1 H NMR ( CDCl 3 ) δ 8 . 74 ( 1 H , d , J = 4 . 6 Hz ) , 7 . 87 ( 1 H , d , J = 7 . 9 Hz ) , 7 . 39 ( 1 H , m ) , 5 . 61 ( 1 H , br d , J = 49 . 4 Hz ) , 3 . 80 ( 3 H , s ) , 2 . 57 - 2 . 40 ( 4 H , m ) .