To a mixture of 1-[(1R,2R)-2-(2,4-difluorophenyl)-2-hydroxy-1-methyl-3-(1H-1,2,4-triazol-1-yl)propyl]-3-[4-(1H-tetrazol-1-yl)phenyl]-2-imidazolidinone (0.80 g) and chloromethyl propanate (4.07 g) was added acetonitrile (1.6 ml), and the mixture was stirred for 10 hours at 100° C. under an argon atmosphere. The reaction mixture was concentrated under reduced pressure, and to the residue was added diisopropyl ether (8 ml). The resulting powder was collected by filtration. The powder was subjected to silica gel flush chromatography (eluent: ethyl acetate→acetone→acetone/ethanol=9/1→5/1), and the fraction containing the desired compound was concentrated under reduced pressure. The residue was subjected to ODS column chromatography (eluent: methanol/water=3/2). The eluate was concentrated in vacuo, and the residue was dissolved in water (10 ml). The solution was lyophilized to give 1-[(2R,3R)-2-(2,4-difluorophenyl)-2-hydroxy-3-[2-oxo-3-[4-(1H-tetrazol-1-yl)phenyl]-1-imidazolidinyl]butyl]-4-propanoyloxymethyl-1H-1,2,4-triazolium chloride (Compound 14, 0.04 g) as a white powder.
