To a stirred solution of benzoic acid 3-benzenesulfonylamino-4-benzyloxy-phenyl ester(which was obtained in Example 17) (2.88 g, 7.27 mmol) in DMF (20 mL) was added 60% sodium hydride (0.32 g, 8 mmol). After hydrogen evolution had subsided the stirred mixture was heated at 70° C. for 15 minute, and then it was cooled down to room temperature and a solution of benzyl chloride (1.01 g, 8 mmol) in 5 mL of DMF was added dropwise. The mixture was then heated at 85–90° C. for 2 hours, then it was cooled down to room temperature, poured into ice-water. The aqueous layer was extracted with ethyl acetate and the organic layer was dried and concentrated. The product was purified by flash silica gel chromatography eluting with ethyl acetate and hexanes to give the title compound as a white solid (2.40 g, 70%); 1H NMR (300 MHz, CDCl3) δ 4.74(s, 2 H), 4.83(s, 2 H), 8.83(d, J=8.9 Hz, 1 H), 8.10–8.50(m, 2 H); HRMS Calcd. for C33H28NO5S(MH+): 550.1688. Found: 550.1680.
