1 H NMR ( DMSO - d 6 , 400 MHz ) δ 8 . 48 ( d , J = 9 . 0 Hz , 1 H ) , 6 . 75 ( d , J = 9 . 0 Hz , 1 H ) , 4 . 21 - 4 . 11 ( m , 1 H ) , 4 . 02 ( s , 3 H ) , 3 . 91 - 3 . 86 ( m , 2 H ) , 3 . 53 - 3 . 47 ( m , 2 H ) , 2 . 05 - 2 . 02 ( m , 2 H ) , 1 . 70 - 1 . 65 ( m , 2 H ) ;