Reaction Steps
L-Styryl alanine 1 (50 mg, 0.26 mmol) was dissolved in MeOH (5 mL) and placed into a Parr-hydrogenation apparatus. Catalytic amounts of rhodium (5% on Al2O3) were added and the reaction vessel was placed under a hydrogen at 55 psi. The mixture was shaken for 20 h at room temperature, then filtered over celite. The organic solvent was removed in vacuo to yield (S)-2-Amino-5-cyclohexyl-pentanoic acid 2 (52 mg, quant.) as a white solid: 1H-NMR (400 MHz, CD3OD) δ=3.50 (dd, J=5.2, J=6.9, 1H), 1.88–1.64 (m, 7H), 1.47–1.37 (m, 2H), 1.31–1.11 (m, 6H), 0.94–0.86 (m, 2H). MS calcd. for C11H22NO2 (M+H+) 200.17. found 200.4. Step B: (S)-2-Amino-5-cyclohexyl-pentanoic acid 2 (24 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)-5-Cyclohexyl-2-(3-methyl-benzoylamino)-pentanoic acid 3 (19 mg, 50%) as a white solid: 1H-NMR (400 MHz, CD3OD) δ=7.67–7.62 (m, 2H), 7.37–7.31 (m, 2H), 4.56 (dd, J=5.0, J=9.4, 1H), 2.40 (s, 3H), 1.96–0.84 (m, 17H). MS calcd. for C19H28NO3 (M+H+) 318.21. found 318.4. Step C: (S)-5-Cyclohexyl-2-(3-methyl-benzoylamino)-pentanoic acid 3 (19 mg, 0.06 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-{4-Cyclohexyl-1-[2-(4-methoxy-phenylamino)-ethylcarbamoyl]-butyl}-3-methyl-benzamide 4 (15 mg, 0.03 mmol, 50%) as a white solid: 1H-NMR (400 MHz, CD3OD) δ=7.70–7.65 (m, 2H), 7.38–7.32 (m, 4H), 7.03–6.99 (m, 2H), 4.39 (dd, J=6.4, J=8.4, 1H), 3.80 (s, 3H), 3.67–3.61 (m, 1H), 3.54–3.41 (m, 3H), 2.38 (s, 3H), 1.88–1.80 (m, 2H), 1.72–1.66 (m, 5H), 1.64–1.36 (m, 2H), 1.29–1.07 (m, 6H), 0.92–0.83 (m, 2H). MS calcd. for C28H40N3O3 (M+H+) 466.31. found 466.5.
