Synthetic and medicinal perspective of quinolines as antiviral agents

Novel 7-Chloro-(4-thioalkylquinoline) Derivatives: Synthesis and Antiproliferative Activity through Inducing Apoptosis and DNA/RNA Damage

A series of 78 synthetic 7-chloro-(4-thioalkylquinoline) derivatives were investigated for cytotoxic activity against eight human cancer as well as 4 non-tumor cell lines. The results showed, with some exceptions, that sulfanyl 5-40 and sulfinyl 41-62 derivatives exhibited lower cytotoxicity for cancer cell lines than those of well-described sulfonyl N-oxide derivatives 63-82. As for compound 81, the most pronounced selectivity (compared against BJ and MRC-5 cells) was observed for human cancer cells from HCT116 (human colorectal cancer with wild-type p53) and HCT116p53-/- (human colorectal cancer with deleted p53), as well as leukemia cell lines (CCRF-CEM, CEM-DNR, K562, and K562-TAX), lung (A549), and osteosarcoma cells (U2OS). A good selectivity was also detected for compounds 73 and 74 for leukemic and colorectal (with and without p53 deletion) cancer cells (compared to MRC-5). At higher concentrations (5 × IC₅₀) against the CCRF-CEM cancer cell line, we observe the accumulation of the cells in the G0/G1 cell phase, inhibition of DNA and RNA synthesis, and induction of apoptosis. In addition, X-ray data for compound 15 is being reported. These results provide useful scientific data for the development of 4-thioalkylquinoline derivatives as a new class of anticancer candidates.

Identification of a novel immune-inflammatory signature of COVID-19 infections, and evaluation of pharmacokinetics and therapeutic potential of RXn-02, a novel small-molecule derivative of quinolone

Coronavirus disease 2019 (COVID-19) is a global pandemic and respiratory infection that has enormous damage to human lives and economies. It is caused by SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), a non-pair-stranded positive-sense RNA virus. With increasing global threats and few therapeutic options, the discovery of new potential drug targets and the development of new therapy candidates against COVID-19 are urgently needed. Based on these premises, we conducted an analysis of transcriptomic datasets from SARS-CoV-2-infected patients and identified several SARS-CoV-2 infection signatures, among which TNFRSF5/PTPRC/IDO1/MKI67 appeared to be the most pertinent signature. Subsequent integrated bioinformatics analysis identified the signature as an important immunomodulatory and inflammatory signature of SARS-CoV-2 infection. It was suggested that this gene signature mediates the interplay of immune and immunosuppressive cells leading to infiltration-exclusion of effector memory T cells in the lungs, which is of translation relevance for developing novel SARS-CoV-2 drug and vaccine candidates. Consequently, we designed and synthesized a novel small-molecule quinoline derivative (RXn-02) and evaluated its pharmacokinetics in rats, revealing a peak plasma concentration (Cmax) and time to Cmax (Tmax) of 1.756 μg/mL and 0.6 h, respectively. Values of the area under the curve (AUC) (0–24 h) and AUC (0 h∼∞) were 18.90 and 71.20 μg h/mL, respectively. Drug absorption from the various regional segments revealed that the duodenum (49.84%), jejunum (47.885%), cecum (1.82%), and ileum (0.32%) were prime sites of RXn-02 absorption. No absorption was detected from the stomach, and the least was from the colon (0.19%). Interestingly, RXn-02 exhibited in vitro antiproliferative activities against hub gene hyper-expressing cell lines; A549 (IC₅₀ = 48.1 μM), K-562 (IC₅₀ = 100 μM), and MCF7 (IC₅₀ = 0.047 μM) and against five cell lines originating from human lungs (IC₅₀ range of 33.2–69.5 μM). In addition, RXn-02 exhibited high binding efficacies for targeting the TNFRSF5/PTPRC/IDO1/MK signature with binding affinities (ΔG) of −6.6, −6.0, −9.9, −6.9 kcal/mol respectively. In conclusion, our study identified a novel signature of SARS-CoV-2 pathogenesis. RXn-02 is a drug-like candidate with good in vivo pharmacokinetics and hence possesses great translational relevance worthy of further preclinical and clinical investigations for treating SARS-CoV-2 infections.

Arylselenyl Radical-Mediated Cyclization of N-(2-Alkynyl)anilines: Access to 3-Selenylquinolines

An efficient and novel approach to accessing 3-selenylquinolines from diaryl diselenides and acyclic, selenium-free substrates is described. Preliminary mechanistic studies indicate that the combination of CuCl₂ and air affords an appropriate environment for producing arylselenyl radicals that initiate the cascade cyclization of N-(2-alkynyl)anilines, forming key Se-C and C-C bonds in a single step. Using this chemistry, a wide variety of 3-selenylquinolines were produced in moderate to excellent yield under mild conditions, highlighting the versatility and usefulness of this new method.

Synthesis and biological evaluation of new 2‑substituted‑4‑amino-quinolines and -quinazoline as potential antifungal agents

Aiming to discover novel antifungal agents, a series of 2‑substituted‑4‑amino-quinolines and -quinazoline were prepared and characterized using IR, ¹H NMR, ¹³C NMR, and HRMS spectroscopic techniques. Their antifungal activities against four invasive fungi were evaluated, and the results revealed that some of the target compounds exhibited moderate to excellent inhibitory potencies. The most promising compounds III₁₁, III₁₄, III_15, and III₂₃ exhibited potent and broad-spectrum antifungal activities with MIC values of 4-32 μg/mL. The mechanism studies showed that compound III₁₁ (N,2-di-p-tolylquinolin-4-amine hydrochloride) did not play antifungal potency by disrupting fungal membrane, which was quite different from many traditional membrane-active antifungal drugs. Meanwhile, III₁₁ also demonstrated a low likelihood of inducing resistance, and excellent stability in mouse plasma. In addition, some interesting structure-activity relationships (SARs) were also discussed. These results suggest that some 4‑aminoquinolines may serve as new and promising candidates for further antifungal drug discovery.

Discovery of 2-Phenylquinolines with Broad-Spectrum Anti-coronavirus Activity

A selection of compounds from a proprietary library, based on chemical diversity and various biological activities, was evaluated as potential inhibitors of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in a phenotypic-based screening assay. A compound based on a 2-phenylquinoline scaffold emerged as the most promising hit, with EC₅₀ and CC₅₀ values of 6 and 18 μM, respectively. The subsequent selection of additional analogues, along with the synthesis of ad hoc derivatives, led to compounds that maintained low μM activity as inhibitors of SARS-CoV-2 replication and lacked cytotoxicity at 100 μM. In addition, the most promising congeners also show pronounced antiviral activity against the human coronaviruses HCoV-229E and HCoV-OC43, with EC₅₀ values ranging from 0.2 to 9.4 μM. The presence of a 6,7-dimethoxytetrahydroisoquinoline group at the C-4 position of the 2-phenylquinoline core gave compound 6g that showed potent activity against SARS-CoV-2 helicase (nsp13), a highly conserved enzyme, highlighting a potentiality against emerging HCoVs outbreaks.

A Review on Medicinally Important Heterocyclic Compounds

Heterocyclic compounds account for the most prominent and diverse class of organic compounds. A significant number of heterocyclic compounds have been synthesized up to this point. Heterocyclic compounds are rapidly increasing in number due to extensive synthetic research and also their synthetic utility. Such compounds have a wide range of uses in the field of medicinal chemistry. Dyestuff, sanitizers, corrosion inhibitors, antioxidants, and copolymer synthesis are additional well-known applications. There are always distinguishing characteristics of an efficient approach for producing newly discovered heterocyclic compounds and their moieties. According to prior research, more than 90% of medicines containing heterocyclic compounds have been developed after the obtainment of a thorough scientific grasp of the biological system. It was discovered in the neoteric developments of heterocyclic compounds that these play a vital role in curative chemistry, and exert anticancer, anti-inflammatory, antifungal, antiallergic, antibacterial, anti-HIV, antiviral, anti-convulsant, and other biological activities. The present article provides detailed information regarding such heterocyclic compounds.

Uracil as a Zn-Binding Bioisostere of the Allergic Benzenesulfonamide in the Design of Quinoline-Uracil Hybrids as Anticancer Carbonic Anhydrase Inhibitors

A series of quinoline-uracil hybrids (10a-l) has been rationalized and synthesized. The inhibitory activity against hCA isoforms I, II, IX, and XII was explored. Compounds 10a-l demonstrated powerful inhibitory activity against all tested hCA isoforms. Compound 10h displayed the best selectivity profile with good activity. Compound 10d displayed the best activity profile with minimal selectivity. Compound 10l emerged as the best congener considering both activity (IC50 = 140 and 190 nM for hCA IX and hCA XII, respectively) and selectivity (S.I. = 13.20 and 9.75 for II/IX, and II/XII, respectively). The most active hybrids were assayed for antiproliferative and pro-apoptotic activities against MCF-7 and A549. In silico studies, molecular docking, physicochemical parameters, and ADMET analysis were performed to explain the acquired CA inhibitory action of all hybrids. A study of the structure-activity relationship revealed that bulky substituents at uracil N-1 were unfavored for activity while substituted quinoline and thiouracil were effective for selectivity.

The Potential of 2-Substituted Quinolines as Antileishmanial Drug Candidates

There is a need for new, cost-effective drugs to treat leishmaniasis. A strategy based on traditional medicine practiced in Bolivia led to the discovery of the 2-substituted quinoline series as a source of molecules with antileishmanial activity and low toxicity. This review documents the development of the series from the first isolated natural compounds through several hundred synthetized molecules to an optimized compound exhibiting an in vitro IC₅₀ value of 0.2 µM against Leishmania donovani, and a selectivity index value of 187, together with in vivo activity on the L. donovani/hamster model. Attempts to establish structure–activity relationships are described, as well as studies that have attempted to determine the mechanism of action. For the latter, it appears that molecules of this series act on multiple targets, possibly including the immune system, which could explain the observed lack of drug resistance after in vitro drug pressure. We also show how nanotechnology strategies could valorize these drugs through adapted formulations and how a mechanistic targeting approach could generate new compounds with increased activity.

Mono- and combinational drug therapies for global viral pandemic preparedness

Broadly effective antiviral therapies must be developed to be ready for clinical trials, which should begin soon after the emergence of new life-threatening viruses. Here, we pave the way towards this goal by reviewing conserved druggable virus-host interactions, mechanisms of action, immunomodulatory properties of available broad-spectrum antivirals (BSAs), routes of BSA delivery, and interactions of BSAs with other antivirals. Based on the review, we concluded that the range of indications of BSAs can be expanded, and new pan- and cross-viral mono- and combinational therapies can be developed. We have also developed a new scoring algorithm that can help identify the most promising few of the thousands of potential BSAs and BSA-containing drug cocktails (BCCs) to prioritize their development during the critical period between the identification of a new virus and the development of virus-specific vaccines, drugs, and therapeutic antibodies.

A Review of Modifications of Quinoline Antimalarials: Mefloquine and (hydroxy)Chloroquine

Late-stage modification of drug molecules is a fast method to introduce diversity into the already biologically active scaffold. A notable number of analogs of mefloquine, chloroquine, and hydroxychloroquine have been synthesized, starting from the readily available active pharmaceutical ingredient (API). In the current review, all the modifications sites and reactivity types are summarized and provide insight into the chemistry of these molecules. The approaches include the introduction of simple groups and functionalities. Coupling to other drugs, polymers, or carriers afforded hybrid compounds or conjugates with either easily hydrolyzable or more chemically inert bonds. The utility of some of the compounds was tested in antiprotozoal, antibacterial, and antiproliferative assays, as well as in enantiodifferentiation experiments.

Biology of quinoline and quinazoline alkaloids

Quinoline and quinazoline alkaloids, two important classes of N-based heterocyclic compounds, have attracted scientific and popular interest worldwide since the 19th century. More than 600 compounds have been isolated from nature to date. To build on our two prior reviews, we reexamined the promising molecules described in previous reports and provided updated literature on novel quinoline and quinazoline alkaloids isolated over the past 5 years. This chapter reviews and discusses 205 molecules with a broad range of bioactivities, including antiparasitic and insecticidal, antibacterial and antifungal, cardioprotective, antiviral, anti-inflammatory, and other effects. This survey should provide new clues or possibilities for the discovery of new and better drugs from the original naturally occurring quinoline and quinazoline alkaloids.

Novel Quinolone Derivatives: Synthesis and Antioxidant Activity

Novel quinolone derivatives have been designed and readily synthesized according to a simple protocol including O-alkylation and Claisen rearrangement processes. Structures of the synthesized compounds have been confirmed by IR, 1H and 13C NMR, and mass spectra. The new products have been tested for their antioxidant activity, and two of those demonstrate high antioxidant activity.

Recent contributions of quinolines to antimalarial and anticancer drug discovery research

Quinoline, a privileged scaffold in medicinal chemistry, has always been associated with a multitude of biological activities. Especially in antimalarial and anticancer research, quinoline played (and still plays) a central role, giving rise to the development of an array of quinoline-containing pharmaceuticals in these therapeutic areas. However, both diseases still affect millions of people every year, pointing to the necessity of new therapies. Quinolines have a long-standing history as antimalarial agents, but established quinoline-containing antimalarial drugs are now facing widespread resistance of the Plasmodium parasite. Nevertheless, as evidenced by a massive number of recent literature contributions, they are still of great value for future developments in this field. On the other hand, the number of currently approved anticancer drugs containing a quinoline scaffold are limited, but a strong increase and interest in quinoline compounds as potential anticancer agents can be seen in the last few years. In this review, a literature overview of recent contributions made by quinoline-containing compounds as potent antimalarial or anticancer agents is provided, covering publications between 2018 and 2020.

Synthesis of quinolines via sequential addition and I2-mediated desulfurative cyclization

An efficient one-pot approach for the synthesis of quinolines from o-aminothiophenol and 1,3-ynone under mild conditions is disclosed. With the aid of ESI-MS analysis and parallel experiments, a three-step mechanism is proposed-a two-step Michael addition-cyclization condensation step leading to intermediate 1,5-benzothiazepine catalyzed by zirconocene amino acid complex Cp2Zr(η1-C9H10NO2)2, followed by I2-mediated desulfurative step.

New heteroanalogs of tricyclic ascidian alkaloids: synthesis and biological activity

Heteroanalogs of ascidian alkaloids have been synthesized, and for the first time 10 different types of saturated carbo- and heteroannulated pyridones have been obtained. A new method for the formation of decahydro[1,3]oxazolo[2,3-j]quinoline and octahydro-5H-cyclopenta[b][1,3]oxazolo[3,2-a]pyridine was proposed. The synthesis of these heterocycles is based on the three-component cyclization of trifluoroacetoacetic ester and cycloketones with 1,2- and 1,3-dinucleophiles. It was found that reactions with amino alcohols are distinguished by the possibility of isolating carbocyclopyridones of various degrees of saturation. The diastereomeric structure of the synthesized heterocycles has been studied, and the mechanism of their formation has been proposed. Antitumor, anti-influenza and analgesic agents have been found among the synthesized compounds.

Hybrid Quinoline-Thiosemicarbazone Therapeutics as a New Treatment Opportunity for Alzheimer's Disease‒Synthesis, In Vitro Cholinesterase Inhibitory Potential and Computational Modeling Analysis

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the leading cause of dementia worldwide. The limited pharmacological approaches based on cholinesterase inhibitors only provide symptomatic relief to AD patients. Moreover, the adverse side effects such as nausea, vomiting, loss of appetite, muscle cramps, and headaches associated with these drugs and numerous clinical trial failures present substantial limitations on the use of medications and call for a detailed insight of disease heterogeneity and development of preventive and multifactorial therapeutic strategies on urgent basis. In this context, we herein report a series of quinoline-thiosemicarbazone hybrid therapeutics as selective and potent inhibitors of cholinesterases. A facile multistep synthetic approach was utilized to generate target structures bearing multiple sites for chemical modifications and establishing drug-receptor interactions. The structures of all the synthesized compounds were fully established using readily available spectroscopic techniques (FTIR, ¹H- and ¹³C-NMR). In vitro inhibitory results revealed compound 5b as a promising and lead inhibitor with an IC₅₀ value of 0.12 ± 0.02 μM, a 5-fold higher potency than standard drug (galantamine; IC₅₀ = 0.62 ± 0.01 μM). The synergistic effect of electron-rich (methoxy) group and ethylmorpholine moiety in quinoline-thiosemicarbazone conjugates contributes significantly in improving the inhibition level. Molecular docking analysis revealed various vital interactions of potent compounds with amino acid residues and reinforced the in vitro results. Kinetics experiments revealed the competitive mode of inhibition while ADME properties favored the translation of identified inhibitors into safe and promising drug candidates for pre-clinical testing. Collectively, inhibitory activity data and results from key physicochemical properties merit further research to ensure the design and development of safe and high-quality drug candidates for Alzheimer’s disease.

Pyridine Scaffolds, Phenols and Derivatives of Azo Moiety: Current Therapeutic Perspectives

Synthetic heterocyclic compounds have incredible potential against different diseases; pyridines, phenolic compounds and the derivatives of azo moiety have shown excellent antimicrobial, antiviral, antidiabetic, anti-melanogenic, anti-ulcer, anticancer, anti-mycobacterial, anti-inflammatory, DNA binding and chemosensing activities. In the present review, the above-mentioned activities of the nitrogen-containing heterocyclic compounds (pyridines), hydroxyl (phenols) and azo derivatives are discussed with reference to the minimum inhibitory concentration and structure–activity relationship, which clearly indicate that the presence of nitrogen in the phenyl ring; in addition, the hydroxyl substituent and the incorporation of a diazo group is crucial for the improved efficacies of the compounds in probing different diseases. The comparison was made with the reported drugs and new synthetic derivatives that showed recent therapeutic perspectives made in the last five years.

Chemodynamic therapy agents Cu(II) complexes of quinoline derivatives induced ER stress and mitochondria-mediated apoptosis in SK-OV-3 cells

Three Cu(II) complexes of quinoline derivatives as cancer chemodynamic therapy agents were synthesized and characterized. These complexes were heavily taken up by cells and reacted with cellular glutathione (GSH) to reduce Cu²⁺ to Fenton-like Cu⁺, which catalyzed endogenous H₂O₂ to produce the highly toxic hydroxyl radicals (•OH) to kill cancer cells. Cu1 and Cu2 initiated CAT activity declines, mitochondrial membrane potential and ATP concentration decrease, mitochondrial Ca²⁺ overload and ER stress response, leading to cell cycle arrest in sub-G1 and cancer cell caspase-dependent apoptosis. On account of the high GSH and H₂O₂ specific properties of the tumor microenvironment, Cu1 and Cu2 exhibited higher in vitro anticancer activity and lower toxicity to normal cells. Cu1 and Cu2 efficiently inhibited tumor growth in the SK-OV-3 xenograft mouse model without obvious systemic toxicity.

Direct functionalization of quinoxalin-2(1H)-one with alkanes: C(sp2)-H/C(sp3)-H cross coupling in transition metal-free mode

Considering the significance of pharmaceutically important heterocycles, efficient and highly versatile protocols for the functionalization of diverse heterocycles with easily accessible feedstock are crucial. Here, we have reported selective alkylation of quinoxalin-2(1H)-one with a broad class of hydrocarbons having different C(sp³)-H bonds with varying bond strengths using di-tert-butyl peroxide (DTBP) as an alkoxyl radical mediator for hydrogen atom transfer (HAT). This dehydrogenative coupling approach utilizes feedstock chemicals such as cycloalkanes, cyclic ethers and alkyl arenes as coupling partners. This protocol exhibits good functional group compatibility and selectivity regarding both heterocycles and unactivated alkanes. Moreover, this methodology allows functionalization of relatively strong C-H bonds of adamantane and exclusive selectivity towards 3° C(sp³)-H bonds is observed. We also illustrate the applicability of this C(sp²)-H/C(sp³)-H cross-coupling for practical access to bioactive pharmaceuticals.