General procedure B for alkylation of the sulphonamide nitrogen

B1: R_N = CH₃. A mixture of the corresponding sulphonamide (1 mmol) and crushed KOH (2 mmol) in CH₃CN (50 ml) was stirred for 30 min. Then, CH₃I (2 mmol) was added and stirred at room temperature for 24 h. The solvent was removed under reduced pressure. The residue was re-dissolved in EtOAc and washed with brine, dried (Na₂SO₄), and concentrated in vacuum. Crude reaction products were further purified to afford the corresponding methylated sulphonamides (2, 12, 14, 22, 24, and 33).

B2: R_N ≠ CH₃. To a solution of the sulphonamide derivative (1 mmol) in dry DMF (3 ml), K₂CO₃ (2 mmol) was added and the mixture was stirred for 1 h at room temperature. Then, the appropriate alkyl halide (2 mmol) was added, and the mixture was stirred at room temperature for 24 h. The solution was concentrated in a vacuum and redissolved in EtOAc. Then, it was washed with brine, dried over Na₂SO_4, and evaporated to dryness to give a crude reaction product which was further purified (3–7, 15–18, 25–28, and 34–37).