1 H NMR ( 200 MHz , DMSO - d 6 ) δ 9 . 47 ( s , 1 H ) , 8 . 70 ( s , 1 H ) , 8 . 58 ( s , 1 H ) , 7 . 58 ( d , 2 H , J = 8 . 6 Hz ) , 7 . 42 ( d , 2 H , J = 8 . 6 Hz ) , 7 . 20 ( br s , 1 H ) , 6 . 79 ( m , 2 H ) , 5 . 97 ( s , 2 H ) , 5 . 71 ( s , 2 H ) .