[CH2:1]([O:3][C:4](=[O:17])[C:5]([C:7]1[CH:12]=[CH:11][C:10]([S:13]([CH3:16])(=[O:15])=[O:14])=[CH:9][CH:8]=1)=O)[CH3:2].[CH:18]1([O:23][NH2:24])[CH2:22][CH2:21][CH2:20][CH2:19]1>C(O)C>[CH2:1]([O:3][C:4](=[O:17])/[C:5](=[N:24]/[O:23][CH:18]1[CH2:22][CH2:21][CH2:20][CH2:19]1)/[C:7]1[CH:12]=[CH:11][C:10]([S:13]([CH3:16])(=[O:15])=[O:14])=[CH:9][CH:8]=1)[CH3:2](4-Methylsulfonyl-phenyl)-oxo-acetic acid ethyl ester (218 mg, 0.85 mmol) was stirred in ethanol (1.7 mL) and warmed in a 70° C. oil bath. O-Cyclopentyl-hydroxylamine (prepared as in Example 1, 146 mg, 1.06 mmol) was added. After 2 h, the reaction mixture was allowed to cool and concentrated in vacuo. Purification by flash column chromatography (Merck silica gel 60, 40-63 □m; 30% ethyl acetate/hexanes to 75% ethyl acetate/hexanes) afforded (E)-cyclopentyloxyimino-(4-methanesulfonyl-phenyl)-acetic acid ethyl ester (60 mg, 21%) as a clear, colorless film containing an unidentified impurity: LC-MS (ESI) m/e calcd for C16H21NO5S [M+] 339.11, found 340 [M+H+].
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