Sodium hydride (20 mg) was added to a solution comprising 73 mg of compound 10a in 2 ml of anhydrous DMF at 0° C. The solution was stirred for 25 minutes and 126 mg of chlorosulfonamide was added in one portion. The solution was then stirred at room temperature for 2 hours. Ice and saturated sodium bicarbonate solution was added to the reaction mixture. The precipitate formed was filtered and washed with water. The residue was purified by chromatography on silica gel (CHCl3:methanol, 50:1), yielding compound 11a (85 mg, 96%). FAB-MS m/z 433 (M+H)+; 1H NMR (270 MHz, DMSO-d6) δ 0.88 (t, 3H, J=7.5 Hz, CH2CH3), 0.91 (s, 3H, CH3), 3.08 (dt, 2H, J=5.6, 6.6 Hz, NHCH2), 6.34 (s, 1H, 16-CH), 6.97 (s, 1H, ArH), 7.01 (dd, 1H, J=2.6, 8.6 Hz, ArH), 7.33 (d, 1H, J=8.6 Hz, ArH), 7.71 (t, 1H, J=5.6 Hz, NHCH2), 7.88 (s, 2H, NH2).
