Synthesis, characterization and pharmacological evaluation of ferrocenyl azines and their rhodium(I) complexes

Synthesis, antimicrobial activity, antioxidant activity and molecular docking of novel chitosan derivatives containing glycine Schiff bases as potential succinate dehydrogenase inhibitors

Succinate dehydrogenase (SDH) is an important inner mitochondrial membrane-bound enzyme involved in redox reactions during the tricarboxylic acid cycle. Therefore, a series of novel chitosan derivatives were designed and synthesized as potential microbicides targeting SDH and precisely characterized by FTIR, 1H NMR and SEM. Their antifungal and antibacterial activities were evaluated against Botrytis cinerea, Fusarium graminearum, Staphylococcus aureus and Escherichia coli. The bioassays revealed that these chitosan derivatives exerted significant antifungal effects, with four of the compounds achieving 100 % inhibition of Fusarium graminearum merely at a concentration of 0.5 mg/mL. Additionally, CSGDCH showed 79.34 % inhibition of Botrytis cinerea at a concentration of 0.1 mg/mL. In vitro antibacterial tests revealed that CSGDCH and CSGDBH have excellent Staphylococcus aureus and Escherichia coli inhibition with MICs of 0.0156 mg/mL and 0.03125 mg/mL, respectively. Molecular docking studies have been carried out to explore the binding energy and binding mode of chitosan and chitosan derivatives with SDH. The analyses indicated that chitosan derivatives targeted the active site of the SDH protein more precisely, disrupting its normal function and ultimately repressing the growth of microbial cells. Furthermore, the chitosan derivatives were also evaluated biologically for antioxidation, and all of these compounds had a greater degree of reducing power, superoxide radical, hydroxyl radical and DPPH-radical scavenging activity than chitosan. This research has the potential for the development of agricultural antimicrobial agents.

Transition Metal Complexes as Antimalarial Agents: A Review

In antimalarial drug development research, overcoming drug resistance has been a major challenge for researchers. Nowadays, several drugs like chloroquine, mefloquine, sulfadoxine, and artemisinin are used to treat malaria. But increment in drug resistance has pushed researchers to find novel drugs to tackle drug resistance problems. The idea of using transition metal complexes with pharmacophores as ligands/ligand pendants to show enhanced antimalarial activity with a novel mechanism of action has gained significant attention recently. The advantages of metal complexes include tunable chemical/physical properties, redox activity, avoiding resistance factors, etc. Several recent reports have successfully demonstrated that the metal complexation of known organic antimalarial drugs can overcome drug resistance by showing enhanced activities than the parent drugs. This review has discussed the fruitful research works done in the past few years falling into this criterion. Based on transition metal series (3d, 4d, or 5d), the antimalarial metal complexes have been divided into three broad categories (3d, 4d, or 5d metal-based), and their activities have been compared with the similar control complexes as well as the parent drugs. Furthermore, we have also commented on the potential issues and their possible solution for translating these metal-based antimalarial complexes into the clinic.

Recent Advances in the Biological Investigation of Organometallic Platinum-Group Metal (Ir, Ru, Rh, Os, Pd, Pt) Complexes as Antimalarial Agents

In the face of the recent pandemic and emergence of infectious diseases of viral origin, research on parasitic diseases such as malaria continues to remain critical and innovative methods are required to target the rising widespread resistance that renders conventional therapies unusable. The prolific use of auxiliary metallo-fragments has augmented the search for novel drug regimens in an attempt to combat rising resistance. The development of organometallic compounds (those containing metal-carbon bonds) as antimalarial drugs has been exemplified by the clinical development of ferroquine in the nascent field of Bioorganometallic Chemistry. With their inherent physicochemical properties, organometallic complexes can modulate the discipline of chemical biology by proffering different modes of action and targeting various enzymes. With the beneficiation of platinum group metals (PGMs) in mind, this review aims to describe recent studies on the antimalarial activity of PGM-based organometallic complexes. This review does not provide an exhaustive coverage of the literature but focusses on recent advances of bioorganometallic antimalarial drug leads, including a brief mention of recent trends comprising interactions with biomolecules such as heme and intracellular catalysis. This resource can be used in parallel with complementary reviews on metal-based complexes tested against malaria.

The in Vitro Antiplasmodial and Antiproliferative Activity of New Ferrocene-Based α-Aminocresols Targeting Hemozoin Inhibition and DNA Interaction

The conjugation of organometallic complexes to known bioactive organic frameworks is a proven strategy revered for devising new drug molecules with novel modes of action. This approach holds great promise for the generation of potent drug leads in the quest for therapeutic chemotypes with the potential to overcome the development of clinical resistance. Herein, we present the in vitro antiplasmodial and antiproliferative investigation of ferrocenyl α-aminocresol conjugates assembled by amalgamation of the organometallic ferrocene unit and an α-aminocresol scaffold possessing antimalarial activity. The compounds pursued in the study exhibited higher toxicity towards the chemosensitive (3D7) and -resistant (Dd2) strains of the Plasmodium falciparum parasite than to the human HCC70 triple-negative breast cancer cell line. Indication of cross-resistance was absent for the compounds evaluated against the multi-resistant Dd2 strain. Structure-activity analysis revealed that the phenolic hydroxy group and rotatable σ bond between the α-carbon and NH group of the α-amino-o-cresol skeleton are crucial for the biological activity of the compounds. Spectrophotometric techniques and in silico docking simulations performed on selected derivatives suggest that the compounds show a dual mode of action involving hemozoin inhibition and DNA interaction via minor-groove binding. Lastly, compound 9 a, identified as a possible lead, exhibited preferential binding for the plasmodial DNA isolated from 3D7 P. falciparum trophozoites over the mammalian calf thymus DNA, thereby substantiating the enhanced antiplasmodial activity of the compounds. The presented research demonstrates the strategy of incorporating organometallic complexes into known biologically active organic scaffolds as a viable avenue to fashion novel multimodal compounds with potential to counter the development drug resistance.

Ferrocene-containing hybrids as potential anticancer agents: Current developments, mechanisms of action and structure-activity relationships

Cancer is one of the most fatal threatens to human health throughout the world. The major challenges in the control and eradication of cancers are the continuous emergency of drug-resistant cancer and the low specificity of anticancer agents, creating an urgent need to develop novel anticancer agents. Organometallic compounds especially ferrocene derivatives possess remarkable structural and mechanistic diversity, inherent stability towards air, heat and light, low toxicity, low cost, reversible redox, ligand exchange, and catalytic properties, making them promising drug candidates for cancer therapy. Ferrocifen, a ferrocene-phenol hybrid, has demonstrated promising anticancer properties on drug-resistant cancers. Currently, Ferrocifen is in pre-clinical trial against cancers. Obviously, ferrocene moiety is a useful template for the development of novel anticancer agents. This review will provide an overview of ferrocene-containing hybrids with potential application in the treatment of cancers covering articles published between 2010 and 2020. The mechanisms of action, the critical aspects of design and structure-activity relationships are also discussed.

Repurposing a polymer precursor: Synthesis and in vitro medicinal potential of ferrocenyl 1,3-benzoxazine derivatives

Cancer and malaria remain relevant pathologies in modern medicinal chemistry endeavours. This is compounded by the threat of development of resistance to existing clinical drugs in use as first-line option for treatment of these diseases. To counter this threat, strategies such as drug repurposing and hybridization are constantly adapted in contemporary drug discovery for the expansion of the drug arsenal and generation of novel chemotypes with potential to avert or delay resistance. In the present study, a polymer precursor scaffold, 1,3-benzoxazine, has been repurposed by incorporation of an organometallic ferrocene unit to produce a novel class of compounds showing in vitro biological activity against breast cancer, malaria and trypanosomiasis. The resultant ferrocenyl 1,3-benzoxazine compounds displayed high potency and selectivity against the investigated diseases, with IC₅₀ values in the low and sub-micromolar range against both chloroquine-sensitive (3D7) and resistant (Dd2) strains of the Plasmodium falciparum parasite. On the other hand, antitrypanosomal (Trypanosoma brucei brucei) potencies were observed between 0.15 and 38.6 μM. The majority of the compounds were not active against breast cancer cells (HCC70), however, for the toxic compounds, IC₅₀ values ranged from 11.0 to 30.5 μM. Preliminary structure-activity relationships revealed the basic oxazine sub-ring and lipophilic benzene substituents to be conducive for biological efficacy of the ferrocenyl 1,3-benzoxazines reported in the study. DNA interaction studies performed on the most promising compound 4c suggested that DNA damage may be one possible mode of action of this class of compounds.

Crystal structures and Hirshfeld surface analysis of four 1,4-bis(methoxyphenyl)-2,3-diazabuta-1,3-dienes: comparisons of the intermolecular interactions in related compounds

The crystal structures of four azines, namely 1-3-bis(4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 1, 1,3-bis(2,3-dimethoxyphenyl)-2,3-diaza-1,4-butadiene, 2, 1,3-bis(2-hydroxy-3-methoxyphenyl)-2,3-diaza-1,4-butadiene, 3, and 1,3-bis(2-hydroxy-4-methoxyphenyl)-2,3-diaza-1,4-butadiene, 4, are reported. Molecules of 3 and 4, and both independent molecules of 2, Mol A and Mol B, possess inversion centers. The central C=N–N=C units in each molecule is planar with an (E,E) conformation. The intermolecular interactions found in the four compounds are C–H···O, C–H–N, C–H---π and π---π interactions. However, there is no consistent set of intermolecular interactions for the four compounds. Compound, 1, has a two-dimensional undulating sheet structure, generated from C–H···O and C–H···N intermolecular hydrogen bonds. The only recognized intermolecular interaction in 2 is a C–H···O hydrogen bond, which results in a zig-zag chain of alternating molecules, Mol A and Mol B. While 3 forms a puckered sheet of molecules, solely via C–H···π interactions, its isomeric compound, 4, has a more elaborate three-dimensional structure generated from a combination of C–H···O hydrogen bonds, C–H···π and π···π interactions.

The findings in this study, based on both PLATON and Hirshfeld approaches, for the four representative compounds match well the reported structural findings in the literature of related compounds, which are based solely on geometric parameters.

Crystal structures and Hirshfeld surface analyses of halogen substituted azine derivatives, 1,4-bis(halophenyl)-2,3-diazabuta-1,3-dienes

The crystal structures and Hirshfeld surface analyses are reported, from data collected at 100 K, of six 1,4-bis(X,Y-phenyl)-2,3-diazabuta-1,3-dienes (1–6), namely (1: X, Y=H, 4-Cl; 2: X, Y=3,4-Cl2; 3: X, Y=2,4-Cl2; 4: X, Y=H, 2-Br, H; 5: X, Y=H, 3-Br; 6: X, Y=H, 4-Br. The six halogen derivatives crystallise in the monoclinic group P21/c. In each case, the asymmetric unit is one half of the molecule, with the molecules lying across inversion centres, midway between the N–N bonds, with the central C–C=N–N=C–C fragments having all transoid conformations. Each of the six molecules deviates a little from overall planarity. The π···π stacking interactions are the most important intermolecular interactions in each of the six compounds. In the cases of 3 and 4, the π···π stacks are augmented by additional C–X···π (X=Cl or Br) interactions, while in 4, the π···π stacks are linked by weak Br···Br interactions, and in 3, weak Cl···Cl contacts are considered to be also involved in cementing the supra molecular arrangements. The short separations of the layers within the stacks and the extent of the overlaps of the π systems point to significant strengths of the π···π interactions. Comparisons with published structures of related chloro and fluoro compounds indicated similar results: related iodo derivatives, IC6H4CH=N–N=CHC6H4I do not possess as strong π···π interactions. The Hirshfeld analysis indicated further intermolecular contacts which fell outside the normal PLATON cutoff values.

Antimicrobial activity of organometallic isonicotinyl and pyrazinyl ferrocenyl-derived complexes

Isonicotinyl and pyrazinyl ferrocenyl-derived complexes were evaluatedin vitrofor antimycobacterial and antiparasitic activity.

Rhodium complexes as therapeutic agents

This perspective highlights recent examples of rhodium complexes that show diverse biological activities against various targets, including enzymes and protein–protein interactions.