1 H NMR ( 300 MHz , DMSO - d 6 ) δ 9 . 48 ( s , 1 H ) , 8 . 83 ( s , 1 H ) , 8 . 80 ( s , 1 H ) , 7 . 58 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 48 ( d , 2 H , J = 8 . 9 Hz ) , 7 . 43 ( d , 2 H , J = 8 . 7 Hz ) , 7 . 32 ( d , 2 H , J = 8 . 9 Hz ) , 5 . 72 ( s , 2 H ) .