New Coordination Modes of L‐Ascorbic Acid and Dehydro‐L‐ascorbic Acid as Dianionic Chelating Ligand for Platinum

Abstract

Abstract A variety of coordination modes of L ‐ascorbic acid as an anionic bidentate ligand has been exploited to prepare platinum(II) complexes 1 – 7 that contain phosphanes or R , R ‐dach (1 R ,2 R ‐diaminocyclohexane) as neutral ligands in which O2, O3, O5, O6 and C2 act as anionic donating functionalities. An alternative synthetic route to known O2,O3 complexes is proposed, and their solubility in water has been enhanced by introducing PTA (1,3,5‐triaza‐7‐phosphaadamantane) as a neutral ligand. A new coordination mode of ascorbic acid (O2 and O3 protected) as an O5,O6‐diolate chelating ligand has been characterised in solution by NMR spectroscopy and in the solid state by X‐ray crystallography. The first example of a platinum complex that contains dehydroascorbic acid, 7 , has also been prepared and its X‐ray crystal structure has been determined. The antiproliferative activity in vitro of complexes 1 – 7 has been tested, and the best values were obtained for the DHA complex 7 , which was found to be more active than cisplatin on both a cisplatin‐sensitive and a cisplatin‐resistant cell line.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)