Coordination compounds of heterocyclic bases: synthesis, characterization, computational and biological studies

An Insight into the Effect of Schiff Base and their d and f Block Metal Complexes on Various Cancer Cell Lines as Anticancer Agents: A Review

Over the last few decades, an alarming rise in the percentage of individuals with cancer and those with multi-resistant illnesses has forced researchers to explore possibilities for novel therapeutic approaches. Numerous medications currently exist to treat various disorders, and the development of small molecules as anticancer agents has considerable potential. However, the widespread prevalence of resistance to multiple drugs in cancer indicates that it is necessary to discover novel and promising compounds with ideal characteristics that could overcome the multidrug resistance issue. The utilisation of metallo-drugs has served as a productive anticancer chemotherapeutic method, and this approach may be implemented for combating multi-resistant tumours more successfully. Schiff bases have been receiving a lot of attention as a group of compounds due to their adaptable metal chelating abilities, innate biologic properties, and versatility to tweak the structure to optimise it for a specific biological purpose. The biological relevance of Schiff base and related complexes, notably their anticancer effects, has increased in their popularity as bio-inorganic chemistry has progressed. As a result of learning about Schiff bases antitumor efficacy against multiple cancer cell lines and their complexes, researchers are motivated to develop novel, side-effect-free anticancer treatments. According to study reports from the past ten years, we are still seeking a powerful anticancer contender. This study highlights the potential of Schiff bases, a broad class of chemical molecules, as potent anticancer agents. In combination with other anticancer strategies, they enhance the efficacy of treatment by elevating the cytotoxicity of chemotherapy, surmounting drug resistance, and promoting targeted therapy. Schiff bases also cause cancer cell DNA repair, improve immunotherapy, prevent angiogenesis, cause apoptosis, and lessen the side effects of chemotherapy. The present review explores the development of potential Schiff base and their d and f block metal complexes as anticancer agents against various cancer cell lines.

Recent insights into antibacterial potential of benzothiazole derivatives

Antimicrobial resistance (AMR) is a worldwide concern among infectious diseases due to increased mortality, morbidity and treatment cost. According to WHO 2019 report, among the 32 antibiotics in the clinical trials, only six were classified as innovative and containing novel moiety. The remaining antibiotics from this list contain previously known moiety (WHO AMR 2019). Therefore, the development of novel antibiotics to control resistance problems is crucial. Benzothiazole derivatives are of great interest due to their wide range of biological activities and medicinal applications. Reported data indicated that benzothiazole derivatives displayed antibacterial activity by inhibiting the dihydroorotase, DNA gyrase, uridine diphosphate-n-acetyl enol pyruvyl glucosamine reductase (MurB), peptide deformylase, aldose reductase, casdihydrofolate reductase, enoyl acyl carrier protein reductase, dialkylglycine decarboxylase, dehydrosqualene synthase, dihydropteroate synthase and tyrosine kinase. The present review analyzed the synthesis, structure-activity relationship (SAR) and mechanism of action studies of benzothiazole derivatives as antibacterial agents reported by various research groups in the last five years (2018-2022). Different patents on the antimicrobial activity of benzothiazole derivatives have also been summarized. The finding of the present review will be beneficial for the researchers in the development of novel antibacterial molecules based on benzothiazole moiety.

Graphical Abstract

Antimicrobial Activity of Rhenium Di- and Tricarbonyl Diimine Complexes: Insights on Membrane-Bound S. aureus Protein Binding

Antimicrobial resistance is one of the major human health threats, with significant impacts on the global economy. Antibiotics are becoming increasingly ineffective as drug-resistance spreads, imposing an urgent need for new and innovative antimicrobial agents. Metal complexes are an untapped source of antimicrobial potential. Rhenium complexes, amongst others, are particularly attractive due to their low in vivo toxicity and high antimicrobial activity, but little is known about their targets and mechanism of action. In this study, a series of rhenium di- and tricarbonyl diimine complexes were prepared and evaluated for their antimicrobial potential against eight different microorganisms comprising Gram-negative and -positive bacteria. Our data showed that none of the Re dicarbonyl or neutral tricarbonyl species have either bactericidal or bacteriostatic potential. In order to identify possible targets of the molecules, and thus possibly understand the observed differences in the antimicrobial efficacy of the molecules, we computationally evaluated the binding affinity of active and inactive complexes against structurally characterized membrane-bound S. aureus proteins. The computational analysis indicates two possible major targets for this class of compounds, namely lipoteichoic acids flippase (LtaA) and lipoprotein signal peptidase II (LspA). Our results, consistent with the published in vitro studies, will be useful for the future design of rhenium tricarbonyl diimine-based antibiotics.

Synthesis, Spectroscopic Analysis, and in Vitro/in Silico Biological Studies of Novel Piperidine Derivatives Heterocyclic Schiff-Mannich Base Compounds

In the present study, 3-substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (S1-8) were synthesized by treating 4-hydroxybenzaldehyde (B) with eight different 3-substitued-4-amino-4,5-dihydro-1H-1,2,4-triazole-5-ones (T1-8) in acetic acid medium, separately. The synthesized Schiff bases (S) were reacted with formaldehyde and secondary amine such as 4-piperidinecarboxyamide to afford novel heterocyclic bases. 3-Substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (T) were treated with 4-piperidinecarboxyamide in the presence of formaldehyde to synthesize eight new 1-(4-piperidinecarboxyamide-1-yl-methyl)-3-substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (M1-8). The structure characterization of compounds was carried out using ¹ H-NMR, IR, HR-MS, and ¹³ C-NMR spectroscopic methods. The inhibitory properties of the newly synthesized compounds were calculated against the acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and glutathione S-transferase (GST) enzymes. Ki values were calculated in the range of 20.06±3.11-36.86±6.17 μM for GST, 17.87±2.91-30.53±4.25 μM for AChE, 9.08±0.69-20.02±2.88 μM for BChE, respectively, Besides, IC₅₀ values were also calculated. Best binding scores of -inhibitors against used enzymes were calculated as -12.095 kcal/mol, -12.775 kcal/mol, and -9.336 kcal/mol, respectively. While 5-oxo-triazole piperidine-4-carboxamide moieties have a critical role in the inhibition of AChE and GST enzymes, hydroxy benzyl moiety is important for BChE enzyme inhibition.

Heteroleptic Metal Complexes of a Pyrimidinyl Based Schiff Base Ligand Incorporating 2,2'-Bipyridine Moiety: Synthesis, Characterization, and Biological Studies

A sequence of transition metal complexes of Mn(II), Co(II), Ni(II), and Cu(II) incorporating a novel pyrimidinyl based Schiff base ligand, 2-(4,6-dimethylpyrimidin-2-ylamino)naphthalene-1,4-dione (HL) and 2,2′-bipyridine has been synthesized and characterized using elemental, magnetic, conductance, infrared (FT-IR), nuclear magnetic resonance (¹H- and ¹³C-NMR), electronic (UV-Vis), electrospray ionization mass spectrometry (ESI-MS), thermographic analysis (TGA), and molecular docking studies. The acquired results were consistent with the adoption of the chemical formula, [M(X)(L)(Y)]·nH₂O (where M = Mn, Co, Ni, and Cu; L = Schiff base; X = 2,2′-bipy; Y = OAc; and n = 0,1) for the metallic complexes. HL ligand acts as a bidentate chelator and coordinates to metallic ion centre through carbonyl oxygen atom and deprotonated imide nitrogen. Similarly, 2,2′-bipy acts as a non-ionic bidentate chelator coordinating to metallic ion center via two nitrogen atoms. The mixed ligand complexes were appraised against pathogenic strains: S. aureus, P. aeruginosa, E. coli, B. cereus, P. mirabilis, K. oxytoca, A. niger, A. flevus, and R. Stolonifer. The antimicrobial studies gave moderate-good activity. Molecular docking studies on these compounds were done to indicate binding interactions between the compounds and adopted drug targets. Additionally, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity of the compounds were determined at different concentrations. The antioxidant study showed good radical scavenging abilities.