Cu(II) and Zn(II) Complexes of New 8-Hydroxyquinoline Schiff Bases: Investigating Their Structure, Solution Speciation, and Anticancer Potential

Anticancer activity of 8-hydroxyquinoline-triphenylphosphine rhodium(III) complexes targeting mitophagy pathways

Metallodrugs exhibiting distinct mechanisms of action compared with cisplatin hold promise for overcoming cisplatin resistance and improving the efficacy of anticancer drugs. In this study, a new series of rhodium (Rh)(III) complexes containing tris(triphenylphosphine)rhodium(I) chloride [(TPP)3RhCl] (TPP = triphenylphosphine, TPP=O = triphenylphosphine oxide) and 8-hydroxyquinoline derivatives (H-XR1-H-XR4), namely [Rh(XR1)2(TPP)Cl]·(TPP=O) (Yulin Normal University-1a [YNU-1a]), [Rh(XR2)2(TPP)Cl] (YNU-1b), [Rh(XR3)2(TPP)Cl] (YNU-1c), and [Rh(XR4)2(TPP)Cl] (YNU-1d), was synthesized and characterized via X-ray diffraction, mass spectrometry and IR. The cytotoxicity of the compounds YNU-1a-YNU-1d in Hep-G2 and HCC1806 human cancer cell lines and normal HL-7702 cell line was evaluated. YNU-1c exhibited cytotoxicity and selectivity in HCC1806 cells (IC50 = 0.13 ± 0.06 μM, selectivity factor (SF) = 384.6). The compounds YNU-1b and YNU-1c, which were selected for mechanistic studies, induced the activation of apoptotic pathways and mitophagy. In addition, these compounds released cytochrome c, cleaved caspase-3/pro-caspase-3 and downregulated the levels of mitochondrial respiratory chain complexes I/IV (M1 and M4) and ATP. The compound YNU-1c, which was selected for in vivo experiments, exhibited tumor growth inhibition (58.9 %). Importantly, hematoxylin and eosin staining and TUNEL revealed that HCC1806 tumor tissues exhibited significant apoptotic characteristics. YNU-1a-YNU-1d compounds are promising drug candidates that can be used to overcome cisplatin resistance.

Enhanced selectivity towards melanoma cells with zinc(II)-Schiff bases containing imidazole derivatives

Zinc(II)-complexes with the general formula [Zn(L)2] containing 8-hydroxyquinoline Schiff bases functionalized with 1-(3-aminopropyl)imidazole or 1-(3-aminopropyl)-2-methyl-1H-imidazole on 2-position and their respective ligands (HL1 or HL2) were synthesized and characterized by NMR, UV-Vis, FTIR and CD spectroscopies as well as ESI-MS spectrometry. Single crystals of HL2 and [Zn(L1)2]n were analysed by SC-XRD. [Zn(L1)2]n shows a 1D polymeric chain structure of alternating Zn(II) cations and bridging Schiff base ligands, in contrast to previously reported monomeric structures of analogous complexes. DFT calculations were performed to rationalize the polymeric X-ray structure of Zn(L1)2. Results showed that the ligands can bind as bi- or tridentate to Zn(II) and there is the possibility of a dynamic behavior for the complexes in solution. Both ligands and complexes present limited stability in aqueous media, however, in the presence of bovine serum albumin the complexes are stable. Molecular docking simulations and circular dichroism spectroscopic studies suggest binding to this protein in close proximity to the Trp213 residue. Biological studies on a panel of cancer cells revealed that the Zn(II)-complexes have a lower impact on cell viability than cisplatin, except for triple-negative breast cancer cells in which they were comparable. Notwithstanding, they display much higher selectivity towards cancer cells vs. normal cells, than cisplatin. They induce the generation of ROS and DNA double-strand breaks, primarily through apoptosis as the mode of cell death. Overall, the novel Zn(II)-complexes demonstrate improved induction of apoptosis and higher selectivity, particularly for melanoma cells, compared to previously reported analogues, making them promising candidates for clinical application.

Synthesis of chiral Cu(II) complexes from pro-chiral Schiff base ligand and investigation of their catalytic activity in the asymmetric synthesis of 1,2,3-triazoles

A pro-chiral Schiff base ligand (HL) was synthesized by the reaction of 2-amino-2-ethyl-1,3-propanediol and pyridine-2-carbaldehyde in methanol. The reaction of HL with CuCl2·2H2O and CuBr2 in methanol gave neutral mononuclear Cu(II) complexes with general formula of [Cu(HL)Cl2] (1) and [Cu(HL)Br2] (2), respectively. By slow evaporation of the methanolic solutions of 1 and 2, their enantiomers were isolated in crystalline format. The formation of pure chiral crystals in the racemic mixture was amply authenticated by single crystal X-ray analysis, which indicated that S-[Cu(HL)Cl2], R-[Cu(HL)Cl2], and S-[Cu(HL)Br2] are crystallized in chiral P212121 space group of orthorhombic system. Preferential crystallization was used to isolate the R and S enantiomers as single crystals and the isolated compounds were also studied by CD analysis. Structural studies indicated that the origin of the chirality in these compounds is related to the coordination mode of the employed pro-chiral ligand (HL) because one of its carbon atoms has been converted to a chiral center in the synthesized complexes. Subsequently, these complexes were used in click synthesis of a β-hydroxy-1,2,3-triazole and the results of catalytic studies indicated that 1 and 2 can act as enantioselective catalysts for the asymmetric synthesis of β-hydroxy-1,2,3-triazole product under mild condition. This study illustrates the significant capacity of the use of pro-chiral ligands in preparing chiral catalysts based on complexes which can also be considered as an effective approach to cheap chiral catalysts from achiral reagents.

Synthesis, characterization, and cancer cell-selective cytotoxicity of mixed-ligand cobalt(III) complexes of 8-hydroxyquinolines and phenanthroline bases

Transition metal complexes exhibiting selective toxicity towards a broad range of cancer types are highly desirable as potential anticancer agents. Herein, we report the synthesis, characterization, and cytotoxicity studies of six new mixed-ligand cobalt(III) complexes of general formula [Co(B)2(L)](ClO4)2 (1-6), where B is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), and L is the monoanion of 8-hydroxyquinoline (HQ in 1, 3, 5) and 5-chloro-7-iodo-8-hydroxyquinoline (CQ in 2, 4, 6). The X-ray single crystal structures of complexes 1 and 2 as PF6- salts revealed a distorted octahedral CoN5O coordination environment. Complexes demonstrated good stability in an aqueous buffer medium and in the presence of ascorbic acid as a reductant. Cytotoxicity studies using a panel of nine cancer cell lines showed that complex 6, with the dppz and CQ ligands, was significantly toxic against most cancer cell types, yielding IC50 values in the range of 2 to 14 μM. Complexes 1, 3, and 5, containing the HQ ligand, displayed lower toxicity compared to their CQ counterparts. The phenanthroline complexes demonstrated marginal toxicity towards the tested cell lines, while the dpq complexes exhibited moderate toxicity. Interestingly, all complexes demonstrated negligible toxicity towards normal HEK-293 kidney cells (IC50 > 100 μM). The observed cytotoxicity of the complexes correlated well with their lipophilicities (dppz > dpq > phen). The cytotoxicity of complex 6 was comparable to that of the clinical drug cisplatin under similar conditions. Notably, neither the HQ nor the CQ ligands alone demonstrated noticeable toxicity against any of the tested cell lines. The Annexin-V-FITC and DCFDA assays revealed that the cell death mechanism induced by the complexes involved apoptosis, which could be attributed to the metal-assisted generation of reactive oxygen species. Overall, the dppz complex 6, with its remarkable cytotoxicity against a broad range of cancer cells and negligible toxicity toward normal cells, holds significant potential for cancer chemotherapeutic applications.

First-Row Transition 7-Oxo-5-phenyl-1,2,4-triazolo[1,5-a]pyrimidine Metal Complexes: Antiparasitic Activity and Release Studies

Leishmaniasis and Chagas disease are still considered neglected illnesses due to the lack of investment in research, despite the fact that almost one million new cases are reported every year. Four 7-oxo-5-phenyl-1,2,4-triazolo[1,5-a]pyrimidine (HftpO) first-row transition complexes (Cu, Co, Ni, Zn) have been studied for the first time in vitro against five different species of Leishmania spp. (L. infantum, L. braziliensis, L. donovani, L. peruviana and L. mexicana) as well as Trypanosoma cruzi, showing higher efficacy than the reference commercial drugs. UV and luminescence properties were also evaluated. As a proof of concept, anchoring of a model high-effective-metal complex as an antiparasitic agent on silica nanoparticles was carried out for the first time, and drug-release behaviour was evaluated, assessing this new approach for drug vehiculation.

Synthesis of Cu (II) and Zn (II) Complexes of a Quinoline Based Flexible Amide Receptor as Fluorescent Probe for Dihydrogen Phosphate and Hydrogen Sulphate and Their Antibacterial Activity

A novel 8-hydroxy quinoline-derived amide receptor, in conjunction with its Cu (II) and Zn (II) complexes, has been strategically developed to function as remarkably efficient fluorescent receptors with a distinct capability for anion sensing. The comprehensive characterization of the synthesized compounds were achieved through UV-Vis, IR, NMR, and HRMS spectroscopic techniques. Among the Cu (II) and Zn (II) complexes, the latter exhibits superior selectivity for anions, specifically dihydrogen phosphate and hydrogen sulfate, as their tetrabutylammonium salts in a 9:1 acetonitrile-water (v/v) mixture. The Cu (II) complex demonstrates enhanced anion binding compared to the amide ligand, albeit with reduced selectivity. Furthermore, the affinity was evaluated using the Benesi-Hildebrand plot. The binding constants and Limit of Detection (LOD) for both complexes were precisely quantified. The Job plot illustrates a clear 1:1 binding interaction between the metal complexes and the guest anions. Significantly, both metal-complex receptors display a broad spectrum of antibacterial activity, against both gram-positive and gram-negative bacteria. It is worth highlighting that the Zn (II) complexed receptor outperforms the Cu (II) complexed receptor, as evidenced by its considerably lower Minimum Inhibitory Concentration (MIC) value against both bacterial strains.