To a solution of 15.6 g (49 mmol) (2S)-3-(4-hydroxyphenyl)-2-[(phenylmethoxy)carbonylamino]propanoic acid in 120 mL methanol was added 9.4 g (49 mmol) of p-toluenesulfonic acid monohydrate. The solution was heated to 70 ° C. for 2 h. After solution was cooled to room temperature, the methanol was removed under reduced pressure. The solid obtained was redissolved in 120 mL methylene chloride. The organic solution was then washed with dilute NaHCO3 solution twice and brine. The organic layer was dried with anhydrous MgSO4 and filtered. The solvent was removed under reduced pressure. The crude mixture was chromatographed on a silica gel column using 40% ethyl acetate in hexanes as the eluent to yield 15.6 g (96%) of white solid as product: 1H NMR (300 MHz, CDCl3) δ7.38-7.30 (m, 5H), 6.93 (d, J=8.41 Hz, 2H), 6.81 (d, J=8.41 Hz, 2H), 5.39 (br s, 1H), 5.24 (d, J=9.29 Hz, 1H), 5.11 (d, J=12.32 Hz, 1H), 5.06 (d, J=12.29 Hz, 1H), 4.61 (m, 1H), 3.71 (s, 3H), 3.06 (dd, J=5.88, 14.06 Hz, 1H), 2.98 (dd, J=5.88, 14.06 Hz, 1H)
