1 H NMR ( 500 MHz , DMSO - d 6 ) : δ ppm 10 . 13 ( s , 1 H ) , 8 . 19 ( s , 1 H ) , 8 . 11 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 96 - 7 . 94 ( m , 2 H ) , 7 . 84 - 7 . 82 ( m , 1 H ) , 7 . 79 - 7 . 77 ( m , 1 H ) , 7 . 67 ( d , J = 7 . 5 Hz , 1 H ) , 6 . 55 ( s , 1 H ) , 4 . 23 ( s , 3 H ) , 3 . 49 ( s , 3 H ) . ( ESI ) : m / z 401 . 1 [ M + H ] +.