1 H NMR ( 400 MHz , DMSO - d 6 ) : δ [ ppm ] = 3 . 46 - 3 . 54 ( m , 1 H ) , 3 . 74 - 3 . 82 ( m , 1 H ) , 3 . 94 ( s , 3 H ) , 4 . 19 - 4 . 30 ( m , 1 H ) , 6 . 71 ( s , 1 H ) , 7 . 90 ( d , 2 H ) , 8 . 14 ( s , 1 H ) , 8 . 30 ( d , 2 H ) , 8 . 56 ( s , 1 H ) , 8 . 67 ( s , 1 H ) , 9 . 72 ( t , 1 H ) .