1 H NMR ( 400 MHz , DMSO - d 6 ) δ 9 . 90 ( s , 1 H ) , 8 . 03 ( d , J = 2 . 0 Hz , 1 H ) , 7 . 58 - 7 . 60 ( m , 2 H ) , 7 . 23 - 7 . 31 ( m , 3 H ) , 7 . 06 ( ddd , J = 2 . 0 , 4 . 8 , 8 . 4 Hz , 1 H ) , 6 . 98 ( m , 1 H ) , 6 . 52 ( dd , J = 7 . 2 , 7 . 2 Hz , 1 H ) .