A mixture of (R)-ethyl 3-amino-4-(3′-chlorobiphenyl-4-yl)butanoate hydrochloride (173 mg, 0.488 mmol), 2-(ethoxycarbonylamino)acetic acid (86 mg, 0.488 mmol), EDCl (140 mg, 0.732 mmol), DIPEA (0.128 ml, 0.732 mmol) and HOAt (100 mg, 0.732 mmol) in DMF (2.5 ml) is allowed to stir at room temperature for 1 hour. The reaction mixture is diluted with water, and then the precipitated solid is collected on a funnel, washed with H2O, and dried under reduced pressure to give crude. The obtained residue is purified by silica gel flash column chromatography (heptane/EtOAc=100:0 to 0:100) to give (R)-ethyl 4-(3′-chlorobiphenyl-4-yl)-3-(2-(ethoxycarbonylamino)acetamido)butanoate (161 mg); HPLC retention time=1.16 minutes (condition B); MS (m+1)=447.3; 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 1.25 (t, J=7.07 Hz, 3 H) 1.29 (t, J=7.07 Hz, 3 H) 2.50 (A of ABX, Jab=16.2 Hz, Jax=5.3 Hz, 1 H) 2.54 (B of ABX, Jab=16.2 Hz, Jbx=5.3 Hz, 1 H) 2.89 (A of ABX, Jab=13.6 Hz, Jax=7.8 Hz, 1 H) 2.99 (B of ABX, Jab=13.6 Hz, Jbx=6.6 Hz, 1 H) 3.80 (be d, J=5.8 Hz, 2 H) 4.12-4.23 (m, 4 H) 4.48-4.56 (m, 1 H) 5.15 (br s, 1 H) 6.64 (br d, J=8.8 Hz, 1 H) 7.25-7.27 (m, 2 H) 7.29-7.38 (m, 2 H) 7.43-7.46 (m, 1 H) 7.49-7.52 (m, 2 H) 7.55-7.56 (m, 1 H).
