A mixture of 2-[4-(benzyloxycarbonyl)piperazin-1-yl]-4-[(1S,4R)-(4-hydroxycyclopent-2-en-1-yl)oxy]quinazoline (1.30 g), a solution of osmium tetroxide in t-butanol (osmium tetroxide 252 mg/t-butanol 18.1 g) (532 mg) and 4-methylmorpholine N-oxide (375 mg) in water (3 ml)--acetone (25 ml) is stirred at room temperature for 17 hours. Acetone is distilled off from the reaction mixture under reduced pressure, and to the resultant is added ethyl acetate, and the mixture is washed with 10% aqueous sodium sulfite solution and water. The ethyl acetate solution is dried over anhydrous magnesium sulfate and evaporated to dryness under reduced pressure, and the residue is purified by medium pressure liquid column chromatography (eluent, chloroform:methanol=50:1, 10:1, v/v) to give 2-[4-(benzyloxycarbonyl) piperazin-1-yl]-4-[(1S,2S,3S,4R)-(2,3,4-trihydroxycyclopentan-1-yl)oxy]quinazoline (1.05 mg) as foam.
