1 H NMR ( 400 MHz , DMSO - d 6 ) δ 9 . 88 ( d , J = 1 . 2 Hz , 1 H ) , 8 . 04 ( t , J = 1 . 9 Hz , 1 H ) , 7 . 70 ( d , J = 1 . 7 Hz , 1 H ) , 7 . 66 - 7 . 58 ( m , 1 H ) , 7 . 50 ( dd , J = 1 . 9 , 0 . 9 Hz , 1 H ) , 7 . 36 ( dd , J = 8 . 5 , 1 . 7 Hz , 1 H ) , 7 . 00 ( dd , J = 2 . 3 , 1 . 0 Hz , 1 H ) , 6 . 33 ( dt , J = 3 . 1 , 1 . 7 Hz , 1 H ) , 6 . 15 ( s , 1 H ) , 6 . 12 - 5 . 99 ( m , 1 H ) , 4 . 14 ( d , J = 6 . 8 Hz , 2 H ) .