Novel ciprofloxacin and norfloxacin-tetrazole hybrids as potential antibacterial and antiviral agents: targeting S. aureus topoisomerase and SARS-CoV-2-MPro

Recent Updates on Antibacterial Quinolones: Green Synthesis, Mode of Interaction and Structure-Activity Relationship

Quinolone antibiotics are a crucial class of synthetic antibacterial agents, widely utilized due to their broad spectrum of antibacterial activity. Due to the development of antimicrobial resistance, the potency of quinolone drugs decreased. Many conventional methods have been developed to elevate amination rate and to improve yield. These methods are generally characterized by prolonged reaction durations, high boiling solvents, harsh conditions, costly reagents and excessive heat generation, which have adversely affected the therapeutic efficacy of these compounds. Recently, green chemistry has focused on sustainable chemistry-dependent quinolone analogue synthesis methods that significantly reduce bacterial infections. These methods include one-pot synthesis, photoredox catalysis, phase transfer catalysis, ultrasonic irradiation, microwave-assisted, green solvent and catalyst-free synthesis, which often utilize energy-efficient, non-toxic and less time-consuming techniques, aligning with green chemistry principles to improve safety and environmental impact. Researchers continuously explore innovative approaches to applying these methods in synthetic reactions. This review includes a comprehensive analysis of synthetic literature from the past 15 years from Scopus, PubMed, Embase and WOS using keywords, such as green chemistry, quinolone and antibacterial, highlighting significant advancements and emerging trends. This work's importance lies in its extensive literature overview on green synthesis methods for quinolones and related heterocyclic compounds. Furthermore, to provide useful information for the generation of future antibacterial drugs, some structural-activity relationship studies and in silico studies have also been included to investigate the stable binding interactions between quinolone leads and various target proteins.

Structure-Activity Relationship of Ciprofloxacin towards S-Spike Protein of SARS-CoV-2: Synthesis and In-Silico Evaluation

The recent outbreak of the coronavirus (COVID-19) pandemic, caused by the SARS-CoV-2 virus, has posed serious threats to global health systems. Although several directions have been put by the WHO for effective treatment, use of antibiotics, particularly ciprofloxacin, in suspected and acquired Covid-19 patients has raised an even more serious concern of antibiotic resistance. Ciprofloxacin has been reported to inhibit entry of SARS-CoV-2 into the host cells via interacting with the spike (S) protein. However, a proper structure-activity relationship study of ciprofloxacin with the S-protein is lacking, which inhibits researchers from developing a more potent fluoroquinolone analogue, specific for inhibition of SARS-CoV-2 viral entry. Herein, in order to have a structure-activity relationship study, we have accomplished a short and convergent synthesis of different derivatives of ciprofloxacin and a detailed in-silico study using molecular docking to explore the interactions of the derivatives with S-protein. The ADMET studies also indicated the drug likeliness and nontoxicity of the derivatives. Furthermore, the molecular dynamics simulation approach was used to study the dynamical behavior after the best docked derivative binds to the protein, and the MM-PBSA approach was adopted to calculate the binding energies. This has led to a derivative that has higher interactions with the S-protein compared to ciprofloxacin, without hampering the dynamics of the interactions. The strong affinity of compound 5 with the SARS-CoV-2 spike RBD protein was further evaluated experimentally using biolayer interferometry (BLI). Furthermore, molecular docking and molecular dynamics simulation were extended to evaluate its binding with the mutated variants Delta and Omicron. We anticipate that the current study could lead to an alternative therapeutic viral inhibitor with a better efficacy than ciprofloxacin.

Fluoroquinolones tackling antimicrobial resistance: Rational design, mechanistic insights and comparative analysis of norfloxacin vs ciprofloxacin derivatives

Antimicrobial resistance poses a global health concern and develops a need to discover novel antimicrobial agents or targets to tackle this problem. Fluoroquinolone (FN), a DNA gyrase and topoisomerase IV inhibitor, has helped to conquer antimicrobial resistance as it provides flexibility to researchers to rationally modify its structure to increase potency and efficacy. This review provides insights into the rational modification of FNs, the causes of resistance to FNs, and the mechanism of action of FNs. Herein, we have explored the latest advancements in antimicrobial activities of FN analogues and the effect of various substitutions with a focus on utilizing the FN nucleus to search for novel potential antimicrobial candidates. Moreover, this review also provides a comparative analysis of two widely prescribed FNs that are ciprofloxacin and norfloxacin, explaining their rationale for their design, structure-activity relationships (SAR), causes of resistance, and mechanistic studies. These insights will prove advantageous for new researchers by aiding them in designing novel and effective FN-based compounds to combat antimicrobial resistance.

Repositioning of Antibiotics in the Treatment of Viral Infections

Drug repurposing, also known as drug repositioning, is a currently tested approach by which new uses are being assigned for already tested drugs. In this case there are antibiotics that are used to combat bacterial infections. However, antibiotics are among the drugs that have been studied for possible antiviral activities. Therefore, the aim of this work is to carry out a review of the studies of antibiotics that could be repositioned for the treatment of viral infections. Among the main antibiotics that have demonstrated antiviral activity are macrolides and glycopeptides. In addition, several antibiotics from the group of tetracyclines, fluoroquinolones, cephalosporins and aminoglycosides have also been studied for their antiviral activity. These antibiotics have demonstrated antiviral activity against both RNA and DNA viruses, including the recent pandemic virus SARS-CoV-2. Some of these antibiotics were selected in addition to its antiviral activity for their immunomodulatory and anti-inflammatory properties. Of the antibiotics that present antiviral activity, in many cases the mechanisms of action are not exactly known. The use of these antibiotics to combat viral infections remains controversial and is not generally accepted, since clinical trials are required to prove its effectiveness. Therefore, there is currently no antibiotic approved as antiviral therapy. Hence is necessary to present the studies carried out on antibiotics that can be repositioned in the future as antiviral drugs.

Theoretical biological activities and docking studies of new derivatives of acyclovir for the treatment of coronavirus disease 2019

Acyclovir is an established antiviral agent. The global emergence of the coronavirus disease 2019 (COVID-19) pandemic brought forth the necessity to investigate potential therapeutic attributes of existing drugs, including acyclovir, to combat this novel virus. The primary focus of this research was to assess the theoretical bioactivities of acyclovir derivatives and to evaluate their molecular docking capacities, thereby determining their prospective application in treating COVID-19. A set of 22 ligand molecules derived from acyclovir were carefully selected for this study. Using the one-click docking technique, these derivatives underwent molecular interactions with specific proteins sourced from the Protein Data Bank, identified by IDs 1R4L, 1S49, 1AJ6, and 1PVG. The molecular docking analysis revealed that acyclovir derivatives no. 3, 5, 8, and 14 displayed the highest docking scores and could be potential candidates as therapeutic agents against COVID-19 based on these scores. Further experimental validations are essential to establish their efficacy in clinical settings.

Recent Development of Fluoroquinolone Derivatives as Anticancer Agents

Cancer is the second leading cause of death in the world following cardiovascular disease. Its treatment, including radiation therapy and surgical removal of the tumour, is based on pharmacotherapy, which prompts a constant search for new and more effective drugs. There are high costs associated with designing, synthesising, and marketing new substances. Drug repositioning is an attractive solution. Fluoroquinolones make up a group of synthetic antibiotics with a broad spectrum of activity in bacterial diseases. Moreover, those compounds are of particular interest to researchers as a result of reports of their antiproliferative effects on the cells of the most lethal cancers. This article presents the current progress in the development of new fluoroquinolone derivatives with potential anticancer and cytotoxic activity, as well as structure-activity relationships, along with possible directions for further development.

Novel fluoroquinolones analogues bearing 4-(arylcarbamoyl)benzyl: design, synthesis, and antibacterial evaluation

Bacterial resistance to fluoroquinolone has been increasing at an alarming rate worldwide. In an attempt to find more potent anti-bacterial agents, an efficient, straightforward protocol was performed to obtain a large substrate scope of novel ciprofloxacin and sarafloxacin analogues conjugated with 4-(arylcarbamoyl)benzyl 7a-ab. All prepared compounds were evaluated for their anti-bacterial activities against three gram-positive strains (Methicillin resistant staphylococcus aureus (MRSA), Staphylococcus aureus, and Enterococcus faecalis) as well as three gram-negative strains (Pseudomonas aeruginosa, Klebsiella pneumonia, and Escherichia coli) through three standard methods including broth microdilution, agar-disc diffusion, and agar-well diffusion assays. Most of the compounds exhibited great to excellent anti-bacterial potencies against MRSA and S. aureus. Among the targeted compounds, derivative 7n exhibited great antibacterial potency, which was noticeably more potent than parent ciprofloxacin. Subsequently, a molecular docking study was performed for this compound to find out its probable binding mode with the active site of S. aureus DNA gyrase (PDB ID: 2XCT).

Advancements in Synthetic Strategies and Biological Effects of Ciprofloxacin Derivatives: A Review

Ciprofloxacin is a widely used antibiotic in the fluoroquinolone class. It is widely acknowledged by various researchers worldwide, and it has been documented to have a broad range of other pharmacological activities, such as anticancer, antiviral, antimalarial activities, etc. Researchers have been exploring the synthesis of ciprofloxacin derivatives with enhanced biological activities or tailored capability to target specific pathogens. The various biological activities of some of the most potent and promising ciprofloxacin derivatives, as well as the synthetic strategies used to develop them, are thoroughly reviewed in this paper. Modification of ciprofloxacin via 4-oxo-3-carboxylic acid resulted in derivatives with reduced efficacy against bacterial strains. Hybrid molecules containing ciprofloxacin scaffolds displayed promising biological effects. The current review paper provides reported findings on the development of novel ciprofloxacin-based molecules with enhanced potency and intended therapeutic activities which will be of great interest to medicinal chemists.

Synthesis of tetrazole hybridized with thiazole, thiophene or thiadiazole derivatives, molecular modelling and antimicrobial activity

BACKGROUND

Tetrazole-based derivatives and their electronic structures have displayed interesting antimicrobial activity.

METHODS

The tetrazole-based hybrids linked with thiazole, thiophene and thiadiazole ring systems have been synthesized through various chemical reactions. The computational method DFT/B3LYP has been utilized to calculate their electronic properties. The antimicrobial effectiveness was investigated against representative bacterial and fungal strains. Additionally, the synthesized derivatives binding interaction was stimulated by docking program against PDB ID: 4URO as a model of the ATP binding domain of S. aureus DNA Gyrase subunit B.

RESULTS

The structures of the synthesized tetrazole-based derivatives were confirmed by IR, NMR, and Mass spectroscopic data. The DFT/B3LYP method showed that the thiadiazole derivatives 9a-c had lower ΔEH-L than the thiophenes 7a-c and thiazoles 5a-c. The hybrids 5b, 5c, and 7b exhibited proper antibacterial activity against Gram's +ve bacterial strains (S. aureus and S. pneumonia), while 9a displayed potent activity towards Gram's -ve bacterial strains (S. typhimurium and E. coli). Meanwhile, derivatives 5a-b, 7a, 7c, and 9c showed good effectiveness towards fungal strain (C. albicans).

CONCLUSION

The study provides valuable tetrazole core-linked heterocyclic rings and opens the door to further research on their electrical characteristics and applications. Tetrazoles and thiazoles have antibacterial properties in pharmacological frameworks, making these hybrids potential lead molecules for drug development. The conclusion summarizes the data and suggests that the synthesized chemicals' interaction with a particular protein domain suggests focused biological activity.

Synthesis, analysis of mol-ecular and crystal structures, estimation of inter-molecular inter-actions and biological properties of 1-benzyl-6-fluoro-3-[5-(4-methylcyclohexyl)-1,2,4-oxadiazol-3-yl]-7-(piperidin-1-yl)quinolin-4-one

The title compound, C30H33N4O2F, can be obtained via a two-step synthetic scheme involving 1-benzyl-6-fluoro-4-oxo-7-(piperidin-1-yl)-1,4-di-hydro-quino-line-3-carbo-nitrile as a starting compound that undergoes substitution with hydroxyl-amine and subsequent cyclization with 4-methyl-cyclo-hexane-1-carb-oxy-lic acid. It crystallizes from 2-propanol in the triclinic space group P with a mol-ecule of the title compound and one of 2-propanol in the asymmetric unit. After the mol-ecular structure was clarified using NMR and LC/MS, the mol-ecular and crystalline arrangements were defined with SC-XRD. A Hirshfeld surface analysis was performed for a better understanding of the inter-molecular inter-actions. One strong (O-H⋯O) and three weak [C-H⋯F (intra-molecular) and two C-H⋯O] hydrogen bonds were found. The contributions of short contacts to the Hirshfeld surface were estimated using two-dimensional fingerprint plots showing that O⋯H/H⋯O, C⋯H/H⋯C and C⋯C contacts are the most significant for the title compound and O⋯H for the 2-propanol. The crystal structure appears to have isotropically packed tetra-mers containing two mol-ecules of the title compound and two mol-ecules of 2-propanol as the building unit according to analysis of the distribution of pairwise inter-action energies. A mol-ecular docking study was carried out to evaluate the inter-actions of the title compound with the active centers of macromolecules corresponding to viral targets, namely, anti-hepatitis B activity [HBV, capsid Y132A mutant (VCID 8772) PDB ID: 5E0I] and anti-COVID-19 main protease activity (PDB ID: 6LU7). The data obtained revealed a noticeable affinity towards them that exceeded that of the reference ligands.