Triorganotin(IV) derivatives with semirigid heteroditopic hydroxo‐carboxylato ligands: Synthesis, characterization, and cytotoxic properties

Abstract

Three organic hydroxy‐carboxylic acids separated by a semirigid aromatic diaza scaffold and carrying alkyl groups of different steric hindrance (H′HL1, cyclopropyl; H′HL2, cyclohexyl; H′HL3, adamantyl) were employed as pro‐ligands. Their reaction with suitable triorganotin precursors leads to 10 complexes of compositions: [Me3Sn(HL1)]n·0.5nC6H5CH3 1, [Et3Sn(HL1)]n 2, [nBu3Sn(HL1)]n 3, [Ph3Sn(HL1)]n 4, [Me3Sn(HL2)]2·2CH2Cl2 5, [Et3Sn(HL2)]2 6, {[nBu3Sn(HL2)][nBu3Sn(HL2)(H2O)]} 7, [Ph3Sn(HL2)]n·nC2H5OH 8, [nBu3Sn(HL3)]n 9, and [Ph3Sn(HL3)]n 10. The solid‐state structures of 1–10 were deduced from single‐crystal X‐ray diffraction studies along with two of the pro‐ligands: H′HL1 and H′HL2. In the solid state, four different extended structure types were observed. In compounds 1–3 with aliphatic substituents at the tin atoms and a small substituent at the ligand backbone (cyclopropyl), 1D coordination polymers based on carboxylate bridging were observed, whereas compounds 4 and 8–10 with large substituents attached to the metal and the ligand (cyclohexyl and adamantyl) were 1D coordination polymers based on heteroditopic binding of the ligands. Albeit having essentially the same ligand conformation, the compounds having smaller substituents at the tin atoms (5, R = Me; 6, R = Et) comprise 24‐membered macrocyclic ring structures. In 7, water molecules are coordinated to half the tin atoms, giving dinuclear fragments {[HL2][nBu3Sn][HL2][nBu3Sn(H2O)]}, which are linked through OwH···Osal hydrogen bonds into 1D hydrogen‐bonded tapes. In solution, the tin atoms in 1–10 are coordinated to a single monoanionic [HL1–3]− ligand molecule utilizing anisobidentate coordination with the carboxylate group, as revealed from 119Sn nuclear magnetic resonance spectral results. The antiproliferative activity of the tri‐n‐butyl and triphenyltin compounds 3, 4, and 7–10 was evaluated against the cervical cancer cells (HeLa) and normal kidney cells (HEK) using the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay. Of these, the adamantyl‐substituted tin complexes 9 and 10 present increased activity with IC50 values of 0.51 ± 0.01 and 0.41 ± 0.03 (μM) and good selectivity. The cell death mechanism was identified as apoptosis based on dual staining with fluorescent dyes (Hoechst 33342/propidium iodide and acridine orange/ethidium bromide) and might be related to reactive oxygen species.