1 H NMR ( 400 MHz , DMSO - d 6 ) δ 10 . 68 ( s , 1 H ) , 8 . 61 ( s , 1 H ) , 7 . 68 ( s , 1 H ) , 7 . 55 ( d , J = 8 . 4 Hz , 1 H ) , 7 . 33 ( dd , J = 2 . 0 , 8 . 8 Hz , 1 H ) , 7 . 00 - 7 . 06 ( m , 1 H ) , 6 . 92 ( s , 1 H ) , 6 . 39 - 6 . 57 ( m , 3 H ) , 4 . 53 ( s , 2 H ) , 3 . 34 ( s , 3 H ) .