1 H NMR ( 500 MHz , DMSO - d 6 ) : δ ppm 11 . 89 ( s , 1 H ) , 10 . 60 ( s , 1 H ) , 8 . 06 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 96 - 7 . 94 ( m , 1 H ) , 7 . 81 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 55 - 7 . 51 ( m , 4 H ) , 7 . 25 ( s , 1 H ) , 6 . 83 ( d , J = 2 . 0 Hz , 1 H ) , 4 . 12 ( s , 3 H ) . ( ESI ) : m / z 401 . 9 [ M + H ] +.