1 H NMR ( 400 MHz , CDCl 3 ) δ 8 . 09 ( 1 H , d , J = 9 . 3 Hz ) , 7 . 47 - 7 . 41 ( 2 H , m ) , 7 . 37 - 7 . 32 ( 3 H , m ) , 6 . 58 ( 1 H , d , J = 9 . 3 Hz ) , 4 . 87 ( 2 H , s ) , 3 . 20 ( 6 H , s ) ;