2-Amino-5-phenyl-(2s)-4-pentenoic acid → L-2-Amino-5-phenyl-pentanoic acid

L-Styryl alanine 1 (50 mg, 0.26 mmol) was dissolved in MeOH (5 mL) and the reaction vessel was flushed with nitrogen. Catalytic amount of palladium (10% on carbon) was added and the reaction vessel was placed under a hydrogen atmosphere. The mixture was stirred for 2 h at room temperature, then filtered over celite. The organic solvent was removed in vacuo to yield (S)-2-amino-5-phenyl-pentanoic acid 2 (51 mg, quant.) as a white powder: 1H-NMR (400 MHz, CD3OD) δ=7.42–7.25 (m, 5H), 3.71 (t, J=6.0, 1H), 2.69 (t, J=6.4, 2H), 1.85 (m, 2H), 1.70 (m, 2H). MS calcd. for C11H16NO2 (M+H+) 194.12. found 194.4. Step B: (S)-2-Amino-5-phenyl-pentanoic acid 2 (23 mg, 0.12 mmol) was dissolved in H2O (1 mL) containing equimolar amounts of NaOH (5 mg, 0.12 mmol). The solution was cooled to 0° C., then m-Toluic acid chloride (16 μL, 0.12 mmol) was added dropwise under vigorous stirring. The mixture was allowed to warm to room temperature and stirred for approx. 12 h. After acidification with 1 M HCl (1 mL), the product was extracted from the reaction mixture with DCM (4 mL). The organic layer was separated and the solvent was removed in vacuo to yield (S)-2-(3-methyl-benzoylamino)-5-phenyl-pentanoic acid 3 (21 mg, 56%) as a white solid: 1H-NMR (400 MHz, CD3OD) δ=7.83–7.09 (m, 9H), 4.62 (dd, J=5.0, J=9.1, 1H), 2.65 (m, 2H), 2.37 (s, 3H), 2.01–1.67 (m, 4H). MS calcd. for C19H22NO3 (M+H+) 312.16. found 312.4. Step C: (S)-2-(3-Methyl-benzoylamino)-5-phenyl-pentanoic acid 3 (21 mg, 0.07 mmol) was dissolved in DCM (2 mL), HOBt (20 mg, 0.14 mmol) and DIC (23 μL, 0.14 mmol) were added and the solution was stirred for 10 min at room temperature. N-(4-Methoxyphenyl)-ethane-1,2-diamine (24 mg, 0.14 mmol) was added and the solution was stirred for 3 h at room temperature. The solvent was removed in vacuo, and the remainder was purified by reverse HPLC to afford the title compound (S)-N-{1-[2-(4-Methoxy-phenylamino)-ethylcarbamoyl]-4-phenyl-butyl}-3-methyl-benzamide 4 (18 mg, 0.04 mmol, 56%) as a white solid: 1H-NMR (400 MHz, CD3OD) δ=7.56–7.48 (m, 2H), 7.36–7.16 (m, 7H), 6.96–6.87 (m, 4H), 4.48 (dd, J=6.2, J=13.7, 1H), 3.82 (s, 3H), 3.78–3.64 (m, 2H), 3.58–3.50 (m, 2H), 2.71–2.64 (m, 2H), 2.35 (s, 3H), 2.06–1.70 (m, 4H). MS calcd. for C28H34N3O3 (M+H+) 460.26. found 460.5.