The 3-(4-amino-2-benzyloxy-benzenesulfonylamino)-N-methoxy-N-methyl-succinamic acid tert-butyl ester (5.56 g, 11.3 mmol) was dissolved in 100 mL methylene chloride, and triethylamine (2.8 mL) is added. One equivalent of acetyl chloride was added and stirred at room temperature. Additional portions of acetyl chloride were added approximately every 30 min until the starting material was consumed. (A total of 1.5 equivalents of acetyl chloride was used over about 2 hours.) The solvent was removed and replaced with ethyl acetate. The organic solution was washed twice with 5% cold HCl, then once with water, once with saturated potassium carbonate, then once with brine. The solution was dried over anhydrous magnesium sulfate, filtered and the solvent removed. The product was chromatographed with 30% chloroform/ethyl acetate, to yield 5.16 g (85%) of 3-(4-acetylamino-2-benzyloxy-benzenesulfonylamino)-N-methoxy-N-methyl-succinamic tert-butyl ester acid as a yellow foam. 1H NMR (CDCl3) 7.73 (1H, d, J=8.42 Hz), 7.6-7.5 (4H, m), 7.5-7.3 (3H, m), 6.9 (1H, d, J=8.6 Hz), 5.85 (1H, d, J=9.52), 5.3-5.1 (2H, m), 4.8-4.6 (1H, m), 3.56 (3H, s), 2.92 (3H, s), 2.7-2.38 (2H, m), 2.14 (3H, s), 1.40 (9H, s).
