Next, to a solution of (2R,4S)-5-biphenyl-4-yl-4-(3,5-difluoro-4-methoxy-benzoylamino)-2-methyl-pentanoic acid ethyl ester (125 mg, 0.260 mmol) in DCM (2.6 mL) is slowly added BBr3 (2.60 mL, 2.60 mmol) under nitrogen. The reaction is stirred for 18 hours at rt. The reaction is quenched with MeOH, diluted with EtOAc, washed with H2O and brine, dried over MgSO4, and concentrated under reduced pressure. The obtained material is purified by preparative silica gel thin-layer chromatography (7% MeOH in DCM) to give 100 mg (2R,4S)-5-biphenyl-4-yl-4-(3,5-difluoro-4-hydroxy-benzoylamino)-2-methyl-pentanoic acid ethyl ester. Next, to a solution of (2R,4S)-5-biphenyl-4-yl-4-(3,5-difluoro-4-hydroxy-benzoylamino)-2-methyl-pentanoic acid ethyl ester (30 mg, 0.064 mmol) in MeOH (2 mL) at room temperature is added aqueous 1M NaOH (4 mL, 4.0 mmol). After stirring for 1 hour the reaction is quenched with aqueous 1M HCl (4 mL, 4.0 mmol). The mixture is concentrated under reduced pressure and filtered to remove NaCl salt. The obtained residue is purified by preparative silica gel thin-layer chromatography (7% MeOH in DCM) to give 17.1 mg of (2R,4S)-5-biphenyl-4-yl-4-(3,5-difluoro-4-hydroxy-benzoylamino)-2-methyl-pentanoic acid. HPLC Retention time 1.56 minutes (condition B); MS 440 (M+1); 1H NMR (400 MHz, ACETONITRILE-d3) δ ppm 1.19 (d, J=7.07 Hz, 3 H) 1.55 (ddd, J=14.27, 10.74, 3.79 Hz, 1 H) 1.90-1.96 (m, 1 H) 2.54-2.71 (m, 1 H) 2.91 (dd, J=6.69, 3.16 Hz, 2 H) 4.25-4.43 (m, 1 H) 6.49 (d, J=9.60 Hz, 2 H) 6.93 (d, J=8.84 Hz, 1 H) 7.33-7.42 (m, 3 H) 7.49 (t, J=7.71 Hz, 2 H) 7.61 (d, J=8.34 Hz, 2 H) 7.67 (dd, J=8.34, 1.26 Hz, 2 H).
