1 H NMR ( 300 MHz , DMSO - d 6 ) δ : 9 . 40 ( br s , 1 H ) , 8 . 20 - 8 . 14 ( m , 2 H ) , 7 . 75 - 7 . 59 ( m , 2 H ) , 6 . 83 ( br s , 1 H ) , 4 . 72 ( m , 1 H ) , 4 . 01 ( s , 3 H ) , 1 . 18 ( s , 9 H ) , 1 . 13 ( d , J = 6 . 8 Hz , 6 H ) .