To a mixture of No. 5217614, tert-butyl (E)-(2S,3S)-3-[(S)-2-(4-but-2-ynyloxy-phenyl)-1-methoxycarbonyl-ethylcarbamoyl]-2-hydroxy-2-(2-hydroxy-ethyl)-12-oxo-nonadec-4-enoate (150 mg, 0.214 mmol) and dichloromethane (15 mL) were added trifluoroacetic acid anhydride (36 μL, 0.258 mmol), triethylamine (89 μL, 0.642 mmol), and DMAP (1.3 mg, 0.0107 mmol), and the mixture was stirred at room temperature. After being stirred for 3 hours, trifluoroacetic acid anhydride (72 μL, 0.516 mmol) was added again. After confirming the consumption of No. 5217614 by LCMS, formic acid (5.0 mL) was added and the mixture was stirred overnight. The solvent was distilled off under reduced pressure to obtain (E)-(2S,3S)-3-[(S)-2-(4-but-2-ynyloxy-phenyl)-1-methoxycarbonyl-ethylcarbamoyl]-2-hydroxy-12-oxo-2-[2-(2,2,2-trifluoro-acetoxy)-ethyl]-nonadec-4-enoic acid (ESI (LC/MS positive mode) m/z 740 (M+H); Rt 2.64 min.). To the obtained (E)-(2S,3S)-3-[(S)-2-(4-but-2-ynyloxy-phenyl)-1-methoxycarbonyl-ethylcarbamoyl]-2-hydroxy-12-oxo-2-[2-(2,2,2-trifluoro-acetoxy)-ethyl]-nonadec-4-enoic acid (16 mg, 0.0216 mmol) were added toluene (3.0 mL), methanol (1.0 mL), and trimethylsilyldiazomethane (0.6 M in n-hexane, 54 μL, 0.0324 mmol), and the mixture was stirred at room temperature. After being stirred for 1.5 hours, trimethylsilyldiazomethane (0.6 M in n-hexane, 54 μL, 0.0324 mmol) was added. After stirring for 1 hour, the organic solvent was distilled off under reduced pressure. The resulting residue was purified by preparative HPLC and then freeze-dried to obtain the title compound (17 mg, 99% yield, white solid).
