To a solution of 2-(S)-tert-butoxycarbonylamino-pent-4-enoic acid (3.8 g, 18.0 mmol) and 2-(S)-amino-3-naphthalen-2-yl-propionic acid methyl ester (4.1 g, 18.0 mmol) in DMF (40 mL) are added 1-hydroxybenzotriazole (3.1 g, 23.4 mmol), N-methylmorpholine (9.1 g, 90.0 mmol) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (4.5 g, 23.4 mmol) consecutively and the reaction mixture is stirred for 3 hours. The reaction is quenched with aqueous NH4Cl and extracted with ethyl acetate. The extract is dried over Na2SO4, filtered and concentrated in vacuo and the residue purified over silica gel (hexanes/ethyl acetate, 1:1) to afford 6.4 g (84% yield) of the desired product.
