Palladium(II) oxalato complexes involving N6-(benzyl)-9-isopropyladenine-based N-donor carrier ligands: Synthesis, general properties, 1H, 13C and 15N{1H} NMR characterization and in vitro cytotoxicity

Reactions of potassium bis(oxalato)palladate dihydrate, K2[Pd(ox)2]·2H2O, with two molar equivalents of N6-(benzyl)-9-isopropyladenine-based organic molecules (L1–7), i.e. 2-chloro-N6-(2-methoxybenzyl)-9-isopropyladenine (L1), 2-chloro-N6-(3-methoxybenzyl)-9-isopropyladenine (L2), 2-chloro-N6-(3,5-dimethoxybenzyl)-9-isopropyladenine (L3), 2-(1-ethyl-2-hydroxyethylamino)-N6-(benzyl)-9-isopropyladenine (L4), 2-(1-ethyl-2-hydroxyethylamino)-N6-(2-methoxybenzyl)-9-isopropyladenine (L5), 2-(1-ethyl-2-hydroxyethylamino)-N6-(3-methoxybenzyl)-9-isopropyladenine (L6) and 2-(1-ethyl-2-hydroxyethylamino)-N6-(4-methoxybenzyl)-9-isopropyladenine (L7), provided a series of seven palladium(II) oxalato (ox) complexes of the general formula [Pd(ox)(L1–7)2]·nH2O (1–7; n = 0 for 4, 5 and 7, ¾ for 1 and 2, 1 for 6, and 3 for 3). The compounds were characterized by elemental analysis, IR, Raman, 1H, 13C and 15N{1H} NMR spectroscopy, ESI+ mass spectrometry, molar conductivity and TG/DTA thermal analysis. The geometry of [Pd(ox)(L2)2] (2) was optimized on the B3LYP/6-311G∗/LANL2DZ level of theory. The complexes 4–7 represent the first palladium(II) oxalato complexes with a PdN2O2 donor set, which involve highly potent purine-based cyclin-dependent kinase (CDK) inhibitors (L4–7) as carrier N-donor ligands. The selected complexes 1, 3–5 and 7 were tested by an MTT assay for their in vitro cytotoxic activity against human osteosarcoma (HOS) cancer cell line. The highest activity was found for the complexes 5 (IC50 = 34.9 μM) and 7 (IC50 = 39.2 μM).

A series of palladium(II) oxalato complexes of the composition [Pd(ox)(L1–7)2]·nH2O (1–7), involving N6-(benzyl-substituted)-9-isopropyladenine derivatives as the N-donor carrier ligands, were prepared by the reactions of K2[Pd(ox)2]·2H2O with the appropriate adenine derivative. The complexes were fully characterized by various physical methods and tested for their in vitro cytotoxicity against HOS human cancer cell line.Figure optionsDownload as PowerPoint slide