1 H NMR ( 400 MHz , CDCl 3 ) δ 10 . 2 - 9 . 4 ( v br s , 1 H ) , 9 . 44 ( s , 1 H ) , 8 . 33 ( d , J = 8 . 8 Hz , 1 H ) , 7 . 86 ( dd , J = 8 . 6 , 1 . 7 Hz , 1 H ) , 7 . 43 ( s , 1 H ) , 6 . 41 - 6 . 09 ( m , 2 H ) , 5 . 96 ( d , J = 15 . 6 Hz , 1 H ) , 3 . 75 - 3 . 57 ( br m , 1 H ) , 3 . 70 ( dd , J = 11 . 7 , 11 . 7 Hz , 1 H ) , 3 . 17 - 3 . 03 ( m , 1 H ) , 3 . 15 ( dd , J = 11 . 2 , 11 . 2 Hz , 1 H ) , 2 . 65 ( br s , 3 H ) , 2 . 32 ( s , 3 H ) .