1 H NMR ( CDCl 3 ) δ 8 . 55 ( 1 H , dd , J = 4 . 6 , 2 . 0 Hz ) , 7 . 55 ( 1 H , dd , J = 7 . 9 , 2 . 0 Hz ) , 7 . 19 ( 1 H , dd , J = 7 . 9 , 4 . 6 Hz ) , 6 . 31 ( 1 H , br s ) , 5 . 26 ( 1 H , d , J = 2 . 0 Hz ) , 3 . 93 ( 1 H , br ) , 3 . 77 ( 3 H , s ) , 2 . 92 - 2 . 73 ( 2 H , m ) , 2 . 30 ( 1 H , ddd , J = 13 . 2 , 8 . 6 , 4 . 3 Hz ) , 2 . 10 ( 1 H , ddd , J = 13 . 2 , 7 . 9 , 4 . 6 Hz ) .