforded 0.29 g (70%) of PFP ester 10 as a yellow solid.
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