To a solution of cyclopropyl-2-(2-nitro-benzenesulfonylamino)-propionic acid (7.74 mmol) in DMF (10 mL) are added 2-(S)-amino-3-naphthalen-2-yl-propionic acid methyl ester (3.1 g, 11.7 mmol), N-methylmorpholine (4.67 g, 46.27 mmol), 1-hydroxybenzotriazole (17.76 mmol) and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (1.93 g, 10.07 mmol) consecutively. The resulting mixture is stirred for 4 hours, quenched with aqueous NH4Cl and extracted with ethyl acetate. The combined extracts are dried over Na2SO4, filtered and concentrated in vacuo. The residue is purified over silica gel (hexanes/ethyl acetate, 1:1) to afford 3.46 g (85% yield) of the desired product. 1H NMR (300 MHz, CDCl3) δ 8.04 (dd, J=7.7, 1.4 Hz, 1H), 7.42–7.68 (m, 9H), 7.24 (dd, J=8.4, 1.5 Hz, 1H), 6.94 (d, J=8.1 Hz, 1H), 6.20 (d, J=6.9 Hz, 1H), 4.84–4.96 (m, 1H), 3.98–4.07 (m, 1H), 3.71 (s, 3H), 3.29 (dd, J=14.0, 5.6 Hz, 1H), 3.14 (dd, J=14.0, 7.4 Hz, 1H), 1.62–1.72 (m, 1H), 1.23–1.42 (m, 1H), 0.02–0.40 (m, 3H), −0.14–0.02(, 2H); 13C NMR (75 MHz, CDCl3) δ 171.74, 170.45, 147.91, 134.02, 133.73, 133.61, 133.18, 132.70, 131.07, 128.55, 128.32, 127.89, 127.41, 126.54, 126.12, 125.76, 58.59, 53.56, 52.74, 38.34, 37.55, 6.86, 4.38; MS (ESMS) m/z 526.1 (M+H)+.
