1 H NMR ( 400 MHz , chloroform - d 1 ) δ 7 . 56 ( m , 2 H ) , 7 . 13 ( d , J = 10 . 4 Hz , 1 H ) , 4 . 96 ( br s , 1 H ) , 4 . 80 - 4 . 74 ( m , 1 H ) , 4 . 01 ( t , J = 9 . 2 Hz , 1 H ) , 3 . 85 ( t , J = 6 . 4 Hz , 1 H ) , 3 . 53 - 4 . 09 ( t , J = 6 . 0 Hz , 2 H ) , 1 . 40 ( s , 9 H )