Evaluation of chalcone derivatives for their role as antiparasitic and neuroprotectant in experimentally induced cerebral malaria mouse model.

Cerebral malaria is a severe complication of Plasmodium falciparum infection with a complex pathophysiology. The current course of treatment is ineffective in lowering mortality or post-treatment side effects such as neurological and cognitive abnormalities. Chalcones are enormously distributed in spices, fruits, vegetables, tea, and soy-based foodstuffs that are well known for their antimalarial activity, and in recent years they have been widely explored for brain diseases like Alzheimer's disease. Therefore, considering the previous background of chalcones serving as both antimalarial and neuroprotective, the present study aimed to study the effect of these chalcone derivatives on an experimental model of cerebral malaria (CM). CM-induced mice were tested behaviorally (elevated plus maze, rota rod test, and hanging wire test), biochemically (nitric oxide estimation, cytokines (IL-1, IL-6, IL-10, IL-12p70, TNF, IFN-y), histopathologically and immunohistochemically, and finally ultrastructural changes were examined using a transmission electron microscope. All three chalcones treated groups showed a significant (p < 0.001) decrease in percentage parasitemia at the 10th day post-infection. Mild anxiolytic activity of chalcones as compared to standard treatment with quinine has been observed during behavior tests. No pigment deposition was observed in the QNN-T group and other chalcone derivative treated groups. Rosette formation was seen in the derivative 1 treated group. The present derivatives may be pioneered by various research and science groups to design such a scaffold that will be a future antimalarial with therapeutic potential or, because of its immunomodulatory properties, it could be used as an adjunct therapy. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-023-03676-y.

Antimalarial and immunomodulatory potential of chalcone derivatives in experimental model of malaria.

BACKGROUND: Malaria is a complex issue due to the availability of few therapies and chemical families against Plasmodium and mosquitoes. There is increasing resistance to various drugs and insecticides in Plasmodium and in the vector. Additionally, human behaviors are responsible for promoting resistance as well as increasing the risk of exposure to infections. Chalcones and their derivatives have been widely explored for their antimalarial effects. In this context, new derivatives of chalcones have been evaluated for their antimalarial efficacy. METHODS: BALB/c mice were infected with P. berghei NK-65. The efficacy of the three most potent chalcone derivations (1, 2, and 3) identified after an in vitro compound screening test was tested. The selected doses of 10 mg/kg, 20 mg/kg, and 10 mg/kg were studied by evaluating parasitemia, changes in temperature, body weights, organ weights, histopathological features, nitric oxide, cytokines, and ICAM-1 expression. Also, localization of parasites inside the two vital tissues involved during malaria infections was done through a transmission electron microscope. RESULTS: All three chalcone derivative treated groups showed significant (p < 0.001) reductions in parasitemia levels on the fifth and eighth days of post-infection compared to the infected control. These derivatives were found to modulate the immune response in a P. berghei infected malaria mouse model with a significant reduction in IL-12 levels. CONCLUSIONS: The present study indicates the potential inhibitory and immunomodulatory actions of chalcones against the rodent malarial parasite P. berghei.

Binding Expedient of 2-carbamido-1,3-indandione to Nucleic Acids: Potential Fluorescent Probe.

Fluorescent and computational methods were used to elucidate the binding expedient of 2-carbamido-1,3-indandione (CAID) tautomers to nucleotides. The dependence of the fluorescence emission of CAID loaded nucleic acids sequences to compound concentration, temperature and time variation was investigated. It was found that the subject compound binds to nucleic acids but does not intercalate. According to our quantum-chemical calculations on the conjugation between CAID and nucleotides, the binding in the formed complexes may be through hydrogen bonds. Two possible types of complexes were considered-CAID to the phosphate group and CAID to the nucleobase. To estimate the binding affinity, the interaction energies of the formed complexes were calculated. Tautomer 2-carboamide-1-hydroxy-3-oxo-indane is preferred in the formation of complexes, and the phosphate group complexes were more stable. Generally, the guanosine and deoxyguanosine monophosphate complexes were the most preferred regardless of the complex type. Because of the lack of cytotoxic effect on untransformed cell lines of mouse embryo fibroblasts Balb/c 3T3 according to our previous report (Markova et al, (2017) Bulg Chem Commun, 49D, 221-226) and the affinity to nucleic acids, we can suggest that the subject compound could be suitable to be used as a novel type of fluorescent biomarker.

Chemical evolution: from formamide to nucleobases and amino acids without the presence of catalyst.

Abiotic synthesis of nucleobases and amino acids is of critical importance as it sheds light on potential prebiotic chemical reactions. During thermal decomposition of formamide in vacuum conditions, purine, cytosine, adenine, hypoxanthine, uracil, pterin, urea, urocanic acid, glycine, alanine and norvaline were detected. The compounds were obtained without catalyst by heating at 100-180 °C or microwave heating of formamide. Reaction network of self-catalyzed chemical reactions is suggested, showing how from only one parent molecule, nucleobases, urea and the amino acid glycine can be produced. The reaction pathways are theoretically determined using SCS-MP2 calculations.Communicated by Ramaswamy H. Sarma.

Ultrastructural alterations in Plasmodium falciparum induced by chalcone derivatives.

OBJECTIVE: Chalcones (1, 3-diaryl-2-propen-1-ones) and their derivatives are widely explored from the past decade for its antimalarial activity. To elucidate their mechanism of action on the malaria parasite, the ultrastructural changes with the action of these derivatives in different organelles of the parasite were studied in vitro. Infected RBCs [CQ sensitive (MRC-2) and CQ resistant (RKL-9) Plasmodium strain] were treated with three chalcone derivatives 1, 2 and 3 and standard drugs, i.e., CQ and artemisinin at twice their respective IC50 values for 24 h and then harvested, washed, fixed, embedded and stained to visualize ultra-structure changes before and after intervention of treatment under in vitro condition through transmission electron microscope. RESULTS: The ultrastructural changes demonstrate the significant disturbance of all parasite membranes, including those of the nucleus, mitochondria and food vacuole, in association with a marked reduction of ribosomes in the trophozoites and cessation of developing schizonts which suggest multiple mechanisms of action by which chalcone derivatives act on the malaria parasite. The present study opens up perspectives for further exploration of these derivatives in vivo malaria model to discover more about its effect and mechanism of action.

In vitro anti-malarial efficacy of chalcones: cytotoxicity profile, mechanism of action and their effect on erythrocytes.

BACKGROUND: Malaria extensively leads to mortality and morbidity in endemic regions, and the emergence of drug resistant parasites is alarming. Plant derived synthetic pharmaceutical compounds are found to be a foremost research to obtain diverse range of potent leads. Amongst them, the chalcone scaffold is a functional template for drug discovery. The present study involves synthesis of ten chalcones with various substitution pattern in rings A and B and assessment of their anti-malarial efficacy against chloroquine sensitive and chloroquine resistant strains as well as of their cytotoxicity and effect on haemozoin production. METHODS: The chalcones were synthesized by Claisen-Schmidt condensation between equimolar quantities of substituted acetophenones and aryl benzaldehydes (or indole-3-carboxaldehyde) and were screened for anti-malarial activity by WHO Mark III schizont maturation inhibition assay. The cytotoxicity profile of a HeLa cell line was evaluated through MTT viability assay and the selectivity index (SI) was calculated. Haemozoin inhibition assay was performed to illustrate mode of action on a Plasmodium falciparum strain. RESULTS: The IC50 values of all compounds were in the range 0.10-0.40 µg/mL for MRC-2 (a chloroquine sensitive strain) and 0.14-0.55 µg/mL for RKL-9 (a chloroquine resistant strain) of P. falciparum. All the chalcones showed low cellular toxicity with minimal haemolysis. The statistically significant reduction (p < 0.05) in the haemozoin production suggests a similar mechanism than that of chloroquine. CONCLUSIONS: Out of ten chalcones, number 7 was found to be a lead compound with the highest potency (IC50 = 0.11 µg/mL), as compared to licochalcone (IC50 = 1.43 µg/mL) and with high selectivity index of 85.05.

Synthesis, Characterization, Quantum-Chemical Calculations and Cytotoxic Activity of 1,8-Naphthalimide Derivatives with Non-Protein Amino Acids.

BACKGROUND: The 1,8-Naphthalimides constitute an important class of biologically active, DNAbinding compounds. There are no available data on the synthesis of 1,8-naphthalimide derivatives with nonprotein amino acids and their biological activity. The aim of this paper was to determine the synthesis, structural characterization and cytotoxic activity of new 1-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)cycloalkane-1- carboxylic acids with 5-, 6-, 7-, 8- and 12-membered rings as well as 2-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)- yl)adamantane-2-carboxylic acid and 1-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)-1,2,3,4-tetrahydronaphthalene- 1-carboxylic acid. METHODS: The target compounds were obtained by an interaction of 1,8-naphthalic anhydride with a series of non-protein amino acids. The optimized geometry and harmonic vibrational frequencies have been calculated by DFT employing B3LYP functional using 6-31G(d,p) basis set. An ab initio (MP2 and Hartee-Fock) and DFT (different functionals) using several basis sets have been applied for NMR calculations. The cytotoxic effects of the synthesized compounds are assessed against two human tumor cell lines, namely K-562 (chronic myeloid leukemia) and HUT-78 (cutaneous T-cell lymphoma) after 72 h exposure, using the MTT-dye reduction assay. The apoptogenic effects and the ability to modulate the NFκB-signaling pathways were determined using commercially available ELISA kits. RESULTS: All compounds inhibited the growth of malignant cells at micromolar concentrations whereby compound 4b (1-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)cyclohexane-1-carboxylic acid) demonstrated superior activity in both cell lines with IC50 values comparable to those of the reference anticancer drug melphalan. CONCLUSION: New 1,8-naphthalimide derivatives with non-protein amino acids were successfully synthesized. Quantum-chemical calculations were performed to elucidate the structure of the newly synthesized compounds. There is a proper alignment between theoretical and experimental results. The cytotoxicity of the synthesized products against two human tumor cell lines, namely K-562 and HUT-78 was evaluated. All compounds inhibited the growth of malignant cells at micromolar concentrations. The pharmacodynamics evaluation of compound 4b showed that its cytotoxicity is mediated by induction of apoptosis and inhibition of NFκB-signaling.

Tautomerism of Inosine in Water: Is It Possible?

Syn- and anti-conformers of four tautomer structures of inosine were studied in the gas phase and in solvent water to investigate the possibility of hydrogen bonding and tautomeric conversion. It was found that in the gas phase and in water solution the most stable is the syn-conformer of the 6-keto tautomer followed by its anti-conformer and syn-conformer of the 6-enol form. In the gas phase, the percent content of syn- and anti-conformers is 83.77 and 12.86%, respectively, whereas syn-enol tautomer is calculated to be 2.54%. However, in water solution the syn-conformer of the keto tautomer is 99.9%. The water-assisted proton transfer process in inosine was investigated using ab initio MP2 and SCS-MP2 quantum chemical approaches. Solute-solvent clusters containing an inosine molecule and five water molecules embedded in the "bulk" solvent treated as polarizable continuum (the CPCM/MP2/6-31+G(d,p) level of theory) were explored. The energy barrier of the water-assisted proton transfer reaction in inosine is found to be 12.9 kcal mol-1 and the rate constant ( k = 6.68 × 101 s-1) is sufficiently large to generate the 6-enol tautomer. From the reaction profile of the proton transfer we can conclude that the process is realized through the asynchronous concerted mechanism.

Hybrid MC/QC simulations of water-assisted proton transfer in nucleosides. Guanosine and its analog acyclovir.

To provide an in-depth insight into the molecular basis of spontaneous tautomerism in DNA and RNA base pairs, a hybrid Monte Carlo (MC)-quantum chemical (QC) methodology is implemented to map two-dimensional potential energy surfaces along the reaction coordinates of solvent-assisted proton transfer processes in guanosine and its analog acyclovir in aqueous solution. The solvent effects were simulated by explicit inclusion of water molecules that model the relevant part of the first hydration shell around the solute. The position of these water molecules was estimated by carrying out a classical Metropolis Monte Carlo simulation of dilute water solutions of the guanosine (Gs) and acyclovir (ACV) and subsequently analyzing solute-solvent intermolecular interactions in the statistically-independent MC-generated configurations. The solvent-assisted proton transfer processes were further investigated using two different ab initio MP2 quantum chemical approaches. In the first one, potential energy surfaces of the 'bare' finite solute-solvent clusters containing Gs/ACV and four water molecules (MP2/6-31+G(d,p) level) were explored, while within the second approach, these clusters were embedded in 'bulk' solvent treated as polarizable continuum (C-PCM/MP2/6-31+G(d,p) level of theory). It was found that in the gas phase and in water solution, the most stable tautomer for guanosine and acyclovir is the 1H-2-amino-6-oxo form followed by the 2-amino-6-(sZ)-hydroxy form. The energy barriers of the water-assisted proton transfer reaction in guanosine and in acyclovir are found to be very similar - 11.74 kcal mol-1 for guanosine and 11.16 kcal mol-1 for acyclovir, and the respective rate constants (k = 1.5 × 101 s-1, guanosine and k = 4.09 × 101 s-1, acyclovir), are sufficiently large to generate the 2-amino-6-(sZ)-hydroxy tautomer. The analysis of the reaction profiles in both compounds shows that the proton transfer processes occur through the asynchronous concerted mechanism.

Anti-conjunctivitis effect of fresh juice of xGraptoveria (Crassulaceae): A phytochemical and ethnobotanical study.

AIM: The parent of xGraptoveria, Graptopetalum paraguayense, is used in Chinese folk medicine for alleviating hepatic disorders, detumescence and detoxication, lowering of blood pressure, inhibition of cancer cells, exerting diuretic effects, relieving pain and infections. No data are available regarding its anti-conjunctivitis effect. The aim of this preliminary study is to test the anti-conjunctivitis properties of xGraptoveria (Crassulaceae) and to identify its bioactive constituents. MATERIALS AND METHODS: Fresh watery juice of leaves of xGraptoveria was extracted with n-butanol and the extract was analyzed using gas chromatography-mass spectrometry (GC/MS). The ethnobotanical appraisal of the anti-conjunctivitis properties of xGraptoveria was based on 11 interviews about the symptoms against which this plant demonstrated positive effect. RESULTS: Fresh juice of xGraptoveria leaves applied directly to the irritated eye 2 times per day cured conjunctivitis in all reported cases. The main groups of organic compounds identified by GC/MS analysis in the fresh extracted leaf juice of xGraptoveria were: Alkylamines, hydroxycarboxylic acids, aliphatic and aromatic carboxylic acids, amino acids, alcohols, aromatic and aliphatic hydrocarbons. CONCLUSION: In this preliminary study, it is suggested that xGraptoveria exerts anti-conjunctivitis activity, through synergistic effect of different chemical compounds, most probably alkylamines and mainly hydroxycarboxylic, aliphatic, and aromatic carboxylic acids.

2-Carbamido-1,3-indandione - a Fluorescent Molecular Probe and Sunscreen Candidate.

The present work reports theoretical and experimental studies on the photophysical properties of two tautomeric forms of 2-carbamido-1,3-indandione (CAID). By means of UV-vis, steady-state and time-dependent fluorescence spectroscopy it is shown that both enol forms, 2-(hydroxylaminomethylidene)-indan-1,3-dione and 2-carboamide-1-hydroxy-3-oxo-indan, coexist in solution. On the base of spectroscopic studies of CAID interaction with human serum albumin and DNA sequences, it was shown that the compound has potential and it is suitable for use as fluorescent molecular probe for investigation of different biomolecules. CAID shows relatively high photostability within 3 h irradiation period. Such behavior of the investigated compound supposes possibilities for using of the CAID molecule as sunscreen because of strong absorption in UVA, UVB and UVC light spectra.

Synthesis of 3',4'-dihydro-2H,2'H,5H-spiro [imidazolidine-4,1'-naphthalene]-2,5-dione and its derivatives.

The synthesis of two novel compounds, 1-amino-3',4'-dihydro-2H,2'H,5H-spiro[imidazolidine-4,1'-naphthalene]-2,5-dione and 1,3-bis(hydroxymethyl)-3',4'-dihydro-2H,2'H,5H-spiro[imidazolidine-4,1'-naphthalene]-2,5-dione, was reported. The structures of the compounds were verified by (1)H, (13)C NMR and IR spectroscopy and quantum-chemical calculations at DFT level.

Tautomeric equilibria of 5-fluorouracil anionic species in water.

It has long been postulated that rare tautomeric or ionized forms of nucleic acid bases may play a role in mispair formation. Therefore, ab initio quantum chemical investigations on the tautomeric equilibrium in 5-fluorouracil (5FU) and its anions (deprotonated from N1, AN1, and from N3, AN3) and their tautomeric forms in water were performed. The effect of the water as solvent was introduced using solute-solvent clusters (four water molecules). The influence of the water molecules on the tautomeric reactions between different forms was considered by multiple proton transfer mechanisms. We show that when a water dimer is located in the reaction site between the two pairs of N-H and C═O groups, the assistive effect of the water molecules is strengthened. All calculations of the solute-water complexes were carried out at an MP2 level of theory and supplemented with correction for higher order correlation terms at CCSD(T) level, using the 6-31+G(d,p) basis set. The ab initio calculated frequencies and Raman intensities of 5FU and its anions AN1, AN3, and dianion are in good agreement with the experimental Raman frequencies in aqueous solution at different pH. In order to establish the pH-induced structural transformation in the molecule of 5FU, further (1)H, (19)F, and (13)C NMR spectra in water solution for pH = 6.9-13.8 were acquired and the chemical shift alterations were determined as a function of pH. On the basis of NMR spectroscopic data obtained for 5FU in aqueous solution at alkaline pH, we suggest the existence of a mixture of the anionic tautomeric forms predicted by our theoretical calculations.

Physicochemical characterization and in vitro behavior of daunorubicin-loaded poly(butylcyanoacrylate) nanoparticles.

The design, preparation and characterization of poly(butylcyanoacrylate) nanoparticles as a drug-delivery system for daunorubicin is reported. A range of light scattering [photon correlation spectroscopy (PCS)], spectroscopic [(1)H nuclear magnetic resonance ((1)H NMR), Fourier transform infrared (FTIR), chromatographic [gel permeation chromatography (GPC)] and quantum chemical techniques have been employed for the physicochemical characterization of drug-loaded nanoparticles and to clarify the mechanisms of drug immobilization in the polymer matrix. The presence of daunorubicin in the polymerization medium was found to affect both the degree of polymerization and the compactness of the resulting nanoparticles. The GPC, FTIR and (1)H NMR results confirmed cytostatic immobilization in the polymer matrix, with evidence for the presence of three types of inclusion: physically entrapped, polymer-associated (due to hydrogen bonds and/or dipole-charge interactions with the polymer chains), and polymer surface-adsorbed daunorubicin. The developed colloidal delivery system has the capacity for sustained in vitro release of daunorubicin. Preliminary in vitro assays were carried out on two cell lines, DLKP and DLKP-A, which display different levels of drug resistance, to evaluate the cytotoxicity of the drug-loaded nanoparticles.

Ab initio investigation on the second-order nonlinear optical responses in keto-enol equilibria of salicylideneanilines.

The keto-enol (K-E) tautomerization equilibrium, more precisely, the keto-amine/enol-imine equilibrium, has been investigated for a series of substituted salicylideneanilines in view of designing compounds with a contrast of second-order nonlinear optical properties. Substituting the salicylidene ring by an acceptor group or the other ring by a donor prevents the K form from being stable, whereas in the other cases, the K form can easily be converted to the E form due to the small activation barrier, figuring out in most cases that the K form is metastable. For a representative set of donor/acceptor substituents, the E and K forms present a sufficiently large contrast of beta to allow its detection by using electric-field-induced second harmonic generation or hyper-Rayleigh scattering. The largest beta values are mainly associated with species bearing a donor in the para position of the salicylidene ring and an acceptor on the other ring whereas the largest beta values are generally found for the E form.

Oxo-hydroxy tautomerism of 5-fluorouracil: water-assisted proton transfer.

Post-Hartree-Fock ab initio quantum chemical calculations were performed for 5-fluorouracil in the gas phase and in a three-water cluster. Full geometry optimizations of the 5-fluorouracil-water complexes were carried out at the MP2/6-31+G(d,p) level of theory. MP4/6-31+G(d,p)//MP2/6-31+G(d,p) and MP4/6-31++G(d,p)//MP2/6-31+G(d,p) single-point calculations were performed to obtain more accurate energies. In water solution, 5-fluorouracil exists mainly in the 2,4-dioxo form (A). We propose that the populations of the 2-hydroxy-4-oxo (B) and 4-hydroxy-2-oxo (D) tautomers are 1 x 10(-4)% and 3.9 x 10(-8)%, respectively, on the basis of the relative stabilities of the tautomers calculated at the MP4/6-31++G(d,p)//MP2/6-31+G(d,p) level of theory. A profound difference between isolated and hydrated 5-fluorouracil is noted for the height of the tautomerization barrier. In the absence of water, the process of proton transfer is very slow. The addition of water molecules decreases the barrier by 2.3 times, making the process much faster. The minimum energy path (MP2/6-31+G(d,p)) for water-assisted proton transfer in trihydrated 5-fluorouracil was followed. CNDO/S-CI calculations predict singlet pi-pi(*) electron transitions at 312 nm for B and at 318 nm for D. The fluorescence spectrum of 5-fluorouracil in water confirms the presence of the hydroxy tautomer.

Ab initio study of 2,4-substituted azolidines. II. Amino-imino tautomerism of 2-aminothiazolidine-4-one and 4-aminothiazolidine-2-one in water solution.

The relative stabilities of the tautomers of 2-aminothiazolidine-4-one and 4-aminothiazolidine-2-one were calculated at the MP2/6-31+G(d,p) level by considering their mono- and trihydrated complexes. Single-point calculations at the MP4/6-31+G(d,p)//MP2/6-31+G(d,p) level of theory were performed to obtain more accurate energies. The values of proton transfer barriers in the isolated, mono- and trihydrated tautomers of 2-aminothiazolidine-4-one (2AT) and 4-aminothiazolidine-2-one (4AT) were calculated for two different mechanisms of tautomerisation. In the absence of water, the process of proton transfer should not occur. Addition of water molecules decreases the barrier making the process faster, as the participation of two water molecules in a proton transfer reaction is more favorable than the participation of only one water molecule. To estimate the effect of the medium (water) on the relative stabilities of the tautomers of the studied compounds we applied the polarizable continuum model (PCM). (13)C NMR chemical shieldings were calculated using the GIAO approach at MP2/6-31+G(d,p) optimized geometries. HF and the DFT B3LYP functional with 6-31+G(d,p) basis set were employed. The quantum chemical results for the chemical shifts in gas phase and in polar solvents (water and DMSO) were compared with experimental data. TD DFT B3LYP/aug-cc-pVTZ calculations were performed to predict the absorption maxima of tautomers A and B of 2AT and 4AT.