Three organotin(IV) Schiff-base carboxylates: Synthesis, structural characterization and in vitro cytotoxicity against cis-platin-resistent cancer cells

Abstract

Three new organotin(IV) complexes, namely trimethyltin(IV) [3‑methoxy-2-hydroxyphenyl-N-(3-carboxyphenyl) imine] monohydrate carboxylate, [Me3Sn(L)(H2O), 1], triphenyltin(IV) [3‑methoxy-2-hydroxyphenyl-N-(3-carboxyphenyl) imine] carboxylate, [Ph3Sn(L), 2], and di-n-butyltin(IV) [3‑methoxy-2-hydroxyphenyl-N-(3-carboxyphenyl) imine] carboxylate, ({[(n-Bu)2Sn(L)]2O}2, 3), [HL = 3‑methoxy-2-hydroxyphenyl-N-(3-carboxyphenyl) imine Schiff base ligand], have been synthesized by the reaction of organotin(IV) chlorides with Schiff base carboxylic acid ligand HL derived from o-vanillin and 3-aminobenzoic acid. All complexes have been characterized using spectroscopic (IR, 1H, 13C, 119Sn NMR, and ESI-MS) and single-crystal X-ray diffraction techniques. Structural analyses reveal that the ligand presents as monodentate in five-coordinate trimethyltin(IV) complex 1 and four-coordinate triphenyltin(IV) complex 2. But in di-n-butyltin(IV) complex 3, the ligands coordinate to tin(IV) atoms through bi- and monodentate two different forms. Also through intermolecular Sn···O weak interaction, complex 3 presents a weakly bridged dimmeric structure which will decompose to monomer in solution. The in vitro cytotoxicities of the title complexes determined against four cis-platin-resistent cancer cell lines (A549, Caco-2, HCT-116 and HT-29) reveal that the di-n-butyltin(IV) and triphenyltin(IV) complexes show higher cytotoxicities than trimethlytin(IV) derivative. The main anticancer mechanism should be due to the generation of intracellular reactive oxygen species (ROS).