1 H NMR ( 400 MHz , DMSO - d 6 ) : δ ppm 11 . 99 ( s , 1 H ) , 10 . 08 ( s , 1 H ) , 8 . 18 ( s , 1 H ) , 8 . 09 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 89 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 74 ( d , J = 8 . 8 Hz , 1 H ) , 7 . 35 ( d , J = 6 . 0 Hz , 2 H ) , 6 . 57 ( s , 1 H ) , 4 . 22 ( s , 3 H ) , 2 . 10 - 2 . 02 ( m , 1 H ) , 1 . 10 - 1 . 04 ( m , 2 H ) , 0 . 89 - 0 . 84 ( m , 2 H ) . ( ESI ) : m / z 427 . 1 [ M + H ] +.