1 H NMR ( 400 MHz , DMSO - d 6 ) : δ [ ppm ] = 3 . 69 - 3 . 77 ( m , 1 H ) , 3 . 82 - 3 . 88 ( m , 1 H ) , 3 . 94 ( s , 3 H ) , 4 . 88 ( dt , 1 H ) , 5 . 48 ( s , 1 H ) , 7 . 90 ( d , 2 H ) , 8 . 15 ( s , 1 H ) , 8 . 32 ( d , 2 H ) , 8 . 61 ( s , 1 H ) , 8 . 71 ( s , 1 H ) , 10 . 10 ( d , 1 H ) .