1 H NMR ( 400 MHz , DMSO - d 6 ) : δ [ ppm ] = 7 . 57 - 7 . 62 ( m , 2 H ) , 7 . 92 ( t , 1 H ) , 8 . 12 - 8 . 17 ( m , 2 H ) , 8 . 47 ( s , 1 H ) , 8 . 51 ( s , 1 H ) , 8 . 99 ( s , 1 H ) , 13 . 86 ( br s , 1 H ) .