1 H NMR ( CDCl 3 ) δ 8 . 42 ( 1 H , dd , J = 4 . 6 , 1 . 3 Hz ) , 7 . 54 ( 1 H , br d , J = 7 . 9 Hz ) , 7 . 15 ( 1 H , dd , J = 7 . 9 , 4 . 6 Hz ) , 5 . 86 ( 1 H , s ) , 3 . 86 ( 1 H , t , J = 5 . 3 Hz ) , 3 . 70 ( 3 H , s ) , 2 . 80 ( 1 H , m ) , 2 . 56 ( 1 H , m ) , 2 . 32 ( 1 H , m ) , 2 . 13 ( 1 H , m ) , 1 . 56 ( 9 H , s ) .