N-(t-butyloxycarbonyl)-4-benzyloxy-L-phenylalanine (I) (3.71 g) was dissolved in dry tetrahydrofuran (100 ml) and, under ice cooling, triethylamine (1.5 ml) was added thereto. After stirring for 15 minutes, ethyl chlorocarbonate (1.10 g) was added, followed by stirring for 30 minutes. To this solution was added 3-aminopyridine (0.94 g) and the reaction was carried out at room temperature for 7 hours. The solid was filtered off and the filtrate was concentrated under reduced pressure. The residue was extracted with ethyl acetate. After a conventional post-treatment, N-(t-butyloxycarbonyl)-4-benzyloxy-L-phenylalanine 3-pyridylamide (II) (1.01 g) was obtained.
