1 H NMR ( 300 MHz , DMSO - d 6 ) δ : 9 . 96 ( br s , 1 H ) , 8 . 25 ( d , J = 8 . 0 Hz , 1 H ) , 7 . 61 - 7 . 49 ( m , 7 H ) , 7 . 47 - 7 . 36 ( m , 1 H ) , 6 . 90 ( s , 1 H ) , 4 . 09 ( d , J = 6 . 6 Hz , 2 H ) , 2 . 15 - 2 . 11 ( m , 1 H ) , 1 . 01 ( d , J = 6 . 6 Hz , 6 H ) .