Post-Synthetic Modification Research of Salan Titanium bis-Chelates via Sonogashira Reaction

Synthesis, in vitro antitumor evaluation and structure activity relationship of heptacoordinated amino-bis(Phenolato) Ti(IV) complexes stabilized by 2,6-dipicolinic acid

Eighteen novel Ti(IV) complexes stabilized by different chelating amino-bis(phenolato) (ONNO, ONON, ONOO) ligands and 2,6-dipicolinic acid as a second chelator were synthesized with isolated yields ranging from 79 to 93%. Complexes were characterized by 1H and 13C-NMR spectroscopy, as well as by HRMS and X-Ray diffraction analysis. The good to excellent aqueous stability of these Ti(IV) complexes can be modulated by the substitutions on the 2-position of the phenolato ligands. Most of the synthesized Ti(IV) complexes demonstrated potent inhibitory activity against Hela S3 and Hep G2 tumor cells. Among them, the naphthalenyl based Salan type 2j, 2-picolylamine based [ONON] type 2n and N-(2-hydroxyethyl) based [ONOO] type 2p demonstrated up to 40 folds enhanced cytotoxicity compared to cisplatin together with a significantly reduced activity against healthy AML12 cells. The three Ti(IV) complexes exhibited fast cellular uptake by Hela S3 cells and induced almost exclusively apoptosis. 2j could trigger higher level of ROS generation than 2p and 2n.

Synthesis and X-ray structure analysis of cytotoxic heptacoordinated Salan hafnium(IV) complexes stabilized with 2,6-dipicolinic acid

Four novel Salan Hf^(IV) complexes stabilized by 2,6-dipicolinic acid (Dipic) were synthesized and characterized by ¹H, ¹³C NMR and X-ray diffraction spectroscopy. These Hf^(IV)bis-chelates could be obtained in good to excellent yields (88%-91%) and demonstrated rather good stability in aqueous media and on silica gel. [L₂Hf^(IV)Dipic^4-H,Cl] containing steric bulk L₂ were stable in about 10% H₂O (H₂O/THF (v/v)), however, [L₁Hf^(IV)Dipic^4-H,Cl] with non-steric L₁ could slowly dissociate and release nontoxic L₁. [L_1-2Hf^(IV)Dipic^4-Cl] showed excellent anti-tumoral activity in the range of cisplatin (Hela S3: IC₅₀ = 3.5 ± 0.4 μM, Hep G2: IC₅₀ = 11.2 ± 2.1 μM). In addition, the cellular uptake and apoptosis investigation of [L₁Hf^(IV)Dipic^4-Cl] suggested a fast cellular uptake process against Hela S3 cells with an almost exclusive induced apoptosis cell death path.

Facile synthesis of [ONON] type titanium(IV)bis-chelated complexes in alcoholic solvents and evaluation of anti-tumor activity

Novel anti-tumoral diamino-bis-(phenolato) [ONON] type titanium^(IV) complexes stabilized by 2,6-dipicolinic acid were synthesis via an efficient protocol using n-propanol as solvent and H₂O for isolation. In total 20 [ONON] type and 2 Salan Ti^(IV)bis-chelated complexes were synthesized with yields ranging from 68% to 96%. All reactions could reach to completion in 1.5 min at 80 °C either using Ti(OⁱPr)₄ or TiCl₄ as starting materials. Most [ONON] type Ti^(IV) complexes exhibit selectively enhanced inhibition activity against Hep G2 cells in comparison with Salan Ti^(IV) complexes. Among which, the inhibitory activity of 2 t (IC₅₀: 0.15 ± 0.1 μM) against Hep G2 cells is about 80 times enhanced than that of cisplatin (IC₅₀: 12.4 ± 1.2 μM). The [ONON] type Ti^(IV) complexes slowly released nontoxic phenolato ligands in presence of large amount of aqueous media, and a fast cellular uptake process was proposed for these Ti^(IV) complexes based on metal uptake analysis. Decagram scale synthesis indicates this facile synthetic methodology can be applied to large scale synthesis.