Synthesis, characterisation and biological activity of cycloaurated organogold(III) complexes with imidate ligands

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The reactions of the cycloaurated gold(III) complexes (2-bp)AuCl 2 (2-bp = 2-benzylpyridyl) or (damp)AuCl 2 (damp = Me 2NCH 2C 6H 4) with an excess of sodium saccharinate (Nasacc), potassium phthalimidate (Kphth), or with isatin and trimethylamine in refluxing methanol results in the successful isolation of a series of new gold(III) imidate complexes. These were characterised by NMR and IR spectroscopies, and by X-ray structure determinations on (2-bp)Au(sacc) 2 and (2-bp)Au(phth) 2. In both structures, the planes of the saccharinate and the phthalimidate ligands are orientated almost perpendicular to the gold coordination plane. As expected from trans-influence considerations, the Au–N (imidate) bond lengths trans to the aryl carbon atoms are longer than the Au–N (imidate) bond lengths trans to the pyridyl groups. The complexes have also been characterised by electrospray ionisation MS; in the presence of halide ligands, one imidate ligand is readily displaced. Anti-tumour (P388 murine leukemia) and selected anti-microbial data for the new complexes are reported. Surprisingly, all three damp complexes had low anti-tumour activity, which is likely to be a consequence of the poor solubility of these complexes. The synthesis and characterisation of a related gold(III) bis(amidate) complex derived from sulfathiazole is also described.