1 H NMR ( 300 MHz , DMSO - d 6 ) δ 10 . 63 ( s , 1 H ) , 9 . 60 ( s , 1 H ) , 8 . 02 ( d , 2 H , J = 1 . 9 Hz ) , 7 . 87 ( t , 1 H , J = 1 . 8 Hz ) , 7 . 77 ( d , 2 H , J = 8 . 7 Hz ) . 7 . 65 ( d , 2 H , J = 8 . 7 Hz ) , 5 . 81 ( s , 2 H ) .