1 H NMR ( 400 MHz , CDCl 3 ) δ 9 . 38 ( s , 1 H ) , 9 . 30 ( br d , J = 9 . 2 Hz , 1 H ) , 8 . 18 ( d , J = 2 . 2 Hz , 1 H ) , 8 . 01 ( d , J = 8 . 8 Hz , 1 H ) , 7 . 75 ( dd , J = 9 . 2 , 2 . 2 Hz , 1 H ) , 4 . 83 - 4 . 71 ( m , 1 H ) , 3 . 27 ( ddd , J = 10 . 1 , 6 . 2 , 0 . 9 Hz , 1 H ) , 3 . 16 - 3 . 07 ( m , 2 H ) , 2 . 81 ( ddd , J = 9 . 9 , 5 . 7 , 2 . 0 Hz , 1 H ) , 2 . 46 ( s , 3 H ) .