(S. Kato et al., J. Chem. Soc., Perkin Trans. 1997, 1, 3219-3225; J. Smrt et al., Experientia 1957, 15, 291). Crude (R)-methyl 3-hydroxy-2-(N-tritylamino)propanoate (45.20 g, 0.13 mol) was dissolved in CH2Cl2 (300 mL) and cooled to 0° C. under Ar. Methanesulfonyl chloride (10.64 mL, 0.14 mol) was added to the cooled solution, followed by the dropwise addition of Et3N (26.14 mL, 0.19 mol). The resulting solution was allowed to stir at 0° C. (30 min) and then successively washed with 10% aqueous citric acid (200 mL) and saturated aqueous brine (200 mL). After drying (Na2SO4) and evaporation of the solvent, the crude mesylate (53.30 g, 0.12 mol) was dissolved in DME (300 mL) and Et3N (33.73 mL, 0.24 mol) was added. The reaction mixture was stirred at 80° C. (48 h) and then evaporated in vacuo. The residue was dissolved in EtOAc (300 mL) and washed with 10% aqueous citric acid (200 mL) and saturated aqueous brine (200 mL). The organic layer was dried (Na2SO4) and evaporated in vacuo. The crude product was recrystallized (EtOH) to yield 30.81 g (74%) of desired product as a transparent crystal: mp 127-128° C. (Kato, S. et al., J. Chem. Soc., Perkin Trans. 1997, 1, 3219-3225; mp 129-131° C.); [α]20D +94.7° (c 1.5, CHCl3) (Smrt, J. et al., Experientia 1957, 15, 291; [α]20D +95 (c 1, CHCl3)); Rf=0.45 (1/5 EtOAc/hexanes); 1H NMR (CDCl3) δ 1.41 (dd, J=1.7, 6.4 Hz, NCHH′CH), 1.89 (dd, J=2.8, 6.4 Hz, CHH′CHN), 2.26 (dd, J=1.7, 2.8 Hz, NCHH′CH), 3.76 (s, OCH3), 7.20-7.31 (m, 9 PhH), 7.48-7.52 (m, 6 PhH); 13C NMR (CDCl3) δ 28.8 (NCH2CH), 31.8 (CH2CHN), 52.2 (OCH3), 74.5 (NCPh3), 127.1, 127.8, 129.4, 143.7 (3 C6H5), 172.0 (C(O)).
