Synthesis, Crystal Structure and Biological Characterization of a Novel Palladium(<scp>II</scp>) Complex with a Coumarin‐Derived Ligand

Abstract

Abstract Methyl 2‐methyl‐4‐oxo‐4 H ‐chromene‐3‐carboxylate ( 1 ) was treated with 25% aqueous ammonia to give 3‐(1‐aminoethylidene)‐2 H ‐chromene‐2,4(3 H )‐dione ( 2 ). Compound 2 was used as a ligand for the formation of a palladium( II ) complex. The structures of the ligand and its palladium complex 3 were determined by IR and 1 H NMR spectroscopy, FAB mass spectrometry and elemental analysis. The single‐crystal X‐ray structure of 3 was also solved. Ligand 2 in 20% dioxane solution shows two protonation constants — log β 11 = 4.28 ± 0.01 and log β 12 = 7.66 ± 0.03. In complex 3 two ligand molecules chelate to the Pd ion through their N and O donors, giving a four‐coordinate Pd II center with a cis ‐N 2 O 2 donor set. The coordination geometry at Pd II is square‐planar with typical values for the distances from the Pd atom to the coordinated atoms. The cytotoxicity of compound 3 was determined on three cancer cell lines. IC 50 values of 9.7, 7.8 and 7.8 n M were found for A546, HeLa and K562 cells, respectively, which is notably lower than carboplatin, which shows corresponding IC 50 values of 105.98, 73.49 and 60.92 μ M . Double‐stranded DNA treated with 3 shows a significant increase in the Δϵ value in the CD spectra, as well as a lower electrophoretic mobility than parent DNA. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)