Aqueous 1N NaOH (11.6 ml, 11.6 mmol) was added to a stirred solution of methyl 4′-({6-(5-carbamoylpyridin-2-yl)-4-oxospiro[chroman-2,4′-piperidin]-1′-yl}carbonyl)-2′,6′-diethoxybiphenyl-4-carboxylate (3.85 g, 5.80 mmol) in THF (40 ml)-MeOH (40 ml) and the mixture was stirred at room temperature for 12 days. After water was added to the mixture, the organic solvents were evaporated under reduced pressure. The aqueous residue was purified by ODS column chromatography eluting with H2O/MeOH and the residue was crystallized from MeOH to give intended compound as a pale red solid. The solid was diluted in H2O and aqueous 1N NaOH, and was purified by ODS column chromatography eluting with H2O/MeOH, and the residue was crystallized from MeOH to give intended compound (2.04 g, 3.04 mmol, 52.4% yield) as a pale red crystal.
