To a room temperature CH2Cl2 solution (400 mL) of 3-benzyloxy-4-chlorosulfonyl-benzoic acid methyl ester (11.43 g, 33.50 mmol) was added (S)-3-amino-succinamic acid tert-butyl ester (6.32 g, 33.50 mmol) and pyridine (10.80 mL). The reaction mixture was allowed to stir for 12 h at room temperature. The reaction was then diluted with ethyl acetate and washed with 5% citric acid and saturated NaHCO3. The organic phase was dried (MgSO4), and then the solvent was removed under vacuum. The resulting crude product was purified using silica gel flash chromatography (3% MeOH in CH2Cl2). 3-Benzyloxy-4-((S)-2-tert-butoxycarbonyl-1-carbamoyl-ethylsulfamoyl)-benzoic acid methyl ester was obtained in 45% yield (7.40 g) as an off white foam. MS m/z 491.2 (M−1).
