(2S)-2-Amino-3-[4-(trifluoromethoxy)phenyl]propanoic acid hydrochloride (3 mg) prepared in Reference Example 3 (3b) was dissolved in 0.5 N sodium hydroxide (100 μL), and then (benzyloxy)carbonyl chloride (ZCl, 5 μL) was added thereto. The resulting mixture was stirred, and then water (100 μL) was added thereto. The resulting mixture was changed to acidic with 1 N hydrochloric acid (50 μL) and extracted with ethyl acetate (300 μL) to obtain the corresponding (2S)-2-{[(benzyloxy)carbonyl]amino}-3-[4-(trifluoromethoxy)phenyl]propanoic acid. The optical purity was determined by HPLC under the following conditions.
