A mixture of 4-chloro-7-(2-chlorophenyl)-5,6,7,8-tetrahydroquinolin-5-one (0.1 g), aminoguanidine hydrochloride (0.040 g), concentrated hydrochloric acid (0.034 ml), water (0.034 ml) and ethanol (20 ml) was stirred at room temperature for 30 minutes and at 50° C. for 5 hours. Under reduced pressure, the solvent was evaporated, and the residue was dissolved in water. The solution was washed with ethyl acetate, and to the solution was added sodium hydrogen carbonate solution. The mixture was extracted with ethyl acetate, and the organic layer was washed with water and saturated brine, and dried with magnesium sulfate. Under reduced pressure, the solvent was evaporated, and the residue was purified with silica gel column chromatography (EtOAc/MeOH/Et3N). To the resulting two kinds of amorphous was added 1N hydrochloric acid and concentrated to give 7-(2-chlorophenyl)-4-ethoxy-5-guanidinoimino-5,6,7,8-tetrahydroquinoline hydrochloride (Compound 80) (0.05 g) as colorless crystals and 7-(2-chlorophenyl)-5-guanidinoimino-1,4,5,6,7,8-hexahydroquinoline-4-one hydrochloride (Compound 81) (0.04 g) as amorphous, respectively.
