. . . "All these groups can be substituted, examples of suitable substituents being the following: --COOH, --OH, --SH, C1 -C4 alkoxy (such as methoxy, ethoxy, propoxy, butoxy, isobutoxy), --NO2, --NH2, --NH(C1 -C4 alkyl), --NH--CO--NH2, --N(C1 -C4 alkyl)2, phenyl (unsubstituted or substituted by, for example, --OH or halogen, such as Cl, Br or in particular I), --S(C1 -C4 alkyl), 5- or 6-membered heteroc" .