Synthesis and characterization of copper(II) complexes of pyridine-2-carboxamidrazones as potent antimalarial agents

A Review of the Biological Activity of Amidrazone Derivatives

Amidrazones are widely used in chemical synthesis, industry and agriculture. We compiled some of the most important findings on the biological activities of amidrazones described in the years 2010-2022. The data were obtained using the ScienceDirect, Reaxys and Google Scholar search engines with keywords (amidrazone, carbohydrazonamide, carboximidohydrazide, aminoguanidine) and structure strategies. Compounds with significant biological activities were included in the review. The described structures derived from amidrazones include: amidrazone derivatives; aminoguanidine derivatives; complexes obtained using amidrazones as ligands; and some cyclic compounds obtained from amidrazones and/or containing an amidrazone moiety in their structures. This review includes chapters based on compound activities, including: tuberculostatic, antibacterial, antifungal, antiparasitic, antiviral, anti-inflammatory, cytoprotective, and antitumor compounds, as well as furin and acetylocholinesterase inhibitors. Detailed information on the compounds tested in vivo, along the mechanisms of action and toxicity of the selected amidrazone derivatives, are described. We describe examples of compounds that have a chance of becoming drugs due to promising preclinical or clinical research, as well as old drugs with new therapeutic targets (repositioning) which have the potential to be used in the treatment of other diseases. The described examples prove that amidrazone derivatives are a potential source of new therapeutic substances and deserve further research.

Copper (I)-Chloroquine Complexes: Interactions with DNA and Ferriprotoporphyrin, Inhibition of β-Hematin Formation and Relation to Antimalarial Activity

A new Cu(I)-chloroquine (CQ) complex [Cu(CQ)(PPh₃)₂]NO₃ (1) was synthesized and characterized, and its mechanism of action studied concomitant with the previously reported complex [Cu(CQ)₂]Cl (2). These copper (I) coordination compounds can be considered as potential antimalarial agents because they show better inhibition of the CQ-resistant strain in in vitro studies than CQ alone. In comparison with other metal-CQ complexes, only the gold complex was similar to (1), i.e., more active than CQ against both CQ-susceptible (3D7) and CQ-resistant strains (W2). These two copper (I)-compounds also demonstrated higher antiplasmodial activity against W2 than other copper complexes reported to date. This suggests that the incorporation of the copper metal center enhanced the biological activity of CQ. To better understand their significant growth inhibition of the Plasmodium falciparum parasite, the interaction with two essential molecular targets for the survival and proliferation of the malarial parasite were studied. These were the ferriprotoporphyrin group and the DNA, both important targets for current antimalarial drugs at the asexual erythrocytic stages. Both compounds (1,2) exhibited significant interactions with these targets. In particular, interactions with the DNA were dominated by the intercalator properties of the CQ ligand but may have also been affected by the presence of copper. Overall, these compounds were better parasitic inhibitors than chloroquine diphosphate (CQDP) alone or other previously reported metal-CQ complexes such as platinum, ruthenium and gold.

Novel Copper-Containing Cytotoxic Agents Based on 2-Thioxoimidazolones

A series of 73 ligands and 73 of their Cu⁺² and Cu⁺¹ copper complexes with different geometries, oxidation states of the metal, and redox activities were synthesized and characterized. The aim of the study was to establish the structure-activity relationship within a series of analogues with different substituents at the N(3) position, which govern the redox potentials of the Cu⁺²/Cu⁺¹ redox couples, ROS generation ability, and intracellular accumulation. Possible cytotoxicity mechanisms, such as DNA damage, DNA intercalation, telomerase inhibition, and apoptosis induction, have been investigated. ROS formation in MCF-7 cells and three-dimensional (3D) spheroids was proven using the Pt-nanoelectrode. Drug accumulation and ROS formation at 40-60 μm spheroid depths were found to be the key factors for the drug efficacy in the 3D tumor model, governed by the Cu⁺²/Cu⁺¹ redox potential. A nontoxic in vivo single-dose evaluation for two binuclear mixed-valence Cu⁺¹/Cu⁺² redox-active coordination compounds, 72k and 61k, was conducted.

Copper Coordination Compounds as Biologically Active Agents

Copper-containing coordination compounds attract wide attention due to the redox activity and biogenicity of copper ions, providing multiple pathways of biological activity. The pharmacological properties of metal complexes can be fine-tuned by varying the nature of the ligand and donor atoms. Copper-containing coordination compounds are effective antitumor agents, constituting a less expensive and safer alternative to classical platinum-containing chemotherapy, and are also effective as antimicrobial, antituberculosis, antimalarial, antifugal, and anti-inflammatory drugs. 64Сu-labeled coordination compounds are promising PET imaging agents for diagnosing malignant pathologies, including head and neck cancer, as well as the hallmark of Alzheimer's disease amyloid-β (Aβ). In this review article, we summarize different strategies for possible use of coordination compounds in the treatment and diagnosis of various diseases, and also various studies of the mechanisms of antitumor and antimicrobial action.

Synthesis and Characterization of Cu(II) and Mixed-Valence Cu(I)Cu(II) Clusters Supported by Pyridylamide Ligands

A group of copper complexes supported by polydentate pyridylamide ligands H₂bpda and H₂ppda were synthesized and characterized. The two Cu(II) dimers [Cu^II₂(Hbpda)₂(ClO₄)₂] (1) and [Cu^II₂(ppda)₂(DMF)₂] (2) were constructed by using neutral ligands to react with Cu(II) salts. Although the dimers showed similar structural features, the second-sphere interactions affect the structures differently. With the application of Et₃N, the tetranuclear cluster (HNEt₃)[Cu^II₄(bpda)₂(μ₃-OH)₂(ClO₄)(DMF)₃](ClO₄)₂ (3) and hexanuclear cluster (HNEt₃)₂[Cu^II₆(ppda)₆(H₂O)₂(CH₃OH)₂](ClO₄)₂ (4) were prepared under similar reaction conditions. The symmetrical and unsymmetrical arrangement of the ligand donors in ligands H₂bpda and H₂ppda led to the dramatic conformation difference of the two Cu(II) complexes. As part of our effort to explore mixed-valence copper chemistry, the triple-decker pentanuclear cluster [Cu^II₃Cu^I₂(bpda)₃(μ₃-O)] (5) was prepared. XPS examination demonstrated the localized mixed-valence properties of complex 5. Magnetic studies of the clusters with EPR evidence showed either weak ferromagnetic or antiferromagnetic interactions among copper centers. Due to the trigonal-planar conformation of the trinuclear Cu(II) motif with the μ₃-O center, complex 5 exhibits geometric spin frustration and engages in antisymmetric exchange interactions. DFT calculations were also performed to better interpret spectroscopic evidence and understand the electronic structures, especially the mixed-valence nature of complex 5.

A Perspective - can copper complexes be developed as a novel class of therapeutics?

Although copper-ligand complexes appear to be promising as a new class of therapeutics, other than the family of copper(ii) coordination compounds referred to as casiopeínas these compounds have yet to reach the clinic for human use. The pharmaceutical challenges associated with developing copper-based therapeutics will be presented in this article along with a discussion of the potential for high-throughput chemistry, computer-aided drug design, and nanotechnology to address the development of this important class of drug candidates.

Crystal structures of N'-amino-pyridine-2-carboximidamide and N'-{[1-(pyridin-2-yl)ethyl-idene]amino}-pyridine-2-carboximidamide

The crystal structures of N'-amino-pyridine-2-carboximidamide (C6H8N4), 1, and N'-{[1-(pyridin-2-yl)ethyl-idene]amino}-pyridine-2-carboximidamide (C13H13N5), 2, are described. The non-H atoms in compound 1 are nearly planar (r.m.s. deviation from planarity = 0.0108 Å), while 2 is twisted about the central N-N bond by 17.8 (2)°. Both mol-ecules are linked by inter-molecular N-H⋯N hydrogen-bonding inter-actions; 1 forms a two-dimensional hydrogen-bonding network and for 2 the network is a one-dimensional chain. The bond lengths of these mol-ecules are similar to those in other literature reports of azine and di-imine systems.

Novel metalloantimalarials: Transmission blocking effects of water soluble Cu(I), Ag(I) and Au(I) phosphane complexes on the murine malaria parasite Plasmodium berghei

The water soluble phosphane complexes [M(L)₄]PF₆ (M=Cu(I), Ag(I)) and [Au(L)₄]Cl (L=thp (tris(hydroxymethyl)phosphane) or PTA (1,3,5-triaza-7-phosphaadamantane)) showed notable in vitro activity against Plasmodium early sporogonic stages, the sexual forms of the malaria parasite that are responsible for infection of the mosquito vector. Effects varied according to both, the type of metal and phosphane ligands. [Ag(thp)₄]PF₆ was the best performing complex exhibiting a half inhibitory concentration (IC₅₀) value in the low micromolar range (0.3-15.6μM). The silver complex [Ag(thp)₄]PF₆ was characterized by X-ray crystallography revealing that the structure comprises the cationic complex [Ag(thp)₄]⁺, the PF₆^- anion, and a water molecule of crystallization. Our results revealed that Cu(I), Ag(I) and Au(I) phosphanes complexes elicited similar activity profiles showing potential for the development of antimalarial, transmission blocking compounds. Molecules targeting the sexual parasite stages in the human and/or mosquito host are urgently needed to complement current artemisinin based treatments and next generation antimalarials in a vision not only to cure the disease but to interrupt its transmission.

Antimalarial, antimicrobial, cytotoxic, DNA interaction and SOD like activities of tetrahedral copper(II) complexes

The mononuclear copper(II) complexes with P, O-donor ligand and different fluoroquinolones have been synthesized and characterized by elemental analysis, electronic spectra, TGA, EPR, FT-IR and LC-MS spectroscopy. An antimicrobial efficiency of the complexes has been tested against five different microorganisms in terms of minimum inhibitory concentration (MIC) and displays very good antimicrobial activity. The binding strength and binding mode of the complexes with Herring Sperm DNA (HS DNA) have been investigated by absorption titration and viscosity measurement studies. The studies suggest the classical intercalative mode of DNA binding. Gel electrophoresis assay determines the ability of the complexes to cleave the supercoiled form of pUC19 DNA. Synthesized complexes have been tested for their SOD mimic activity using nonenzymatic NBT/NADH/PMS system and found to have good antioxidant activity. All the complexes show good cytotoxic and in vitro antimalarial activities.

Copper complexes as therapeutic agents

The importance of transition metals in biological processes has been well established. Copper (Cu) is a transition metal that can exist in oxidised and reduced states. This allows it to participate in redox and catalytic chemistry, making it a suitable cofactor for a diverse range of enzymes and molecules. Cu deficiency or toxicity is implicated in a variety of pathological conditions; therefore inorganic complexes of Cu have been investigated for their therapeutic and diagnostic potential. These Cu complexes have been shown to be effective in cancer treatment due to their cytotoxic action on tumour cells. Alternatively, Cu complexes can also modulate Cu homeostasis in the brain, resulting in protective effects in several models of neurodegeneration. In other diseases such as coronary heart disease and skin disease, the success of Cu complexes as potential therapeutics will most likely be due to their ability to increase SOD activity, leading to relief of oxidative stress. This review seeks to provide a broad insight into some of the diverse actions of Cu complexes and demonstrate the strong future for these compounds as potential therapeutic agents.

Synthesis and Antiplasmodial Activity of 4-Alkylidene(arylidene)hydrazono-1,3-oxazinan-2-ones and 3-Hydroxy-N'-alkylidene(arylidene)propanehydrazonamides

Previously unreported 6-substituted 4-alkylidene(arylidene)hydrazono-1,3-oxazinan-2-ones and a series of open-chained 3-hydroxy-N′-alkylidene(arylidene)propanehydrazonamides were synthesized and evaluated for their in vitro antiplasmodial activity. The most active 3-hydroxy-N′-alkylidene(arylidene)propanehydrazonamide exhibits potent in vitro antiplasmodial activity against the chloroquine-sensitive strain 3D7 of Plasmodium falciparum and demonstrates an IC50 value of 0.2 µM.

Antimalarial evaluation of copper(II) nanohybrid solids: inhibition of plasmepsin II, a hemoglobin-degrading malarial aspartic protease from Plasmodium falciparum

A new class of copper(II) nanohybrid solids, LCu(CH(3)COO)(2) and LCuCl(2), have been synthesized and characterized by transmission electron microscopy, dynamic light scattering, and IR spectroscopy, and have been found to be capped by a bis(benzimidazole) diamide ligand (L). The particle sizes of these nanohybrid solids were found to be in the ranges 5-10 and 60-70 nm, respectively. These nanohybrid solids were evaluated for their in vitro antimalarial activity against a chloroquine-sensitive isolate of Plasmodium falciparum (MRC 2). The interactions between these nanohybrid solids and plasmepsin II (an aspartic protease and a plausible novel target for antimalarial drug development), which is believed to be essential for hemoglobin degradation by the parasite, have been assayed by UV-vis spectroscopy and inhibition kinetics using Lineweaver-Burk plots. Our results suggest that these two compounds have antimalarial activities, and the IC(50) values (0.025-0.032 microg/ml) are similar to the IC(50) value of the standard drug chloroquine used in the bioassay. Lineweaver-Burk plots for inhibition of plasmepsin II by LCu(CH(3)COO)(2) and LCuCl(2) show that the inhibition is competitive with respect to the substrate. The inhibition constants of LCu(CH(3)COO)(2) and LCuCl(2) were found to be 10 and 13 microM, respectively. The IC(50) values for inhibition of plasmepsin II by LCu(CH(3)COO)(2) and LCuCl(2) were found to be 14 and 17 microM, respectively. Copper(II) metal capped by a benzimidazole group, which resembles the histidine group of copper proteins (galactose oxidase, beta-hydroxylase), could provide a suitable anchoring site on the nanosurface and thus could be useful for inhibition of target enzymes via binding to the S1/S3 pocket of the enzyme hydrophobically. Both copper(II) nanohybrid solids were found to be nontoxic against human hepatocellular carcinoma cells and were highly selective for plasmepsin II versus human cathepsin D. The pivotal mechanism of antimalarial activity of these compounds via plasmepsin II inhibition in the P. falciparum malaria parasite is demonstrated.

Review on supermolecules as chemical drugs

Supramolecular medicinal chemistry field has been a quite rapidly developing, increasingly active and newly rising interdiscipline which is the new expansion of supramolecular chemistry in pharmaceutical sciences, and is gradually becoming a relatively independent scientific area. Supramolecular drugs could be defined as medicinal supermolecules formed by two or more molecules through non-covalent bonds. So far a lot of supermolecules as chemical drugs have been widely used in clinics. Supermolecules as chemical drugs, i.e. supramolecular chemical drugs or supramolecular drugs, which might have the excellences of lower cost, shorter period, higher potential as clinical drugs for their successful research and development, may possess higher bioavailability, better biocompatibility and drug-targeting, fewer multidrug-resistances, lower toxicity, less adverse effect, and better curative effects as well as safety, and therefore exhibit wide potential application. These overwhelming advantages have drawn enormous special attention. This paper gives the definition of supramolecular drugs, proposes the concept of supramolecular chemical drugs, and systematically reviews the recent advances in the research and development of supermolecules, including organic and inorganic complex ones as chemical drugs in the area of antitumor, anti-inflammatory, analgesic, antimalarial, antibacterial, antifungal, antivirus, anti-epileptic, cardiovascular agents and magnetic resonance imaging agents and so on. The perspectives of the foreseeable future and potential application of supramolecules as chemical drugs are also presented.