Diphenylphosphoryl azide (1.38 g) and triethylamine (0.77 ml) were added to a solution of isophthalic acid benzyl ester (1.15 g) in anhydrous dioxane (20 ml), the mixture was stirred at 60° C. for 30 minutes and subsequently stirred at internal temperature 80° C. for one hour. The reaction mixture was allowed to come to room temperature, a solution of (+)-1-tert-butylcarbonylmethyl-2-oxo-3-amino-5-phenyl-8-methyl-1,3,4,5-tetrahydro-2H-1,5-benzodiazepine (1.1 g) in anhydrous dioxane (20 ml) was added thereto, the mixture was stirred for 2 hours at room temperature. The resultant mixture was concentrated under reduced pressure, chloroform was added, the mixture was washed succesively with saturated aqueous sodium bicarbonate and saturated brine, and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure, the residue was purified by silica gel column chromatography(n-hexane:ethyl acetate=2:1), to thereby obtain 622 mg of the titled compound.
