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

Abstract

Abstract Reactions of potassium bis(oxalato)palladate dihydrate, K 2 [Pd(ox) 2 ]·2H 2 O, with two molar equivalents of N6-(benzyl)-9-isopropyladenine-based organic molecules (L 1–7 ), i.e. 2-chloro-N6-(2-methoxybenzyl)-9-isopropyladenine (L 1 ), 2-chloro-N6-(3-methoxybenzyl)-9-isopropyladenine (L 2 ), 2-chloro-N6-(3,5-dimethoxybenzyl)-9-isopropyladenine (L 3 ), 2-(1-ethyl-2-hydroxyethylamino)-N6-(benzyl)-9-isopropyladenine (L 4 ), 2-(1-ethyl-2-hydroxyethylamino)-N6-(2-methoxybenzyl)-9-isopropyladenine (L 5 ), 2-(1-ethyl-2-hydroxyethylamino)-N6-(3-methoxybenzyl)-9-isopropyladenine (L 6 ) and 2-(1-ethyl-2-hydroxyethylamino)-N6-(4-methoxybenzyl)-9-isopropyladenine (L 7 ), provided a series of seven palladium(II) oxalato (ox) complexes of the general formula [Pd(ox)(L 1–7 ) 2 ]· n H 2 O ( 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, 1 H, 13 C and 15 N{ 1 H} NMR spectroscopy, ESI+ mass spectrometry, molar conductivity and TG/DTA thermal analysis. The geometry of [Pd(ox)(L 2 ) 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 PdN 2 O 2 donor set, which involve highly potent purine-based cyclin-dependent kinase (CDK) inhibitors (L 4–7 ) 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 (IC 50 = 34.9 μM) and 7 (IC 50 = 39.2 μM).