1 H NMR ( 500 MHz , DMSO - d 6 ) : δ ppm 12 . 18 ( s , 1 H ) , 10 . 07 ( s , 1 H ) , 8 . 97 ( s , J = 2 . 8 Hz ) , 1 H ) , 8 . 36 - 8 . 34 ( m , 1 H ) , 8 . 19 - 8 . 17 ( m , 2 H ) , 7 . 93 ( d , J = 8 . 0 Hz , 1 H ) , 7 . 64 ( dd , J 1 = 5 . 0 Hz , J 2 = 8 . 0 Hz , 1 H ) , 6 . 93 ( s , 1 H ) , 4 . 23 ( s , 3 H ) . ( ESI ) : m / z 388 . 1 [ M + H ] +.