1 H - NMR ( 400 MHz , DMSO - d 6 ) δ : 7 . 92 ( 2 H , d , J = 8 . 8 Hz ) , 7 . 72 ( 2 H , d , J = 8 . 4 Hz ) , 7 . 45 - 7 . 30 ( 10 H , m ) , 6 . 99 ( 2 H , d , J = 9 . 2 Hz ) , 6 . 88 ( 2 H , d , J = 9 . 2 Hz ) , 5 . 17 ( 2 H , s ) , 5 . 08 ( 2 H , s ) .