1 H NMR ( 300 MHz , DMSO - d 6 ) δ : 8 . 03 ( d , J = 7 . 9 Hz , 1 H ) , 7 . 81 - 7 . 75 ( m , 5 H ) , 7 . 59 ( t , J = 7 . 1 Hz , 1 H ) , 7 . 43 ( t , J = 7 . 0 Hz , 1 H ) , 6 . 52 ( d , J = 7 . 3 Hz , 1 H ) , 3 . 89 - 3 . 87 ( m , 1 H ) , 1 . 34 - 1 . 31 ( d , J = 6 . 8 Hz , 6 H ) .