To a solution of benzoic acid (0.57 g, 4.8 mmol) in anhydrous dichloromethane was added triethylamine (1.7 mL, 12 mmol) and 2,4,6-trichlorobenzoyl chloride (0.9 mL, 5.76 mmol). The mixture was stirred for 30 min and a solution of (1R,2R)-2-hydroxy-1-methylpropyl (2S)-2-[(tert-butoxy)carbonylamino]-3-[3,4-bis(phenylmethoxy)phenyl]propanoate (2.4 g, 4.4 mmol) in dichloromethane was slowly added to the reaction mixture, followed by the addition of a catalytic amount of 4-(dimethylamino)pyridine. The mixture was stirred at room temperature for 16 h, washed with 10% citric acid, dried over Na2SO4, and concentrated. Chromatography (silica gel, 20% ethyl acetate in hexane) of the residue afforded 2.6 g (90% yield) of (1R,2R)-1-methyl-2-phenylcarbonyloxypropyl (2S)-2-[(tert-butoxy)carbonylamino]-3-[3,4-bis(phenylmethoxy)phenyl]propanoate. 1H NMR (400 MHz, CDCl3): δ 1.26 (d, J=6.4 Hz, 6H), 1.39 (s, 9H), 2.78 (m, 1H), 2.96 (m, 1H), 4.51 (m, 1H), 4.89 (d, 1H), 5.10 (s, 4H), 5.15 (m, 1H), 6.57 (d, J=8 Hz, 1H), 6.71 (s, 1H), 6.77 (d, J=8 Hz, 1H), 7.25-7.43 (m, 12H), 7.52 (t, J=7.6 Hz, 1H), 7.99 (d, J=7.6 Hz, 2H).
