1 H NMR ( 300 MHz , DMSO - d 6 ) δ : 10 . 28 ( br s , 1 H ) , 8 . 16 ( d , J = 8 . 2 Hz , 1 H ) , 8 . 10 ( br s , 1 H ) , 7 . 77 ( d , J = 8 . 0 Hz , 1 H ) , 7 . 64 - 7 . 58 ( m , 2 H ) , 7 . 21 - 7 . 15 ( m , 3 H ) , 6 . 94 ( d , J = 8 . 3 Hz , 2 H ) , 6 . 75 - 6 . 72 ( m , 1 H ) , 4 . 00 ( s , 3 H ) .