1 H NMR ( 300 MHz , DMSO - d 6 ) δ 10 . 19 ( s , 1 H ) , 9 . 55 ( s , 1 H ) , 7 . 62 ( s , 4 H ) , 7 . 36 ( d , 2 H , J = 9 . 0 Hz ) , 7 . 02 ( d , 2 H , J = 9 . 0 Hz ) , 5 . 75 ( s , 2 H ) , 4 . 72 ( s , 2 H ) .