1H NMR (400 MHz, CDCl3) δ 8.97 (d, J = 18.8 Hz, 2H), 8.51 (d, J = 8.2 Hz, 1H), 8.38 (dd, J = 13.2, 7.8 Hz, 2H), 8.25 (d, J = 8.2 Hz, 1H), 7.78 (t, J = 8.0 Hz, 1H), 7.69 (t, J = 8.0 Hz, 1H), 7.49 (s, 1H), 2.57 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 178.7, 151.0, 150.4, 148.6, 148.2, 137.8, 134.9, 131.6, 130.6, 130.0, 130.0, 127.3, 124.4, 123.8, 123.5, 121.4, 121.1, 17.8. HRMS (EI): calcd for C18H12N2O6S: 384.0416; found, 384.0421.