1 H NMR ( 500 MHz , DMSO - d 6 ) : δ ppm 12 . 08 ( s , 1 H ) , 10 . 12 ( s , 1 H ) , 8 . 18 ( s , 1 H ) , 8 . 12 ( d , J = 8 . 0 Hz , 1 H ) , 8 . 00 - 7 . 97 ( m , 1 H ) , 7 . 91 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 62 - 7 . 60 ( m , 1 H ) , 7 . 55 - 7 . 51 ( m , 1 H ) , 6 . 65 ( s , 1 H ) , 4 . 22 ( s , 3 H ) . ( ESI ) : m / z 405 . 1 [ M + H ] +.