1. N-Boc-L-3-(2-naphthyl)alanine (0.43 g, 2.0 mmol) was dissolved in a solvent mixture of dioxane (8 ml), water (8 ml) and triethylamine (4 ml).
2. BOC-ON (0.49 g, 2.0 mmol) was added and the reaction mixture was stirred overnight at room temperature under argon protection.
3. After completion of the reaction, water (30 ml) was added for dilution and extracted with ethyl acetate (3 x 20 ml).
4. The aqueous layer was acidified to pH=4 with 10% citric acid solution and extracted again with ethyl acetate (3 x 20 ml).
5. The organic phases were combined, dried over anhydrous magnesium sulfate and concentrated under reduced pressure to give a colorless oily product (0.52 g, 82% yield).
6. The product was characterized by 1H NMR (DMSO-d6): δ 7.8 (3H, m), 7.7 (1H, s), 7.4 (3H, m), 7.15 (1H, d), 4.2 (1H, m), 3.2 (1H, m), 2.9 (1H, m), 1.3 (9H, s).
