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 (25 mg, 0.0357 mmol), 2,6-di-tert-butyl-4-methyl pyridine (15.4 mg, 0.075 mmol), and dichloromethane (2 mL) was added trimethyloxonium tetrafluoroborate (11 mg, 0.075 mmol) and the mixture was stirred at room temperature for 21 hours. After confirming the consumption of the starting materials by LCMS, methanol and water were added. 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 (7 mg, 30% yield, white solid).
