Pyridine N-oxide derivatives are inhibitory to the human SARS and feline infectious peritonitis coronavirus in cell culture

Assessing in vitro stability of remdesivir (GS-5734) and conversion to GS-441524 in feline plasma and whole blood

Feline infectious peritonitis (FIP) is a potentially fatal coronavirus-driven disease of cats. Treatment with nucleoside analogue GS-441524 and or prodrug remdesivir (RDV) have produced remission in both experimentally induced and naturally occurring FIP, yet information regarding metabolism of RDV into GS-441524 in cats is scarce. This study assessed possible phase I metabolism of RDV in cats, utilising an in vitro feline microsome model with in vitro t1/2 and in vitro Clint calculated using the substrate depletion method. A previously validated high-performance liquid chromatography (HPLC) fluorescence method was utilised for detection and analysis of RDV and GS-441524. Qualitative yield of RDV and intermediate metabolite GS-441524 were determined following microsome incubation, then compared to whole blood and plasma incubations. In vitro microsome incubation resulted in rapid depletion of RDV, though it did not appear to resemble a conventional phase I-dependent reaction in cats, as it is in humans and dogs. Depletion of RDV into GS-441524 was demonstrated in whole blood in vitro, suggesting cats convert RDV to GS-441524, likely via blood esterases, as observed in mice and rats. RDV metabolism is unlikely to be impacted by impaired liver function in cats. Furthermore, as RDV depletes within minutes, whereas GS-441524 is very stable, whole blood or plasma GS-441524 concentrations, rather than plasma RDV concentrations, are more appropriate for therapeutic drug monitoring (TDM) in cats receiving RDV.

Synthesis, Molecular Docking, and Dynamic Simulation Targeting Main Protease (Mpro) of New, Thiazole Clubbed Pyridine Scaffolds as Potential COVID-19 Inhibitors

Many biological activities of pyridine and thiazole derivatives have been reported, including antiviral activity and, more recently, as COVID-19 inhibitors. Thus, in this paper, we designed, synthesized, and characterized a novel series of N-aminothiazole-hydrazineethyl-pyridines, beginning with a N'-(1-(pyridine-3-yl)ethylidene)hydrazinecarbothiohydrazide derivative and various hydrazonoyl chlorides and phenacyl bromides. Their Schiff bases were prepared from the condensation of N-aminothiazole derivatives with 4-methoxybenzaldehyde. FTIR, MS, NMR, and elemental studies were used to identify new products. The binding energy for non-bonding interactions between the ligand (studied compounds) and receptor was determined using molecular docking against the SARS-CoV-2 main protease (PDB code: 6LU7). Finally, the best docked pose with highest binding energy (8a = -8.6 kcal/mol) was selected for further molecular dynamics (MD) simulation studies to verify the outcomes and comprehend the thermodynamic properties of the binding. Through additional in vitro and in vivo research on the newly synthesized chemicals, it is envisaged that the achieved results will represent a significant advancement in the fight against COVID-19.

Ultrafast excited state dynamics of pyridine N-oxide derivative in solution; femtosecond fluorescence up-conversion and theoretical calculations

In this study we have investigated 2-ethylamino-4-nitro-6-methyl pyridine N-oxide (2E6M) molecule that belongs to important group of Proton Coupled Electron Transfer (PCET) compounds where both the charge transfer (CT) and proton transfer processes in excited states may proceed. In this case, this is possible due to the donors and acceptors of electrons and protons in this system, as well as due to the presence of intramolecular {N-H… O [2,566(3) Å}, hydrogen bond.Using stationary and time-resolved spectroscopy, as well as quantum chemical calculations on the DFT and TD DFT B3LYP/6-31G (d,p) level of theory, a partial CT nature of the S₀ → S₁ transition in both tautomeric forms (N and T) has been revealed. Additionally, the excited state intramolecular proton transfer (ESIPT) process shown to be more favorable in apolar and weakly polar solvents than in strongly polar acetonitrile (E_N(S1) > E_T(S1). The displacement of charge from the amine group and the ring to the nitro group has been observed on the changing shapes of the HOMO and LUMO orbitals involved in this transition what further quantitatively allowed to realize the increase in the dipole moment of both forms in the electronic excited state. The calculations show that in two solvents with radically different polarity (heptane, acetonitrile), dipole moments of both forms are very similar [in acetonitrile u_N(S₁) and u_T(S₁) are 11.0 D and 11.5 D, respectively]. Hence, in polar media both forms can be stabilized in a comparable manner. This made it difficult for us to assign a single fluorescent band in acetonitrile to one of the tautomeric forms. However, it seems that due to application of time-resolved spectroscopy, this problem has been clarified. The TCSPC decay curve in acetonitrile with an ultrafast lifetime assigned to the (N) form, along with the femtosecond up-conversion signals that demonstrated only an ultrafast decay without any rise-time of a new excited (T) species, allowed us to conclude that in 2E6M in strongly polar solvent the ESIPT does not occur.The unique fluorescence band origins from the (N) form. In protic solvents, the significant kinetic isotopic effects have provided us with conclusive evidence for the presence of the solvent-assisted ESIPT process. Furthermore, it was noticed that the fluorescence lifetime in D₂O (100-120 fs) estimated from the up-conversion signals is about 40 times shorter relative to methanol. This may suggest that the sine qua non for the ESIPT process in 2E6M in protic solvents is the formation of a complex with a solvent molecule in the hydrogen bridge between the proton donor and proton acceptor, respectively.

Synthesis, spectroscopic, topological, hirshfeld surface analysis, and anti-covid-19 molecular docking investigation of isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate

Isopropyl 1-benzoyl-4-(benzoyloxy)-2,6-diphenyl-1,2,5,6-tetrahydropyridine-3-carboxylate (IDPC) was synthesized and characterized via spectroscopic (FT-IR and NMR) techniques. Hirshfeld surface and topological analyses were conducted to study structural and molecular properties. The energy gap (E_g), frontier orbital energies (E_HOMO, E_LUMO) and reactivity parameters (like chemical hardness and global hardness) were calculated using density functional theory with B3LYP/6–311++G (d,p) level of theory. Molecular docking of IDPC at the active sites of SARS-COVID receptors was investigated. IDPC molecule crystallized in the centrosymmetric triclinic (P1¯) space group. The topological and Hirshfeld surface analysis revealed that covalent, non-covalent and intermolecular H-bonding interactions, and electron delocalization exist in the molecular framework. Higher binding score (-6.966 kcal/mol) of IDPC at the active site of SARS-COVID main protease compared to other proteases suggests that IDPC has the potential of blocking polyprotein maturation. H-bonding and π-cationic and interactions of the phenyl ring and carbonyl oxygen of the ligand indicate the effective inhibiting potential of the compound against the virus.

Pyridine Compounds with Antimicrobial and Antiviral Activities

In the context of the new life-threatening COVID-19 pandemic caused by the SARS-CoV-2 virus, finding new antiviral and antimicrobial compounds is a priority in current research. Pyridine is a privileged nucleus among heterocycles; its compounds have been noted for their therapeutic properties, such as antimicrobial, antiviral, antitumor, analgesic, anticonvulsant, anti-inflammatory, antioxidant, anti-Alzheimer’s, anti-ulcer or antidiabetic. It is known that a pyridine compound, which also contains a heterocycle, has improved therapeutic properties. The singular presence of the pyridine nucleus, or its one together with one or more heterocycles, as well as a simple hydrocarbon linker, or grafted with organic groups, gives the key molecule a certain geometry, which determines an interaction with a specific protein, and defines the antimicrobial and antiviral selectivity for the target molecule. Moreover, an important role of pyridine in medicinal chemistry is to improve water solubility due to its poor basicity. In this article, we aim to review the methods of synthesis of pyridine compounds, their antimicrobial and antiviral activities, the correlation of pharmaceutical properties with various groups present in molecules as well as the binding mode from Molecular Docking Studies.

A Therapeutic Journey of Pyridine-Based Heterocyclic Compounds as Potent Anticancer Agents: A Review (From 2017 to 2021)

Pyridine derivatives are the most common and significant heterocyclic compounds, which show their fundamental characteristics to various pharmaceutical agents and natural products. Pyridine derivatives possess several pharmacological properties and a broad degree of structural diversity that is considered most valuable to explore the novel therapeutic agents. These compounds have an extensive range of biological activities such as antifungal, antibacterial, anticancer, anti-obesity, anti-inflammatory, antitubercular, antihypertensive, antineuropathic, antihistaminic, antiviral activities, and antiparasitic. The potent therapeutic properties of pyridine derivatives allow medicinal chemists to synthesize novel and effective chemotherapeutic agents. Consequently, the imperative objective of this comprehensive review is to summarize and investigate the literature regarding recent advancements in pyridine-based heterocycles to treat several kinds of cancer. Furthermore, the performances of pyridine derivatives were compared with some standard drugs including etoposide, sorafenib, cisplatin, and triclosan against different cancer cell lines. We hope this study will support the new thoughts to pursue the most active and less toxic rational designs.

Investigation of interactions between COVID-19 and diabetes with hereditary traits using real data: A case study in Turkey

In the present paper, interactions between COVID-19 and diabetes are investigated using real data from Turkey. Firstly, a fractional order pandemic model is developed both to examine the spread of COVID-19 and its relationship with diabetes. In the model, diabetes with and without complications are adopted by considering their relationship with the quarantine strategy. Then, the existence and uniqueness of solution are examined by using the fixed point theory. The dynamic behaviors of the equilibria and their stability analysis are studied. What is more, with the help of least-squares curve fitting technique (LSCFT), the fitting of the parameters is implemented to predict the direction of COVID-19 by using more accurately generated parameters. By trying to minimize the mean absolute relative error between the plotted curve for the infected class solution and the actual data of COVID-19, the optimal values of the parameters used in numerical simulations are acquired successfully. In addition, the numerical solution of the mentioned model is achieved through the Adams-Bashforth-Moulton predictor-corrector method. Meanwhile, the sensitivity analysis of the parameters according to the reproduction number is given. Moreover, numerical simulations of the model are obtained and the biological interpretations explaining the effects of model parameters are performed. Finally, in order to point out the advantages of the fractional order modeling, the memory trace and hereditary traits are taken into consideration. By doing so, the effect of the different fractional order derivatives on the COVID-19 pandemic and diabetes are investigated.

Sublimation Enthalpies of Substituted Pyridine N-Oxides

The enthalpies of sublimation of five substituted pyridine N-oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH₃→NO₂→OCH₃. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH₃-4-NO₂PyO and 3-CH₃-4-NO₂PyO. The relationship between the packing of molecules in crystals and the ΔH°_subl values is considered.

Synthesis and Characterization of Pyridine-Grafted Copolymers of Acrylic Acid-Styrene Derivatives for Antimicrobial and Fluorescence Applications

The goal of the present study was to copolymerize 3-(4-acetylphenylcarbamoyl) acrylic acid and styrene using azo-bis-isobutyronitrile (AIBN) as a catalyst. The resulting copolymers exhibited number average molecular weights (Mn) of 3.73-5.23 × 104 g/mol with a variable polydispersity (PDI = 2.3-3.8). The amide group of the PMA/PSA polymer was used for grafting poly (-styrene-maleic acid substituted aromatic 2-aminopyridine) by the Hantzsch reaction using a substituted aromatic aldehyde, malononitrile, and ammonium acetate. The polymer can emit strong blue fluorescence (λ = 510 nm) and its thermal stability and solubility were enhanced by polymer grafting. Moreover, the polymer showed the fluorescence spectra of the copolymer had a strong, broad emission band between 300 to 550 nm (maximum wavelength 538 nm) under excitation at 293 nm. The Hantzsch reaction yields an interesting class of nitrogen-based heterocycles that combine with a synthetic strategy for synthesis of grafted co-polymer pyridine-styrene derivatives. The as-prepared pyridine-based polymer compounds were screened against Gram-positive and Gram-negative bacteria, where a maximum inhibition zone toward all four types of bacteria was observed, including specific antifungal activity. Herein, a series of pyridine compounds were synthesized that showed enhanced fluorescent properties and antimicrobial properties due to their unique structure and ability to form polymer assemblies.

Drawing Comparisons between SARS-CoV-2 and the Animal Coronaviruses

The COVID-19 pandemic, caused by a novel zoonotic coronavirus (CoV), SARS-CoV-2, has infected 46,182 million people, resulting in 1,197,026 deaths (as of 1 November 2020), with devastating and far-reaching impacts on economies and societies worldwide. The complex origin, extended human-to-human transmission, pathogenesis, host immune responses, and various clinical presentations of SARS-CoV-2 have presented serious challenges in understanding and combating the pandemic situation. Human CoVs gained attention only after the SARS-CoV outbreak of 2002-2003. On the other hand, animal CoVs have been studied extensively for many decades, providing a plethora of important information on their genetic diversity, transmission, tissue tropism and pathology, host immunity, and therapeutic and prophylactic strategies, some of which have striking resemblance to those seen with SARS-CoV-2. Moreover, the evolution of human CoVs, including SARS-CoV-2, is intermingled with those of animal CoVs. In this comprehensive review, attempts have been made to compare the current knowledge on evolution, transmission, pathogenesis, immunopathology, therapeutics, and prophylaxis of SARS-CoV-2 with those of various animal CoVs. Information on animal CoVs might enhance our understanding of SARS-CoV-2, and accordingly, benefit the development of effective control and prevention strategies against COVID-19.

Role of heterocyclic compounds in SARS and SARS CoV-2 pandemic

Coronaviruses have led to severe emergencies in the world since the outbreak of SARS CoV in 2002, followed by MERS CoV in 2012. SARS CoV-2, the novel pandemic caused by coronaviruses that began in December 2019 in China has led to a total of 24,066,076 confirmed cases and a death toll of 823,572 as reported by World Health Organisation on 26 August 2020, spreading to 213 countries and territories. However, there are still no vaccines or medications available till date against SARS coronaviruses which is an urgent requirement to control the current pandemic like situations. Since many decades, heterocyclic scaffolds have been explored exhaustively for their anticancer, antimalarial, anti-inflammatory, antitubercular, antimicrobial, antidiabetic, antiviral and many more treatment capabilities. Therefore, through this review, we have tried to emphasize on the anticipated role of heterocyclic scaffolds in the design and discovery of the much-awaited anti-SARS CoV-2 therapy, by exploring the research articles depicting different heterocyclic moieties as targeting SARS, MERS and SARS CoV-2 coronaviruses. The heterocyclic motifs mentioned in the review can serve as crucial resources for the development of SARS coronaviruses treatment strategies.

Potential roles of medicinal plants for the treatment of viral diseases focusing on COVID-19: A review

The whole world is entangled by the coronavirus disease (COVID‐19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2), people are dying in thousands each day, and without an actual medication, it seems not possible for the bringing this global health crisis to a stop. Natural products have been in constant use since ancient times and are proven by time to be effective. Crude extract or pure compounds isolated from medicinal plants and/or herbs such as Artemisia annua, Agastache rugosa, Astragalus membranaceus, Cassia alata, Ecklonia cava, Gymnema sylvestre, Glycyrrhizae uralensis, Houttuynia cordata, Lindera aggregata, Lycoris radiata, Mollugo cerviana, Polygonum multiflorum, Pyrrosia lingua, Saposhnikoviae divaricate, Tinospora cordifolia etc. have shown promising inhibitory effect against coronavirus. Several molecules, including acacetin, amentoflavone, allicin, blancoxanthone, curcumin, daidzein, diosmin, epigallocatechin‐gallate, emodin, hesperidin, herbacetin, hirsutenone, iguesterin, jubanine G, kaempferol, lycorine, pectolinarin, phloroeckol, silvestrol, tanshinone I, taxifolin, rhoifolin, xanthoangelol E, zingerol etc. isolated from plants could also be potential drug candidates against COVID‐19. Moreover, these could also show promising inhibitory effects against influenza‐parainfluenza viruses, respiratory syncytial virus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome coronavirus (MERS‐CoV). Here, we have reported 93 antiviral drug candidates which could be a potential area of research in drug discovery.

Molecular structure and electron distribution of 4-nitropyridine N-oxide: Experimental and theoretical study of substituent effects

The molecular structure of 4-nitropyridine N-oxide, 4-NO₂-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH₃-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing –NO₂ group in para-position of 4-NO₂-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length r(N→O) in comparison to the non-substituted PyO. The presence of the electron-donating –CH₃ group in 4-CH₃-PyO leads to opposite structural changes. Electron density distribution in pyridine-N-oxide and its two substituted compounds are discussed in terms of natural bond orbitals (NBO) and quantum theory atoms in molecule (QTAIM).

I2-Promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones: facile and efficient synthesis of 1,4-dihydropyridazines and pyridazines

A facile and efficient strategy for the synthesis of 1,4-dihydropyridazines and pyridazines through I2-promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones has been developed. The switch in selectivity is attributed to the judicious choice of different reaction temperatures. The key features of this work include controllable and selective synthesis, good functional group tolerance, good to excellent reaction yields, metal/base-free conditions, and also applicability to one-pot methodology.

In silico and in vitro analysis of small molecules and natural compounds targeting the 3CL protease of feline infectious peritonitis virus

The computational search of chemical libraries has been used as a powerful tool for the rapid discovery of candidate compounds. To find small molecules with anti-feline infectious peritonitis virus (FIPV) properties, we utilized a virtual screening technique to identify the active site on the viral protease for the binding of the available natural compounds. The protease 3CL (3CL^pro) plays an important role in the replication cycle of FIPV and other viruses within the family Coronaviridae. The 15 best-ranked candidate consensus compounds, based on three docking tools, were evaluated for further assays. The protease inhibitor assay on recombinant FIPV 3CL^pro was performed to screen the inhibitory effect of the candidate compounds with IC₅₀ ranging from 6.36 ± 2.15 to 78.40 ± 2.60 μM. As determined by the cell-based assay, the compounds NSC345647, NSC87511, and NSC343256 showed better EC₅₀ values than the broad-spectrum antiviral drug ribavirin and the protease inhibitor lopinavir, under all the test conditions including pre-viral entry, post-viral entry, and prophylactic activity. The NSC87511 particularly yielded the best selective index (>4; range of SI = 13.80-22.90). These results indicated that the natural small-molecular compounds specifically targeted the 3CL^pro of FIPV and inhibited its replication. Structural modification of these compounds may generate a higher anti-viral potency for the further development of a novel therapy against FIP.

Crystal structure, vibrational and optic properties of 2-N-methylamino-3-methylpyridine N-oxide - Its X-ray and spectroscopic studies as well as DFT quantum chemical calculations

The crystal and molecular structure and physicochemical properties of 2-N-methylamino-3-methylpyridine N-oxide (MA3MPO) have been studied. MA3MPO was synthesized from 2-amino-3-methylpyridine by several steps to form colorless crystals suitable for crystallographic analysis. The data reveal that MA3MPO crystallizes in the monoclinic space group P2₁/n. The studied compound contains a nearly flat triply substituted pyridine skeleton whose structure is stabilized by an intramolecular N–H⋅⋅⋅O hydrogen bond. The N-oxide molecules are connected together by weak C–H⋯O hydrogen bonds, an acceptor of which is the oxygen atom from the N-oxide group. This leads to creation of two-dimensional network of hydrogen bonds. Its IR, Raman, UV–Vis and luminescence spectra have been measured and analyzed on the basis of DFT and NBO quantum chemical calculations in which the B3LYP/6-311++G(d,p) approach was applied. The distribution of the electron levels in the studied compound has been analyzed in terms of the possibility of its participation in the ligand-to-lanthanide ion energy transfer.

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The 2-N-methylamino-3-methylpyridine N-oxide (MA3MPO) was synthesized and characterized.

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The studied compound structure is stabilized by an intramolecular N–H⋯O hydrogen bond.

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The molecules are connected together by weak C–H⋯O hydrogen bonds.

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The amino group plays the role of effective hydrogen-bond donor but the N-oxide group is a hydrogen-bond acceptor.

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X-ray, IR, Raman and DFT methods recognized the existence of the intramolecular N–H⋯O hydrogen bond in the studied compound.

Copper-Catalyzed Aerobic 6-Endo-Trig Cyclization of β,γ-Unsaturated Hydrazones for the Divergent Synthesis of Dihydropyridazines and Pyridazines

A divergent synthetic strategy to 1,6-dihydropyridazines and pyridazines through Cu(II)-catalyzed controllable aerobic 6-endo-trig cyclization was developed. The selectivity can be rationally tuned via the judicious choice of reaction solvent. It was found that the 1,6-dihydropyridazines were obtained in moderate to high yields with CH₃CN as the reaction solvent, whereas employment of AcOH directly afforded pyridazines in up to 92% yields, probably arising from the oxidation of the in situ generated 1,6-dihydropyridazines.

Complexation of thorium with pyridine monocarboxylate-N-oxides: Thermodynamic and computational studies

The feed wastes and waste water treatment plants are the major sources for the entry of N-oxides into the soils then to aquatic life. The complexation of actinides with potentially stable anthropogenic ligands facilitate the transportation and migration of the actinides from the source confinement. The present study describes the determination of thermodynamic parameters for the complexation of Th(IV) with the three isomeric pyridine monocarboxylates (PCNO) namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO). The potentiometric and isothermal calorimetric titrations were carried out to determine the stability and enthalpy of the formations for all the Th(IV)-PCNO complexes. Th-PANO complexes are more stable than Th-NANO and Th-IANO complexes which can be attributed to chelate formation in the former complexes. Formation of all the Th-PCNO complexes are endothermic and are entropy driven. The geometries for all the predicted complexes are optimized the energies, bond distances and charges on individual atoms are obtained using TURBOMOLE software. The theoretical calculation corroborated the experimental determinations.

The molecular structure of 4-methylpyridine-N-oxide: Gas-phase electron diffraction and quantum chemical calculations

The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in C_S molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp² hybridization concept of the nitrogen and carbon atoms in the ring. The experimental geometric parameters are in a good agreement with the parameters for non-substituted N-oxide and reproduced very closely by DFT calculations. The presence of the electron-donating CH₃ substituent in 4-MePyO leads to a decrease of the ipso-angle and to an increase of r(N→O) in comparison with the non-substituted PyO. Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme. The nature of the semipolar N→O bond is discussed.

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The molecular structure of 4-methylpiridine-N-oxide has been studied by GED and quantum chemical calculations.

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Electron density distribution analysis has been performed in terms of natural bond orbitals (NBO) scheme.

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The molecule possesses C_S symmetry with the planar pyridine ring.

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Obtained molecular parameters confirm the hyperconjugation in the pyridine ring.

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The presence of the electron-donating CH₃ substituent in 4-MePyO results in an increase of r(N→O).

Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes

The mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAA) by oxo(salen)Cr(V)⁺ ion in the presence of ligand oxides has been studied spectrophotometrically in acetonitrile medium. Addition of ligand oxides (LO) causes a red shift in the λ _max values of oxo(salen) complexes and an increase in absorbance with the concentration of LO along with a clear isobestic point. The reaction shows first-order dependence on oxo(salen)-chromium(V)⁺ ion and fractional-order dependence on PSAA and ligand oxide. Michaelis-Menten kinetics without kinetic saturation was observed for the reaction. The order of reactivity among the ligand oxides is picoline N-oxide > pyridine N-oxide > triphenylphosphine oxide. The low catalytic activity of TPPO was rationalized. Both electron-withdrawing and electron-donating substituents in the phenyl ring of PSAA facilitate the reaction rate. The Hammett plots are non-linear upward type with negative ρ value for electron-donating substituents, (ρ ^- = -0.740 to -4.10) and positive ρ value for electron-withdrawing substituents (ρ ⁺ = +0.057 to +0.886). Non-linear Hammett plot is explained by two possible mechanistic scenarios, electrophilic and nucleophilic attack of oxo(salen)chromium(V)⁺-LO adduct on PSAA as the substituent in PSAA is changed from electron-donating to electron-withdrawing. The linearity in the log k vs. E _ox plot confirms single-electron transfer (SET) mechanism for PSAAs with electron-donating substituents.

Identification of the peptide derived from S1 domain that inhibits type I and type II feline infectious peritonitis virus infection

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Feline infectious peritonitis (FIP) is a coronavirus-induced fatal disease in cats.

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We synthesized peptides derived from the S1 domain of the type I FIPV S protein.

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We investigated inhibitory effects of peptides on FIPV infection.

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5 peptides significantly inhibited type I FIPV.

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2 of 5 peptides significantly inhibited not only type I, but also type II FIPV.

Feline infectious peritonitis virus (FIPV) can cause a lethal disease in cats, feline infectious peritonitis (FIP). A therapeutic drug that is effective against FIP has not yet been developed. Peptides based on viral protein amino acid sequences have recently been attracting attention as new antiviral drugs. In the present study, we synthesized 30 overlapping peptides based on the amino acid sequence of the S1 domain of the type I FIPV strain KU-2 S protein, and investigated their inhibitory effects on FIPV infection. To evaluate the inhibitory effects on type I FIPV infection of these peptides, we investigated a method to increase the infection efficiency of poorly replicative type I FIPV. The efficiency of type I FIPV infection was increased by diluting the virus with medium containing a polycation. Of the 30 peptides, I-S1-8 (S461-S480), I-S1-9 (S471-S490), I-S1-10 (S481-S500), I-S1-16 (S541-S560), and I-S1-22 (S601-S620) significantly decreased the infectivity of FIPV strain KU-2 while I-S1-9 and I-S1-16 exhibited marked inhibitory effects on FIPV infection. The inhibitory effects on FIPV infection of these 2 peptides on other type I and type II FIPV strains, feline herpesvirus (FHV), and feline calicivirus (FCV) were also examined. These 2 peptides specifically inhibited type I and type II FIPV, but did FHV or FCV infection. In conclusion, the possibility of peptides derived from the S protein of type I FIPV strain KU-2 as anti-FIPV agents effective not only for type I, but also type II FIPV was demonstrated in vitro.

Studies on polymorph conversion in a new cyclodextrin inclusion compound

4-Phenylpyridine-N-oxide and βCD form a stoichiometric inclusion complex with two polymorphs occurring at different crystallisation times. The irreversible conversion of one polymorph into the other was monitored in real time for the first time.

Peptides corresponding to the predicted heptad repeat 2 domain of the feline coronavirus spike protein are potent inhibitors of viral infection

Background

Feline infectious peritonitis (FIP) is a lethal immune-mediated disease caused by feline coronavirus (FCoV). Currently, no therapy with proven efficacy is available. In searching for agents that may prove clinically effective against FCoV infection, five analogous overlapping peptides were designed and synthesized based on the putative heptad repeat 2 (HR2) sequence of the spike protein of FCoV, and the antiviral efficacy was evaluated.

Methods

Plaque reduction assay and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cytotoxicity assay were performed in this study. Peptides were selected using a plaque reduction assay to inhibit Feline coronavirus infection.

Results

The results demonstrated that peptide (FP5) at concentrations below 20 μM inhibited viral replication by up to 97%. The peptide (FP5) exhibiting the most effective antiviral effect was further combined with a known anti-viral agent, human interferon-α (IFN-α), and a significant synergistic antiviral effect was observed.

Conclusion

Our data suggest that the synthetic peptide FP5 could serve as a valuable addition to the current FIP prevention methods.

Generation, characterization and therapeutic potential of anti-feline TNF-alpha MAbs for feline infectious peritonitis

Feline infectious peritonitis (FIP) is a lethal infectious disease affecting domestic and wild cats. Several reports suggested that TNF-alpha is related to the progression of FIP. Thus, the administration of a feline TNF-alpha-neutralizing antibody to cats with FIP may reduce the disease progression. In this study, we have prepared nine monoclonal antibodies (MAbs) that recognize feline TNF-alpha. All MAbs neutralized recombinant TNF-alpha. The 50% inhibitory concentrations (IC50) of the MAbs for the cytotoxicity of recombinant TNF-alpha were 5-684 ng/ml. MAb 2-4 exhibited high neutralizing activity against natural TNF-alpha derived from FIPV-infected macrophages, and was confirmed to inhibit the following feline TNF-alpha-induced conditions in vitro: (i) an increase in the survival rate of neutrophils from cats with FIP, (ii) aminopeptidase N (APN) mRNA expression in macrophages, and (iii) apoptosis of a feline T-lymphocyte cell line.

Effect of chloroquine on feline infectious peritonitis virus infection in vitro and in vivo

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Feline infectious peritonitis (FIP) is a coronavirus-induced fatal disease in cats.

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Chloroquine (CQ) has antiviral and anti-inflammatory effect in primary monocyte.

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Therapeutic effect of CQ for cats with experimentally induced FIP was evaluated.

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Clinical score of chloroquine-treated cats was better than untreated cats.

Feline infectious peritonitis (FIP) is a feline coronavirus-induced fatal disease in domestic and wild cats. Several studies have investigated potential treatments for FIP. However, there have been no reports on agents that have exhibited a therapeutic effect. Recently, chloroquine has been reported to antiviral effect. We investigated whether chloroquine can be used to treat FIP in vitro and in vivo. It was demonstrated that chloroquine has inhibitory effect against the replication of FIPV and anti-inflammatory effect in vitro. In vivo study using cats with experimentally induced FIP, the clinical score of chloroquine-treatment groups were better than in chloroquine-untreated group. However, alanine aminotransferase levels increased in the chloroquine-treated groups. It will be necessary to further investigate the possibility of FIP treatment with a combination of chloroquine and other agents.

A theoretical investigation of the structure of 2-nitropyridine-N-oxide and the dependency of the NO2 torsional motion on the applied wavefunction and basis set

HF, B3LYP, and MP2 wave functions in combination with Pople 6-31, 6-311 augmented with polarization functions on all atoms and Dunning double- and triple-zeta basis sets have been employed to investigate the structures and torsional potential function of the nitro group in 2-nitropyridine-N-oxide (2-NPO) and a variety of its fluorinated derivatives. The augmentation of the basis sets with diffuse functions showed a marked effect on the profile and barriers of the NO2 torsional potential. Depending on the applied model chemistry, the heterocyclic ring in some 2-NPOs has proved to be non-planar. The non-planarity of the ring was characterized by Cremer-Pople puckering amplitude Q. The disruption of the ring planarity in some NPOs was accounted for the distinctive reactivity and impact sensitivity of these heterocycles. Consistently, the NBO and the AIM analyses furnished clear evidence for the accentuated weakness of the C-NO2 bond and provided evidence for the electronic interplay between the NO2 group, the fluorine substituent and the heterocyclic ring. Deletion of all off-diagonal Fock-matrix elements (NOSTAR) to separate hyperconjugative stabilizing interactions from steric interactions was used. The effect of nitration and fluorination on the aromaticity of the studied 2-NPOs was investigated by using the NICS descriptors NICS(1) and NICS(1)zz. These NICS indices have shown that the fluorination in para position to the nitro group exhibits the highest degree of aromaticity within the fluorinated 2-NPOs.

Oxidation reactions using polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine

A thermally stable polymer-supported oxidant has been developed. Polymer-supported 2-benzenesulfonyl-3-(4-nitrophenyl)oxaziridine was applied to microwave-assisted reactions that occurred at high temperatures and was shown to oxidize alkenes, silyl enol ethers, and pyridines to the corresponding epoxides and pyridine N-oxides in excellent to good yields and with much shorter reaction times. It also enabled tetrahydrobenzimidazoles to be oxidatively rearranged to spiro fused 5-imidazolones in a more efficient manner. Recycling of the polymer-supported oxidant is also possible with minimal loss of activity after several reoxidations.

Medicinal herbal extracts of Sophorae radix, Acanthopanacis cortex, Sanguisorbae radix and Torilis fructus inhibit coronavirus replication in vitro

BACKGROUND

Cimicifuga rhizome, Meliae cortex, Coptidis rhizome and Phellodendron cortex have been previously shown to exhibit anti-coronavirus activity. Here, an additional 19 traditional medicinal herbal extracts were evaluated for antiviral activities in vitro.

METHODS

A plaque assay was used to evaluate the effects of 19 extracts, and the concentration of extract required to inhibit 50% of the replication (EC(50)) of mouse hepatitis virus (MHV) A59 strain (MHV-A59) was determined. The 50% cytotoxic concentration (CC(50)) of each extract was also determined. Northern and western blot analyses were conducted to evaluate antiviral activity on viral entry, viral RNA and protein expression, and release in MHV-infected DBT cells.

RESULTS

Sophorae radix, Acanthopanacis cortex and Torilis fructus reduced intracellular viral RNA levels with comparable reductions in viral proteins and MHV-A59 production. The extracts also reduced the replication of the John Howard Mueller strain of MHV, porcine epidemic diarrhoea virus and vesicular stomatitis virus in vitro. Sanguisorbae radix reduced coronavirus production, partly as a result of decreased protein synthesis, but without a significant reduction in intracellular viral RNA levels. The EC(50) values of the four extracts ranged from 0.8 to 3.7 microg/ml, whereas the CC(50) values ranged from 156.5 to 556.8 microg/ml. Acanthopanacis cortex and Torilis fructus might exert their antiviral activities in MHV-A59-infected cells by inducing cyclooxygenase-2 expression via the activation of extracellular signal-related kinase (ERK) and p38 or ERK alone, respectively.

CONCLUSIONS

Sophorae radix, Acanthopanacis cortex, Sanguisorbae radix and Torilis fructus might be considered as promising novel anti-coronavirus drug candidates.

Inhibition of RNA Helicases of ssRNA(+) Virus Belonging to Flaviviridae, Coronaviridae and Picornaviridae Families

Many viral pathogens encode the motor proteins named RNA helicases which display various functions in genome replication. General strategies to design specific and selective drugs targeting helicase for the treatment of viral infections could act via one or more of the following mechanisms: inhibition of the NTPase activity, by interferences with ATP binding and therefore by limiting the energy required for the unwinding and translocation, or by allosteric mechanism and therefore by stabilizing the conformation of the enzyme in low helicase activity state; inhibition of nucleic acids binding to the helicase; inhibition of coupling of ATP hydrolysis to unwinding; inhibition of unwinding by sterically blocking helicase translocation. Recently, by in vitro screening studies, it has been reported that several benzotriazole, imidazole, imidazodiazepine, phenothiazine, quinoline, anthracycline, triphenylmethane, tropolone, pyrrole, acridone, small peptide, and Bananin derivatives are endowed with helicase inhibition of pathogen viruses belonging to Flaviviridae, Coronaviridae, and Picornaviridae families.

Aromatic N-oxide bridged copper(II) coordination polymers: Synthesis, characterization and magnetic properties

The complexes [Cu2(o-NO2-C6H4COO)4(PNO)2] (1), [Cu2(C6H5COO)4(2,2'-BPNO)] n (2), [Cu2(C6H5COO)4(4,4'-BPNO)] n (3), [Cu(p-OH-C6H4COO)2(4,4'-BPNO)2·H2O] n (4), (where PNO = pyridine N-oxide, 2,2'-BPNO = 2,2'-bipyridyl-N,N'-dioxide, 4,4'-BPNO = 4,4'-bipyridyl-N,N'-dioxide) are prepared and characterized and their magnetic properties are studied as a function of temperature. Complex 1 is a discrete dinuclear complex while complexes 2-4 are polymeric of which 2 and 3 have paddle wheel repeating units. Magnetic susceptibility measurements from polycrystalline samples of 1-4 revealed strong antiferromagnetic interactions within the {Cu2}4+ paddle wheel units and no discernible interactions between the units. The complex 5, [Cu(NicoNO)2·2H2O] n ·4nH2O, in which the bridging ligand to the adjacent copper(II) ions is nicotinate N-oxide (NicoNO) the transmitted interaction is very weakly antiferromagnetic.

Shuffling multivariate adaptive regression splines and adaptive neuro-fuzzy inference system as tools for QSAR study of SARS inhibitors

In this work, the inhibitory activity of pyridine N-oxide derivatives against human severe acute respiratory syndrome (SARS) is predicted in terms of quantitative structure–activity relationship (QSAR) models. These models were developed with the aid of multivariate adaptive regression spline (MARS) and adaptive neuro-fuzzy inference system (ANFIS) combined with shuffling cross-validation technique. A shuffling MARS algorithm is utilized to select the most important variables in QSAR modeling and then these variables were used as inputs of ANFIS to predict SARS inhibitory activities of pyridine N-oxide derivatives. A data set of 119 drug-like compounds was coded with over hundred calculated meaningful molecular descriptors. The best descriptors describing the inhibition mechanism were solvation connectivity index, length to breadth ratio, relative negative charge, harmonic oscillator of aromatic index, average molecular weight and total path count. These parameters are among topological, electronic, geometric, constitutional and aromaticity descriptors. The statistical parameters of R² and root mean square error (RMSE) are 0.884 and 0.359, respectively. The accuracy and robustness of shuffling MARS–ANFIS model in predicting inhibition behavior of pyridine N-oxide derivatives (pIC₅₀) was illustrated using leave-one-out and leave-multiple-out cross-validation techniques and also by Y-randomization. Comparison of the results of the proposed model with those of GA-PLS-ANFIS shows that the shuffling MARS–ANFIS model is superior and can be considered as a tool for predicting the inhibitory behavior of SARS drug-like molecules.