1 H NMR ( 400 MHz , CDCl 3 ) δ 8 . 14 ( d , J = 8 . 4 Hz , 1 H ) , 7 . 71 ( d , J = 8 . 4 Hz , 1 H ) , 4 . 31 ( tt , J = 9 . 0 , 6 . 8 Hz , 1 H ) , 2 . 21 - 2 . 10 ( m , 2 H ) , 2 . 10 - 1 . 99 ( m , 2 H ) , 1 . 90 - 1 . 79 ( m , 2 H ) , 1 . 76 - 1 . 63 ( m , 2 H ) .