The crude N-aryl-benzenesulfonamide building block XIII, e.g. 4-ethoxy-N-(4-methylphenyl)benzenesulfonamide (204 mg, 0.70 mmol, preparation described in example 1, step a)), was dissolved in DMF (5 mL). Methyl-2-bromopropionate (0.117 mL, 1.05 mmol) and potassium carbonate (193 mg, 1.40 mmol) were added. The mixture was heated overnight at 60° C. Solvents were evaporated. The crude residue was suspended in ethyl acetate (10 mL) and was washed with 1N HCl solution (7 mL) and with brine (7 mL). Organic phase was dried over MgSO4, fltrated and evaporated. The desired product, e.g. methyl 2-{[(4-ethoxyphenyl)sulfonyl]-4-methylanilino}propanoate (276 mg, quantitative crude yield) was isolated as a light yellow oil, in 94.3% purity by HPLC (MaxPlot detection between 230 and 400 nm).
