1 H NMR ( 500 MHz , DMSO - d 6 ) : δ ppm 12 . 05 ( s , 1 H ) , 10 . 55 ( s , 1 H ) , 8 . 01 - 7 . 94 ( m , 3 H ) , 7 . 79 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 59 ( dd J 1 = J 2 = 8 . 0 Hz , 1 H ) , 7 . 54 ( s , 1 H ) , 7 . 31 ( d , J = 8 . 5 Hz , 1 H ) , 7 . 23 ( s , 1 H ) , 7 . 07 ( s , 1 H ) , 4 . 12 ( s , 3 H ) . ( ESI ) : m / z 401 . 9 [ M + H ] +.