Favipiravir tautomerism: a theoretical insight

Investigation of substituent effects on the electronic structure and antiviral activity of favipiravir derivatives for Covid-19 treatment using DFT and molecular docking

In this study, Density-functional theory/Time-dependent density-functional theory (DFT/TDDFT) and Molecular docking method was used to investigate the effect of methyl acetate, tetrahydrofuran and cyanobenzylidene substituents on the electronic structure and antiviral activity of favipiravir for treating COVID-19. The DFT and TDDFT computations were employed using the Gaussian 09 software package. The values were calculated using the 6-311++G(d, p) basis set and the hybrid B3LYP functional method. Autodock vina software was used for simulations to better predictions and to validate the modified compounds' binding affinities and poses. Results of the study indicate that compounds 1 to 6 all displayed a planar structure, where the pyrazine ring, carboxamide, hydroxyl groups, and other substituents are all situated within the same plane. In addition, the energy gaps (Egap) of these six compounds (Cpd 1, 2, 3, 4, 5, and 6) were compared. The significant dipole moment and binding affinity achieved implies a particular orientation for binding within the target protein, signaling the anticipated strength of the binding interaction. In all six compounds, the electrophilic domain is situated in the vicinity of the amine functional group within the carboxamide compound, whereas the nucleophilic domain encompasses both the carbonyl and hydroxyl groups. The most negatively charged sites are susceptible to electrophilic interactions. In conclusion, compounds 5 and 6 exhibit a high binding affinity of the target protein, while compound 6 has a high energy gap, which could enhance its antiviral activity against the COVID-19 virus.

Structural flexibility of favipiravir and its structural analogues in solutions: experimental and computational insight

Combined UV-vis and quantum chemical studies of the structural flexibility and tautomerism of 6-R-3-hydroxy-2-pyrazine carboxamides in solutions revealed that their keto-enol transformations are accompanied by the deprotonation of enol tautomers and the formation of the corresponding anionic species. Both the solvent and the 6-R substituent strongly influence the relative abundance of the above forms in solutions. Anions are not formed in 1,2-dichloroethane (DCE), but the probability of deprotonation in neutral water and N,N-dimethylformamide (DMF) increases in the order R = H < F < NO2. Only enol tautomers of all solutes are found in DCE. DMF stabilizes keto forms only moderately and assists much strongly in the deprotonation of all three compounds. Water tends to stabilize both keto tautomers and deprotonated anions: the keto form dominates in the case of R = H (antiviral drug T-1105), the anions are found exclusively for R = NO2, and the aqueous solution of another antiviral drug, favipiravir (R = F), contains both the keto tautomer and the anionic form. The results of quantum chemical free energy calculations are in agreement with the experimental observations.

Detection of sub-nmol amounts of the antiviral drug favipiravir in 19F MRI using photo-chemically induced dynamic nuclear polarization

In biological tissues, 19F magnetic resonance (MR) enables the non-invasive, background-free detection of 19F-containing biomarkers. However, the signal-to-noise ratio (SNR) is usually low because biomarkers are typically present at low concentrations. Measurements at low magnetic fields further reduce the SNR. In a proof-of-principal study we applied LED-based photo-chemically induced dynamic nuclear polarization (photo-CIDNP) to amplify the 19F signal at 0.6 T. For the first time, 19F MR imaging (MRI) and spectroscopy (MRS) of a fully biocompatible model system containing the antiviral drug favipiravir has been successfully performed. This fluorinated drug has been used to treat Ebola and COVID-19. Since the partially cyclic reaction scheme for photo-CIDNP allows for multiple data acquisitions, averaging further improved the SNR. The mean signal gain factor for 19F has been estimated to be in the order of 103. An in-plane resolution of 0.39 × 0.39 mm2 enabled the analysis of spatially varying degrees of hyperpolarization. The minimal detectable amount of favipiravir per voxel was estimated to about 500 pmol. The results show that 19F photo-CIDNP is a promising method for the non-invasive detection of suitable 19F-containing drugs and other compounds with very low levels of the substance.

Molecular modeling of the structural, electronic, excited state dynamic, and the photovoltaic properties of the oligomers of n-corannulene (n = 1-4)

Despite the fact that n-corannulene oligomers (n = 1-4) have a variety of electronic and optical properties, including the ability to be tuned and the potential to be used as light-harvesting materials, there has not been a computational assessment of their structural, electronic, and optical properties. Herein, a computational evaluation of the concerned materials regarding their potent use in solar cell technology has been conducted via DFT/CAM-B3LYP and M062X/6-311+G level of theory. It was observed that the calculated 1st frequency of the n-Corannulene (n = 1-4) were 144.15, 106.36, 48.96 and 42.21 respectively. Notably, the computed cohesive energy value increased as the number of Corannulene units increases while the electronic characteristics revealed that the chemical activity of the structures increased as the number of oligomers rose. Both calculation techniques demonstrate that the number of n-Corannulene oligomers increases the HOMO energy while decreasing the LUMO energy based on the external electric field (EF) effect. The findings demonstrated that as EF intensity increases, the energy gap (Eg/eV = |EHOMO-ELUMO|) of these molecular systems decreases which can be attributed to a decrease in the electron transfer potential barrier. The 4-Corannulene systems showed the highest wave length of adsorption for the investigated compound at 546.18 nm, with the highest oscillator strength of 0.2708 and the lowest transition energy of 2.2700 eV, arising from S0-S1 (H-L) and the highest major percentage contribution of 93.34 % in comparison to the investigated compounds. We are hopeful that this research will help experimental researchers understand the potential of n-Corannulene, specifically 4-corannulene, as powerful material for a variety of applications ranging from solar cell, photovoltaic properties and many others.

A highly sensitive and green electroanalytical method for the determination of favipiravir in pharmaceutical and biological fluids

BACKGROUND

Favipiravir is currently used for the treatment of coronavirus disease-2019 (COVID-19).

OBJECTIVE

A highly sensitive and eco-friendly electroanalytical method was developed to quantify favipiravir.

METHOD

The voltammetric method optimized a sensor composed of reduced graphene oxide / modified carbon paste electrode in the presence of an anionic surfactant, improving the favipiravir detection limit. The investigation reveals that favipiravir-oxidation is a diffusion-controlled irreversible process. The effects of various pH and scan rates on oxidation anodic peak current were investigated.

RESULTS

The developed method offers a wide linear dynamic range of 1.5-420 ng/mL alongside a higher sensitivity with a limit of detection in the nanogram range (0.44 ng/mL) and a limit of quantification in the low nanogram range (1.34 ng/mL).

CONCLUSION

The proposed method was applied for the determination of favipiravir in the dosage form, human plasma and urine samples. The developed method exhibited good selectivity in the presence of two potential electroactive biological interferants, uric acid which increases during favipiravir therapy and the recommended co-administered vitamin C. The organic solvent-free method greenness was evaluated via the Green Analytical Procedure Index, The present work offers a simple, sensitive and environment-friendly method fulfilling green chemistry concepts.

Tautomerism and Rotamerism of Favipiravir and Halogenated Analogues in Solution and in the Solid State

Favipiravir is an important selective antiviral against RNA-based viruses, and currently, it is being repurposed as a potential drug for the treatment of COVID-19. This type of chemical system presents different carboxamide-rotameric and hydroxyl-tautomeric states, which could be essential for interpreting its selective antiviral activity. Herein, the tautomeric 3-hydroxypyrazine/3-pyrazinone pair of favipiravir and its 6-substituted analogues, 6-Cl, 6-Br, 6-I, and 6-H, were fully investigated in solution and in the solid state through ultraviolet-visible, 1H nuclear magnetic resonance, infrared spectroscopy, and X-ray diffraction techniques. Also, a study of the gas phase was performed using density functional theory calculations. In general, the keto-enol balance in these 3-hydroxy-2-pyrazinecarboxamides is finely modulated by external and internal electrical variations via changes in solvent polarity or by replacement of substituents at position 6. The enol tautomer was prevalent in an apolar environment, whereas an increase in the level of the keto tautomer was favored by an increase in solvent polarity and, even moreso, with a strong hydrogen-donor solvent. Keto tautomerization was favored either in solution or in the solid state with a decrease in 6-substituent electronegativity as follows: H ≫ I ≈ Br > Cl ≥ F. Specific rotameric states based on carboxamide, "cisoide" and "transoide", were identified for the enol and keto tautomer, respectively; their rotamerism is dependent on the tautomerism and not the aggregation state.

A dispersion-corrected DFT calculation on encapsulation of favipiravir drug used as antiviral against COVID-19 into carbon-, boron-, and aluminum-nitride nanotubes for optimal drug delivery systems combined with molecular docking simulations

Favipiravir (FAV) (6-fluoro-3-oxo-3,4-dihydropyrazine-2-carboxamide) is one of the most effective antiviral drugs which is cited for action against RNA-viral infections of COVID-19. In this study, density functional theory (DFT) calculations were used to investigate three nanotubes (NTs) with FAV drug as delivery systems. The encapsulated systems (ESs) consist of FAV drug inside carbon-carbon, aluminum nitride, and boron nitride. At B3LYP-D/6-31G(d,p) and CPCM/B3LYP-D/6-31G(d,p), the optimization of NTs, FAV, and its tautomeric forms and six ESs was investigated in gas and water environments. Five tautomeric forms of FAV were investigated, two keto forms (K1 and K2) and three enol forms (E1, E2, and E3). The results revealed that E3 and K2 isomeric forms represented the most stable structures in both media; thus, these two forms were encapsulated into the NTs. The stability and the synthesis feasibility of NTs have been proven by calculating their interaction energies. Non-covalent interactions (NCIs) were investigated in the ESs to show the type of NCI with the molecular voids. The binding energies, thermochemical parameters, and recovery times were investigated to understand the mechanism of FAV encapsulation and release. The encapsulated AlNNT systems are more favorable than those of BNNTs and CNTs in gas and aqueous environments with much higher binding energies. The quantum theory of atoms in molecules (QTAIM) and recovery time analysis revealed the easier releasing of E3 from AlNNT over K2 form. Based on molecular docking simulations, we found that E3 and K2 FAV forms showed a high level of resistance to SARS-CoV-6M3M/6LU7/6W9C proteases.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11224-023-02182-4.

Evaluation of In Vitro Distribution and Plasma Protein Binding of Selected Antiviral Drugs (Favipiravir, Molnupiravir and Imatinib) against SARS-CoV-2

There are a number of uncertainties regarding plasma protein binding and blood distribution of the active drugs favipiravir (FAVI), molnupiravir (MOLNU) and imatinib (IMA), which were recently proposed as therapeutics for the treatment of COVID-19 disease. Therefore, proton dissociation processes, solubility, lipophilicity, and serum protein binding of these three substances were investigated in detail. The drugs display various degrees of lipophilicity at gastric (pH 2.0) and blood pH (pH 7.4). The determined pK_a values explain well the changes in lipophilic character of the respective compounds. The serum protein binding was studied by membrane ultrafiltration, frontal analysis capillary electrophoresis, steady-state fluorometry, and fluorescence anisotropy techniques. The studies revealed that the ester bond in MOLNU is hydrolyzed by protein constituents of blood serum. Molnupiravir and its hydrolyzed form do not bind considerably to blood proteins. Likewise, FAVI does not bind to human serum albumin (HSA) and α1-acid glycoprotein (AGP) and shows relatively weak binding to the protein fraction of whole blood serum. Imatinib binds to AGP with high affinity (logK' = 5.8-6.0), while its binding to HSA is much weaker (logK' ≤ 4.0). The computed constants were used to model the distribution of IMA in blood plasma under physiological and 'acute-phase' conditions as well.

Importance of tautomerism in drugs

Tautomerism is an important phenomenon exhibited by many drugs. As we discuss in this review, identifying the different tautomers of drugs and exploring their importance in the mechanisms of drug action are integral components of current drug discovery. Nuclear magnetic resonance (NMR), infrared (IR), ultraviolet (UV), Raman, and terahertz spectroscopic techniques, as well as X-ray diffraction, are useful for exploring drug tautomerism. Quantum chemical methods, in association with pharmacoinformatics tools, are being used to evaluate tautomeric preferences in terms of energy effects. Desmotropy (i.e., tautomeric polymorphism) of the drugs is particularly important in drug delivery studies.

Favipiravir-Tautomeric and Complexation Properties in Solution

The tautomeric properties of favipiravir were investigated experimentally for the first time by using molecular spectroscopy (UV-Vis absorption, fluorescence and NMR), as well as DFT quantum-chemical calculations. According to the obtained results, the enol tautomer is substantially more stable in most of the organic solvents. In the presence of water, a keto form appears to be favored due to the specific solute-solvent interactions. Upon the addition of alkaline-earth-metal ions, deprotonation and complexation occurred simultaneously, giving the formation of 2 : 1 ligand : metal complexes. According to the theoretical simulations, the metal ion is captured between the carbonyl groups as a result of the size-fit effect.

Favipiravir in SARS-CoV-2 Infection: Is it Worth it?

Favipiravir is a potential antiviral drug undergoing clinical trials to manage various viral infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Favipiravir possesses antiviral properties against RNA viruses, including SARS-CoV-2. Unfortunately, these viruses do not have authorized antiviral drugs for the management of diseases resulting from their infection, hence the dire need to accentuate the discovery of antiviral drugs that are efficacious and have a broad spectrum. Favipiravir acts primarily by blocking inward and outward movements of the virus from cells. Favipiravir is a prodrug undergoing intracellular phosphorylation and ribosylation to form an active form, favipiravir-RTP, which binds viral RNA-dependent RNA polymerase (RdRp). Considering the novel mechanism of favipiravir action, especially in managing viral infections, it is vital to pay more attention to the promised favipiravir hold in the management of SARS-CoV-2, its efficacy, and dosage regimen, and interactions with other drugs. In conclusion, favipiravir possesses antiviral properties against RNA viruses, including COVID- 19. Favipiravir is effective against SARS-CoV-2 infection through inhibition of RdRp. Pre-clinical and large-scalp prospective studies are recommended for efficacy and long-term safety of favipiravir in COVID-19.

Inhibition of Viral RNA-Dependent RNA Polymerases by Nucleoside Inhibitors: An Illustration of the Unity and Diversity of Mechanisms

RNA-dependent RNA polymerase (RdRP) is essential for the replication and expression of RNA viral genomes. This class of viruses comprise a large number of highly pathogenic agents that infect essentially all species of plants and animals including humans. Infections often lead to epidemics and pandemics that have remained largely out of control due to the lack of specific and reliable preventive and therapeutic regimens. This unmet medical need has led to the exploration of new antiviral targets, of which RdRP is a major one, due to the fact of its obligatory need in virus growth. Recent studies have demonstrated the ability of several synthetic nucleoside analogs to serve as mimics of the corresponding natural nucleosides. These mimics cause stalling/termination of RdRP, or misincorporation, preventing virus replication or promoting large-scale lethal mutations. Several such analogs have received clinical approval and are being routinely used in therapy. In parallel, the molecular structural basis of their inhibitory interactions with RdRP is being elucidated, revealing both traditional and novel mechanisms including a delayed chain termination effect. This review offers a molecular commentary on these mechanisms along with their clinical implications based on analyses of recent results, which should facilitate the rational design of structure-based antiviral drugs.

Exploring the permeability of covid-19 drugs within the cellular membrane: a molecular dynamics simulation study

The diffusion of drugs into the cellular membrane is an important step in the drug delivery systems. Furthermore, predicting the interaction and permeability of drugs across the cellular membrane could help scientists to design bioavailable and high-efficient drugs. Discovering the COVID-19 drugs has recently drawn remarkable attention to tackle its outbreak. Due to the rapid replication of the coronavirus in the human body, searching for highly permeable drugs into the cellular membrane is vital. Herein, we performed the molecular dynamics (MD) simulation and density functional (DFT) calculations to investigate the permeability of keto and enol tautomers of the favipiravir (FAV) as well as hydroxychloroquine (HCQ) COVID-19 drugs into the cellular membrane. Our results reveal that though both keto and enol tautomers of the FAV are feasible to transfer through the cellular membrane, the keto form moves faster and diffuses deeper; however, the HCQ molecules aggregate in the water phase and remain near the cellular membrane. It is worth pointing out that the obtained results are consistent with the reactivity trends projected by the calculated reactivity descriptors of the considered drugs. Despite the pair correlation function and H-bond analyses revealing the interactions between the membrane and HCQ, the aggregation of the HCQ molecules resists their passage through the cellular membrane. Besides, the lower free energy barrier of FAV confirms its higher permeability than HCQ. These findings suggest that due to the deeper permeability of the FAV drug, its effectiveness can be more than that of HCQ. These molecular insights might help with a better understanding of the interactions between COVID-19 drugs and cellular membranes. Moreover, these theoretical findings could help experimental researchers find high-efficient strategies for COVID-19 therapy.

Theoretical insights into the effect of halogenated substituent on the electronic structure and spectroscopic properties of the favipiravir tautomeric forms and its implications for the treatment of COVID-19

In this study, we systematically investigated the electronic structure, spectroscopic (nuclear magnetic resonance, infrared, Raman, electron ionization mass spectrometry, UV-Vis, circular dichroism, and emission) properties, and tautomerism of halogenated favipiravir compounds (fluorine, chlorine, and bromine) from a computational perspective. Additionally, the effects of hydration on the proton transfer mechanism of the tautomeric forms of the halogenated favipiravir compounds are discussed. Our results suggest that spectroscopic properties allow for the elucidation of such tautomeric forms. As is well-known, the favipiravir compound has excellent antiviral properties and hence was recently tested for the treatment of new coronavirus (SARS-CoV-2). Through in silico modeling, in the current study, we evaluate the role of such tautomeric forms in order to consider the effect of drug-metabolism in the inhibition process of the main protease (Mpro) and RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 virus. According to the molecular docking, all halogenated compounds presented a better interaction energy than the co-crystallized active ligand (-3.5 kcal mol-1) in the viral RdRp, in both wild-type (-6.3 to -6.5 kcal mol-1) and variant (-5.4 to -5.6 kcal mol-1) models. The variant analyzed for RdRp (Y176C) decreases the affinity of the keto form of the compounds in the active site, and prevented the ligands from interacting with RNA. These findings clearly indicated that all these compounds are promising as drug candidates for this molecular target.

Preliminary investigation of drug impurities associated with the anti-influenza drug Favipiravir - An insilico approach

The role of repurposed or modified antiviral drugs has become more significant during the current global pandemic of SARS Covid-19. In the present study, four structurally analogous impurity molecules of antiviral drug Favipiravir are selected for preliminary computational investigation for assessing the structure-activity relationship. The optimized geometry and the electronic structures of the compounds are computed using Density Functional Theory as a precursor to evaluating their physical, chemical and spectral properties. The frontier orbitals analysis is performed to obtain global reactivity parameters namely, the chemical potential, absolute electronegativity, global softness, global hardness, electrophilicity, etc. The natural Bond Orbital (NBO) analysis and Mulliken analysis provided an understanding of the charge-transfer interactions of molecules. The possibilities of intermolecular interactions of the drug systems with the receptors are also visualized using the electrostatic potential maps (MEP) derived from the DFT computations. The physiochemical properties are assessed computationally using SwissADME webtool to correlate the structural aspects of the compounds with their biological responses. Useful parameters namely flexibility, lipophilicity, size, polarity, solubility and saturation were also computed to evaluate the therapeutic activity or drug-likeness.

Electron attachment to isolated and microhydrated favipiravir

Electron attachment and its equivalent in complex environments, single-electron reduction, are important in many biological processes. Here, we experimentally study the electron attachment to favipiravir, a well-known antiviral agent. Electron attachment spectroscopy is used to explore the energetics of associative (AEA) and dissociative (DEA) electron attachment to isolated favipiravir. AEA dominates the interaction and the yields of the fragment anions after DEA are an order of magnitude lower than that of the parent anion. DEA primary proceeds via decomposition of the CONH2 functional group, which is supported by reaction threshold calculations using ab initio methods. Mass spectrometry of small favipiravir-water clusters demonstrates that a lot of energy is transferred to the solvent upon electron attachment. The energy gained upon electron attachment, and the high stability of the parent anion were previously suggested as important properties for the action of several electron-affinic radiosensitizers. If any of these mechanisms cause synergism in chemo-radiation therapy, favipiravir could be repurposed as a radiosensitizer.

Discovery of (E)-N-(4-cyanobenzylidene)- 6-fluoro- 3-hydroxypyrazine-2 -carboxamide (cyanorona-20): the first potent and specific anti-COVID-19 drug

Abstract

Specific inhibition of the viral RNA-dependent RNA polymerase (RdRp) of the newly-emerged severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a very promising strategy for developing highly potent medicines for coronavirus disease 2019 (COVID-19). However, almost all of the reported viral RdRp inhibitors (either repurposed drugs or new antiviral agents) lack selectivity against the SARS-CoV-2 RdRp. Herein, I discovered a new favipiravir derivative, (E)-N-(4-cyanobenzylidene)-6-fluoro-3-hydroxypyrazine-2-carboxamide (cyanorona-20), as the first potent SARS-CoV-2 inhibitor with very high selectivity (209- and 45-fold more potent than favipiravir and remdesivir, respectively). Based on the significant reduction in the in vitro SARS-CoV-2 replication/copies, strong computational cyanorona-20 ligand-RdRp protein interactions, and anti-RdRp activity of the parent favipiravir drug, SARS-CoV-2 inhibition is thought to be mediated through the coronaviral-2 RdRp inhibition. This promising selective anti-COVID-19 compound is also, to the best of our knowledge, the first bioactive derivative of favipiravir, the known antiinfluenza and antiviral drug. This new nucleoside analog was designed, synthesized, characterized, computationally studied (through pharmacokinetic calculations along with computational molecular modeling and prediction), and biologically evaluated for its anti-COVID-19 activities (through a validated in vitro anti-COVID-19 assay). The results of the biological assay showed that cyanorona-20 surprisingly exhibited very significant anti-COVID-19 activity (anti-SARS-CoV-2 EC₅₀ = 0.45 μM), and, in addition, it could be also a very promising lead compound for the design of new anti-COVID-19 agents. Cyanorona-20 is a new favipiravir derivative with promise for the treatment of SARS-CoV-2 infection.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s11696-021-01640-9.

First electrochemical evaluation of favipiravir used as an antiviral option in the treatment of COVID-19: A study of its enhanced voltammetric determination in cationic surfactant media using a boron-doped diamond electrode

Favipiravir, a promising antiviral agent, is undergoing clinical trials for the potential treatment of the novel coronavirus disease 2019 (COVID-19). This is the first report for the electrochemical activity of favipiravir and its electroanalytical sensing. For this purpose, the effect of cationic surfactant, CTAB was demonstrated on the enhanced accumulation of favipiravir at the surface of cathodically pretreated boron-doped diamond (CPT-BDD) electrode. At first, the electrochemical properties of favipiravir were investigated in the surfactant-free solutions by the means of cyclic voltammetry. The compound presented a single oxidation step which is irreversible and adsorption controlled. A systematic study of various operational conditions, such as electrode pretreatment, pH of the supporting electrolyte, concentration of CTAB, accumulation variables, and instrumental parameters on the adsorptive stripping response, was examined using square-wave voltammetry. An oxidation signal at around +1.21 V in Britton-Robinson buffer at pH 8.0 containing 6 × 10^-4 M CTAB allowed to the adsorptive stripping voltammetric determination of favipiravir (after 60 s accumulation step at open-circuit condition). The process could be used in the concentration range with two linear segments of 0.01-0.1 μg mL^-1 (6.4 × 10^-8-6.4 × 10^-7 M) and 0.1-20.0 μg mL^-1 (6.4 × 10^-7-1.3 × 10^-4 M). The limit of detection values were found to be 0.0028 μg mL^-1 (1.8 × 10^-8 M), and 0.023 μg mL^-1 (1.5 × 10^-7 M) for the first and second segments of calibration graph, respectively. The feasibility of developed methodology was tested to the analysis of the commercial tablet formulations and model human urine samples.

8-(Pyridin-2-yl)quinolin-7-ol as a Platform for Conjugated Proton Cranes: A DFT Structural Design

Theoretical design of conjugated proton cranes, based on 7-hydroxyquinoline as a tautomeric sub-unit, has been attempted by using ground and excited state density functional theory (DFT) calculations in various environments. The proton crane action request existence of a single enol tautomer in ground state, which under excitation goes to the excited keto tautomer through a series of consecutive excited-state intramolecular proton transfer (ESIPT) steps with the participation of the crane sub-unit. A series of substituted pyridines was used as crane sub-units and the corresponding donor-acceptor interactions were evaluated. The results suggest that the introduction of strong electron donor substituents in the pyridine ring creates optimal conditions for 8-(pyridin-2-yl)quinolin-7-ols to act as proton cranes.