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).