Trifluoroacetic acid → (S)-3-((S)-3-(4-(3-Aminobenzyloxy)phenyl)-3-(isoxazol-3-yl)propanoyl)-4-benzyloxazolidin-2-one

To a cooled solution (0° C.) of carbamate 27.2 (430 mg, 0.719 mmol) in DCM (4 mL), was slowly added TFA (4 mL). The reaction mixture was allowed to slowly warm to room temperature over three hours. The mixture was then concentrated to dryness under reduced pressure and dissolved in DCM (100 mL). The resulting mixture was extracted with saturated sodium bicarbonate solution (1×30 mL). The aqueous layer was then extracted with DCM (1×50 mL). The organic layers were then combined and washed with brine (1×50 mL) and dried over magnesium sulfate. The filtrate was concentrated, and the residue was purified by medium pressure chromatography (silica gel, 20 to 60% EtOAc:DCM) to give 27.3 (204 mg). MS ESI (pos.) m/e 498.1 (M+H). 1H NMR (400 MHz, CDCl3) δ ppm 8.21 (1 H, d, J=1.6 Hz), 7.09-7.29 (8 H, m), 6.75-6.88 (4 H, m), 6.68 (1 H, dd, J=7.6, 2.2 Hz), 6.06 (1 H, d, J=1.6 Hz), 4.89 (2 H, s), 4.67 (1 H, dd, J=8.2, 6.7 Hz), 4.50-4.58 (1 H, m), 4.01-4.06 (2 H, m), 3.94 (1 H, dd, J=17.6, 8.6 Hz), 3.42-3.49 (1H, m), 3.13 (1 H, dd, J=13.5, 3.3 Hz), 2.68 (1 H, dd, J=13.5, 9.6 Hz).