After dissolving 245 mg of 3-[3-(2-fluorophenoxymethyl)pyrrolidino]methyl-2-methoxypyrazine in 5 ml of ethanol, 15 ml of 4N hydrogen chloride/ethyl acetate was added, and the mixture was heated to reflux for 8 hours and then stirred overnight at 60° C. Aqueous sodium bicarbonate solution was added to the reaction solution and extraction was performed with ethyl acetate. The organic layer was washed with water and saturated brine in that order and dried over anhydrous magnesium sulfate, and then the solvent was distilled off under reduced pressure. The residue was purified by NH silica gel column chromatography (solvent: ethyl acetate/methanol). This was dissolved in a small amount of ethanol, and then 47 mg of oxalic acid anhydrous and ethyl acetate were added and the precipitate was filtered out to obtain the title compound (171 mg, 56% yield).
