Zinc(II) Complex with Pyrazolone-Based Hydrazones is Strongly Effective against Trypanosoma brucei Which Causes African Sleeping Sickness

Zinc from an Essential Element to an Antiparasitic Therapeutic Agent

Tropical parasitic diseases affect millions of people around the world, particularly in poor countries. The human parasitic diseases that will be covered in this review are malaria and neglected diseases, such as leishmaniasis, Chagas disease, and African trypanosomiasis. The current treatments for these diseases present several problems, such as the development of drug resistance, very limited drugs available in the clinic, significant side effects of the drugs, and a long treatment period. For these reasons, there is an urgent need to develop new chemotherapeutics to eradicate or eliminate these diseases. Zinc-based drugs against parasitic diseases could be an alternative therapy to overcome the difficulties of the approved metallodrugs as antiparasitic agents. Zinc-based drugs are becoming an exciting field of research because zinc is an essential element that can lead to the development of multitarget antiparasitic agents, which are reviewed here.

Tandem Deacetalization-Knoevenagel Condensation Reactions for the Synthesis of Benzylidene Malononitrile Using Ruthenium(II) Cymene Complexes

In this study, we report the synthesis and full characterization of five novel ruthenium(II) cymene complexes with the general formula [Ru(cym)(L')Cl], featuring N,O- and N,N-coordinating pyrazolone-based hydrazone ligands. We have characterized these complexes using single X-ray crystallography, Fourier-transform infrared spectroscopy (FT-IR), Nuclear magnetic resonance (NMR), elemental analysis, and Electrospray Ionization Mass Spectroscopy (ESI-MS). Crystallographic analysis confirmed that all of the complexes have a similar type of half-sandwich, pseudo-octahedral "three-legged piano-stool" geometry where the cymene moiety displays the typical η6-coordination mode and the hydrazone ligands coordinate to the Ru(II) center in a bidentate fashion. These complexes, with multiple catalytic sites, demonstrated high efficiency in catalyzing one-pot cascade deacetalization-Knoevenagel condensation reactions under mild conditions, achieving up to 92% of final product yield at 75 °C after 4 h of reaction time under solvent-free condition. Additionally, DFT calculations provided insight into the catalytic mechanism, suggesting a pathway driven by metal-ligand cooperation, assisted by the basic oxygen site of the pyrazolone ring and by the weakly acidic character of the NNH proton of the hydrazone group.

Pyrazolone-Based Zn(II) Complexes Display Antitumor Effects in Mutant p53-Carrying Cancer Cells

The synthesis and characterization of nine Schiff bases of pyrazolone ligands HLn (n = 1-9) and the corresponding zinc(II) complexes 1-9 of composition [Zn(Ln)2] (n = 1-9) are reported. The molecular structures of complexes 2, 3, 4, 8, and 9 were determined by single-crystal X-ray diffraction analysis, highlighting in all cases a distorted tetrahedral geometry around the Zn(II) ion. Density functional theory studies are performed on both the HLn ligands and the derived complexes. A mechanism of dissociation and hydrolyzation of the coordinated Schiff base ligands is suggested, confirmed experimentally by powder X-ray diffraction study and photophysical studies. Complexes 1-9 were investigated in vitro as anticancer agents, along with mutant p53 (mutp53) protein levels in human cancer cell lines carrying R175H and R273H mutp53 proteins. Only those complexes with the highest Zn(II) ion release via dissociation have shown a significant cytotoxic activity with reduction of mutp53 protein levels.

De-epimerizing DyKAT of β-lactones generated by isothiourea-catalysed enantioselective [2 + 2] cycloaddition

An enantioselective isothiourea-catalysed [2 + 2] cycloaddition of C(1)-ammonium enolates with pyrazol-4,5-diones is used to construct spirocyclic β-lactones in good yields, excellent enantioselectivity (99 : 1 er) but with modest diastereocontrol (typically 70 : 30 dr). Upon ring-opening with morpholine or alternative nucleophilic amines and alcohols β-hydroxyamide and β-hydroxyester products are generated with enhanced diastereocontrol (up to >95 : 5 dr). Control experiments show that stereoconvergence is observed in the ring-opening of diastereoisomeric β-lactones, leading to a single product (>95 : 5 dr, >99 : 1 er). Mechanistic studies and DFT analysis indicate a substrate controlled Dynamic Kinetic Asymmetric Transformation (DyKAT) involving epimerisation at C(3) of the β-lactone under the reaction conditions, coupled with a hydrogen bond-assisted nucleophilic addition to the Si-face of the β-lactone and stereodetermining ring-opening. The scope and limitations of a one-pot protocol consisting of isothiourea-catalysed enantio-determining [2 + 2] cycloaddition followed by diastereo-determining ring-opening are subsequently developed. Variation within the anhydride ammonium enolate precursor, as well as N(1) and C(3) within the pyrazol-4,5-dione scaffold is demonstrated, giving a range of functionalised β-hydroxyamides with high diastereo- and enantiocontrol (>20 examples, up to >95 : 5 dr and >99 : 1 er) via this DyKAT.

8-hydroxyquinoline-N-oxide copper(II)- and zinc(II)-phenanthroline and bipyridine coordination compounds: Design, synthesis, structures, and antitumor evaluation

Fourteen novel tumor-targeting copper(II) and zinc(II) complexes, [Cu(ONQ)(QD1)(NO3)]·CH3OH (NQ3), [Cu(ONQ)(QD2)(NO3)] (NQ2), [Cu(NQ)(QD2)Cl] (NQ3), [Cu(ONQ)(QD1)Cl] (NQ4), [Cu(ONQ)(QD3)](NO3) (NQ5), [Cu(ONQ)(QD3)Cl] (NQ6), [Zn(ONQ)(QD4)Cl] (NQ7), [Zn(ONQ)(QD1)Cl] (NQ8), [Zn(ONQ)(QD5)Cl] (NQ9), [Zn(ONQ)(QD2)Cl] (NQ10), [Zn(ONQ)(QD6)Cl] (NQ11), [Zn(ONQ)(QD7)Cl] (NQ12), and [Zn(ONQ)(QD3)Cl] (NQ13) supported on 8-hydroxyquinoline-N-oxide (H-ONQ), 2,2'-dipyridyl (QD1), 5,5'-dimethyl-2,2'-bipyridyl (QD2), 1,10-phenanthroline (QD3), 4,4'-dimethoxy-2,2'-bipyridyl (QD4), 4,4'-dimethyl-2,2'-bipyridyl (QD5), 5-chloro-1,10-phenanthroline (QD6), and bathophenanthroline (QD7), were first synthesized and characterized using various spectroscopic techniques. Furthermore, NQ1-NQ13 exhibited higher antiproliferative activity and selectivity for cisplatin-resistant SK-OV-3/DDP tumor cells (CiSK3) compared to normal HL-7702 cells based on results obtained from the cell counting Kit-8 (CCK-8) assay. The complexation of copper(II) ion with QD2 and ONQ ligands resulted in an evident increase in the antiproliferation of NQ1-NQ6, with NQ6 exhibiting the highest antitumor potency against CiSK3 cells compared to NQ1-NQ5, H-ONQ, QD1-QD7, and NQ7-NQ13 as well as the reference cisplatin drug with an IC50 value of 0.17 ± 0.05 μM. Mechanistic studies revealed that NQ4 and NQ6 induced apoptosis of CiSK3 cells via mitophagy pathway regulation and adenosine triphosphate (ATP) depletion. Further, the differential induction of mitophagy decreased in the order of NQ6 > NQ4, which can be attributed to the major impact of the QD3 ligand with a large planar geometry and the Cl leaving group within the NQ6 complex. In summary, these results confirmed that the newly synthesized H-ONQ copper(II) and zinc(II) coordination metal compounds NQ1-NQ13 exhibit potential as anticancer drugs for cisplatin-resistant ovarian CiSK3 cancer treatment.

Design, Synthesis and Evaluation of a Series of Zinc(II) Complexes of Anthracene-Affixed Multifunctional Organic Assembly as Potential Antibacterial and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus

A novel class of zinc(II)-based metal complexes, i.e., [Zn₂(acdp)(μ-Cl)]·2H₂O (1), [Zn₂(acdp)(μ-NO₃)]·2H₂O (2), and [Zn₂(acdp)(μ-O₂CCF₃)]·2H₂O (3) (Cl^- = chloride; NO₃^- = nitrate; CF₃CO₂^- = trifluoroacetate) of anthracene-affixed multifunctional organic assembly, H₃acdp (H₃acdp = N,N'-bis[anthracene-2-ylmethyl]-N,N'-bis[carboxymethyl]-1,3-diaminopropan-2-ol), have emerged as promising antibacterial and antibiofilm agents in the domain of medicinal chemistry. Accordingly, complexes 1-3 were synthesized by utilizing H₃acdp in combination with ZnCl₂, Zn(NO₃)₂·6H₂O, and Zn(CF₃CO₂)₂·H₂O respectively, in the presence of NaOH at ambient temperature. The complexation between H₃acdp and Zn²⁺ was delineated by a combined approach of spectrophotometric and spectrofluorometric titration studies. The stoichiometry of acdp^3-/Zn²⁺ in all three complexes is observed to be 1:2, as confirmed by spectrophotometric/spectrofluorometric titration data. Elemental analysis (C, H, N, Zn), molar conductance, FTIR, UV-vis, and thermoanalytical (TGA/DTA) data were effectively used to characterize these complexes. Besides, the structures of 1-3 were established by density functional theory (DFT) calculation using B3LYP/6-311G, specifying a self-assembled compact geometry with average Zn···Zn separation of 3.4629 Å. All three zinc complexes exhibited significantly high antibacterial and antibiofilm activity against methicillin-resistant Staphylococcus aureus (MRSA BAA1717). However, complex 1 showed a more recognizable activity than 2 and 3, with minimum inhibitory concentration (MIC) values of 200, 350, and 450 μg/mL, respectively. The antimicrobial activity was tested by employing the minimum inhibitory concentration (MIC) and time-kill assay. The crystal violet (CV) assay and microscopic study were performed to examine the antibiofilm activity. As observed, complexes 1-3 had an effect on the production of extracellular polymeric substance (EPS), biofilm cell-viability, and other virulence factors such as staphyloxanthin and hemolysin production, autoaggregation ability, and microbial cell-surface hydrophobicity. Reactive oxygen species (ROS) generated due to inhibition of staphyloxanthin production in response to 1-3 were also analyzed. Moreover, complexes 1-3 showed an ability to damage the bacterial cell membrane due to accumulation of ROS resulting in DNA leakage. In addition, complexes 1-3 displayed a synergistic/additive activity with a commercially available antibiotic drug, vancomycin, with enhanced antibacterial activity. On the whole, our investigation disclosed that complex 1 could be a promising drug lead and attract much attention to medicinal chemists compared to 2 and 3 from therapeutic aspects.