48% hydrobromic acid (1.7 mL) was added to a solution of 3-(6-{(E)-1-(4-tert-butylphenyl)-2-[(2R)-1-(2,4-dimethoxybenzyl)-5-oxopyrrolidin-2-yl]ethenyl}-2-methoxypyridin-3-yl)propanoic acid (172 mg) in 1,4-dioxane (1.7 mL), and the mixture was stirred at 65° C. for two hours. Water was added to the reaction solution, followed by extraction with ethyl acetate. The organic layer was washed with brine and dried over anhydrous magnesium sulfate, after which the solvent was evaporated under reduced pressure. The resulting residue was purified by silica gel column chromatography (chloroform:methanol=10:0→9:1) to give 3-(6-{(E)-1-(4-tert-butylphenyl)-2-[(2R)-1-(2,4-dimethoxybenzyl)-5-oxopyrrolidin-2-yl]ethenyl}-2-oxo-1,2-dihydropyridin-3-yl)propanoic acid as a yellow oil (153 mg).
