To a solution of 5-[3-chloro-4-(methylsulfonyl)phenyl]-6-[(2R,3R,7R)-2,3-diphenyl-1,4-dioxaspiro[4.4]non-7-yl]-1-{5-[(tetrahydro-2H-pyran-2-yloxy)methyl]-1,3-thiazol-2-yl}hexane-1,4-dione (416 mg) in acetic acid (2.5 mL) was added ammonium acetate (659 mg), and the mixture was stirred at 110° C. for 1 hr. After cooling to room temperature, the mixture was neutralized with saturated aqueous sodium hydrogen carbonate solution. The reaction mixture was diluted with ethyl acetate and washed with water. The ethyl acetate layer was dried (MgSO4) and concentrated. The residue was subjected to silica gel column chromatography, and the title compound (151 mg, yield 42%) was obtained as a pale-yellow amorphous solid from a fraction eluted with ethyl acetate-hexane (19:1, volume ratio). MS: 675 (MH+).
