Novel hybrids of sclareol and 1,2,4-triazolo[1,5-a]pyrimidine show collateral sensitivity in multidrug-resistant glioblastoma cells.

The synthesis of 24 hybrid molecules, consisting of naturally occurring sclareol (SCL) and synthetic 1,2,4-triazolo[1,5-a]pyrimidines (TPs), is described. New compounds were designed with the aim of improving the cytotoxic properties, activity, and selectivity of the parent compounds. Six analogs (12a-f) contained 4-benzylpiperazine linkage, while 4-benzyldiamine linkage was present in eighteen derivatives (12g-r and 13a-f). Hybrids 13a-f consist of two TP units. After purification, all hybrids (12a-r and 13a-f), as well as their precursors (9a-e and 11a-c), were tested on human glioblastoma U87 cells. More than half of the tested synthesized molecules, 16 out of 31, caused a significant reduction of U87 cell viability (more than 75% reduction) at 30 µM. The concentration-dependent cytotoxicity of these 16 compounds was also examined on U87 cells, corresponding multidrug-resistant (MDR) U87-TxR cells with increased P-glycoprotein (P-gp) expression and activity, and normal lung fibroblasts MRC-5. Importantly, 12l and 12r were active in the nanomolar range, while seven compounds (11b, 11c, 12i, 12l, 12n, 12q, and 12r) were more selective towards glioblastoma cells than SCL. All compounds except 12r evaded MDR, showing even better cytotoxicity in U87-TxR cells. In particular, 11c, 12a, 12g, 12j, 12k, 12m, 12n, and SCL showed collateral sensitivity. Hybrid compounds 12l, 12q, and 12r decreased P-gp activity to the same extent as a well-known P-gp inhibitor - tariquidar (TQ). Hybrid compound 12l and its precursor 11c affected different cellular processes including the cell cycle, cell death, and mitochondrial membrane potential, and changed the levels of reactive oxygen and nitrogen species (ROS/RNS) in glioblastoma cells. Collateral sensitivity towards MDR glioblastoma cells was caused by the modulation of oxidative stress accompanied by inhibition of mitochondria.

Controlling Pd-Catalyzed N-Arylation and Dimroth Rearrangement in the Synthesis of N,1-Diaryl-1H-tetrazol-5-amines.

The Pd-catalyzed N-arylation method for the synthesis of eighteen N,1-diaryl-1H-tetrazol-5-amine derivatives is reported. By running the reactions at 35 °C, compounds were isolated as single isomers since the undesired Dimroth rearrangement was completely suppressed. Furthermore, the Dimroth rearrangement of N,1-diaryl-1H-tetrazol-5-amines was rationalized by conducting comprehensive experiments and NMR analysis as well as density functional theory (DFT) calculations of thermodynamic stability of the compounds. It was established that the Dimroth rearrangement is thermodynamically controlled, and the equilibrium of the reaction is determined by the stability of the corresponding isomers. The mechanism was investigated by additional DFT calculations, and the opening of the tetrazole ring was shown to be the rate-determining step. By maneuvering Pd-catalyzed N-arylation and the subsequent Dimroth rearrangement, two more N,1-diaryl-1H-tetrazol-5-amine derivatives were acquired, which otherwise cannot be synthesized by employing the C-N cross-coupling reaction.

Bis-guanylhydrazones as efficient anti-Candida compounds through DNA interaction.

Candida spp. are leading causes of opportunistic mycoses, including life-threatening hospital-borne infections, and novel antifungals, preferably aiming targets that have not been used before, are constantly needed. Hydrazone- and guanidine-containing molecules have shown a wide range of biological activities, including recently described excellent antifungal properties. In this study, four bis-guanylhydrazone derivatives (BG1-4) were generated following a previously developed synthetic route. Anti-Candida (two C. albicans, C. glabrata, and C. parapsilosis) minimal inhibitory concentrations (MICs) of bis-guanylhydrazones were between 2 and 15.6 µg/mL. They were also effective against preformed 48-h-old C. albicans biofilms. In vitro DNA interaction, circular dichroism, and molecular docking analysis showed the great ability of these compounds to bind fungal DNA. Competition with DNA-binding stain, exposure of phosphatidylserine at the outer layer of the cytoplasmic membrane, and activation of metacaspases were shown for BG3. This pro-apoptotic effect of BG3 was only partially due to the accumulation of reactive oxygen species in C. albicans, as only twofold MIC and higher concentrations of BG3 caused depolarization of mitochondrial membrane which was accompanied by the decrease of the activity of fungal mitochondrial dehydrogenases, while the activity of oxidative stress response enzymes glutathione reductase and catalase was not significantly affected. BG3 showed synergistic activity with amphotericin B with a fractional inhibitory concentration index of 0.5. It also exerted low cytotoxicity and the ability to inhibit epithelial cell (TR146) invasion and damage by virulent C. albicans SC5314. With further developments, BG3 may further progress in the antifungal pipeline as a DNA-targeting agent.

Consensus-based comparison of chromatographic and computationally estimated lipophilicity of benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs.

Lipophilicity is one of the essential properties influencing drug absorption, excretion and metabolism. It is used for screening viable drug candidates. Chromatographic behavior of thiepino[3,2-c:6,7-c']dipyridine and 16 benzothiepino[3,2-c]pyridine derivatives as potential antifungal drugs was studied using thin-layer chromatography under typical reversed-phase conditions and two microemulsion chromatographic systems. Seventeen chromatographic and nine in silico lipophilicity measures were estimated. They were compared by classical multivariate approaches: principal component analysis, hierarchical cluster analysis, and ranked and grouped by the non-parametric method-Sum of ranking differences. Two computational and two chromatographic descriptors from the typical reversed-phase conditions using acetone/water mixtures emerged as the best candidates for lipophilicity estimation. The principal component scores related to typical reversed-phase conditions using dioxane/water were ranked as statistically insignificant (the worst). Microemulsion systems were positioned in between, performing worse than in silico estimates. Thiepine derivatives were ranked and grouped by sum of ranking differences, fusing multiple lipophilicity measures. In multicriteria maximization ranking, the compound substituted by phenyl group at position 8 was selected as the most lipophilic one. It is also the most active against Candida albicans. The ranking confirmed that introduction of phenyl core is essential for increasing the lipophilicity of the studied compounds.

Synthesis and evaluation of thiophene-based guanylhydrazones (iminoguanidines) efficient against panel of voriconazole-resistant fungal isolates.

A series of new thiophene-based guanylhydrazones (iminoguanidines) were synthesized in high yields using a straightforward two-step procedure. The antifungal activity of compounds was evaluated against a wide range of medicaly important fungal strains including yeasts, molds, and dermatophytes in comparison to clinically used drug voriconazole. Cytotoxic properties of compounds were also determined using human lung fibroblast cell line and hemolysis assay. All guanylhydrazones showed significant activity against broad spectrum of clinically important species of Candida spp., Aspergillus fumigatus, Fusarium oxysporum, Microsporum canis and Trichophyton mentagrophytes, which was in some cases comparable or better than activity of voriconazole. More importantly, compounds 10, 11, 13, 14, 18 and 21 exhibited excellent activity against voriconazole-resistant Candida albicans CA5 with very low minimal inhibitory concentration (MIC) values <2 µg mL(-1). Derivative 14, bearing bromine on the phenyl ring, was the most effective compound with MICs ranging from 0.25 to 6.25 µg mL(-1). However, bis-guanylhydrazone 18 showed better selectivity in terms of therapeutic index values. In vivo embryotoxicity on zebrafish (Danio rerio) showed improved toxicity profile of 11, 14 and 18 in comparison to that of voriconazole. Most guanylhydrazones also inhibited C. albicans yeast to hyphal transition, essential for its biofilm formation, while 11 and 18 were able to disperse preformed Candida biofilms. All guanylhydrazones showed the equal potential to interact with genomic DNA of C. albicans in vitro, thus indicating a possible mechanism of their action, as well as possible mechanism of observed cytotoxic effects. Tested compounds did not have significant hemolytic effect and caused low liposome leakage, which excluded the cell membrane as a primary target. On the basis of computational docking experiments using both human and cytochrome P450 from Candida it was concluded that the most active guanylhydrazones had minimal structural prerequisites to interact with the cytochrome P450 14α-demethylase (CYP51). Promising guanylhydrazone derivatives also showed satisfactory pharmacokinetic profile based on molecular calculations.

Investigation into novel thiophene- and furan-based 4-amino-7-chloroquinolines afforded antimalarials that cure mice.

We herein report the design and synthesis of a novel series of thiophene- and furan-based aminoquinoline derivatives which were found to be potent antimalarials and inhibitors of ß-hematin polymerization. Tested compounds were 3-71 times more potent in vitro than CQ against chloroquine-resistant (CQR) W2 strain with benzonitrile 30 being as active as mefloquine (MFQ), and almost all synthesized aminoquinolines (22/27) were more potent than MFQ against multidrug-resistant (MDR) strain C235. In vivo experiments revealed that compound 28 showed clearance with recrudescence at 40 mg/kg/day, while 5/5 mice survived in Thompson test at 160 mg/kg/day.

Novel hybrid compounds of sclareol and doxorubicin as potential anticancer nanotherapy for glioblastoma.

Two novel hybrid compounds, CON1 and CON2, have been developed by combining sclareol (SC) and doxorubicin (DOX) into a single molecular entity. These hybrid compounds have a 1:1 molar ratio of covalently linked SC and DOX. They have demonstrated promising anticancer properties, especially in glioblastoma cells, and have also shown potential in treating multidrug-resistant (MDR) cancer cells that express the P-glycoprotein (P-gp) membrane transporter. CON1 and CON2 form nanoparticles, as confirmed by Zetasizer, transmission electron microscopy (TEM), and chemical modeling. TEM also showed that CON1 and CON2 can be found in glioblastoma cells, specifically in the cytoplasm, different organelles, nucleus, and nucleolus. To examine the anticancer properties, the U87 glioblastoma cell line, and its corresponding multidrug-resistant U87-TxR cell line, as well as patient-derived astrocytoma grade 3 cells (ASC), were used, while normal human lung fibroblasts were used to determine the selectivity. CON1 and CON2 exhibited better resistance and selectivity profiles than DOX, showing less cytotoxicity, as evidenced by real-time cell analysis, DNA damage determination, cell death induction, mitochondrial respiration, and mitochondrial membrane depolarization studies. Cell cycle analysis and the ß-galactosidase activity assay suggested that glioblastoma cells die by senescence following CON1 treatment. Overall, CON1 and CON2 showed great potential as they have better anticancer features than DOX. They are promising candidates for additional preclinical and clinical studies on glioblastoma.

Direct glyphosate soil monitoring at the triazine-based covalent organic framework with the theoretical study of sensing principle.

Covalent organic frameworks (COFs) are emerging as promising sensing materials due to their controllable structure and function properties, as well as excellent physicochemical characteristics. Here, specific interactions between a triazine-based COF and a mass-used herbicide - glyphosate (GLY) have been utilized to design a disposable sensing platform for GLY detection. This herbicide has been extensively used for decades, however, its harmful environmental impact and toxicity to humans have been recently proven, conditioning the necessity for the strict control and monitoring of its use and its presence in soil, water, and food. Glyphosate is an organophosphorus compound, and its detection in complex matrices usually requires laborious pretreatment. Here, we developed a direct, miniaturized, robust, and green approach for disposable electrochemical sensing of glyphosate, utilizing COF's ability to selectively capture and concentrate negatively charged glyphosate molecules inside its nanopores. This process generates the concentration gradient of GLY, accelerating its diffusion towards the electrode surface. Simultaneously, specific COF-glyphosate binding catalyses the oxidative cleavage of the C-P bond and, together with pore nanoconfinement, enables sensitive glyphosate detection. Detailed sensing principles and selectiveness were scrutinized using DFT-based modelling. The proposed electrochemical method has a linear working range from 0.1 µM to 10 µM, a low limit of detection of 96 nM, and a limit of quantification of 320 nM. The elaborated sensing approach is viable for use in real sample matrices and tested for GLY determination in soil and water samples, without pretreatment, preparation, or purification. The results showed the practical usefulness of the sensor in the real sample analysis and suggested its suitability for possible out-of-laboratory sensing.

Unraveling the anti-virulence potential and antifungal efficacy of 5-aminotetrazoles using the zebrafish model of disseminated candidiasis.

Candida albicans remains the main causal agent of candidiasis, the most common fungal infection with disturbingly high mortality rates worldwide. The limited diversity and efficacy of clinical antifungal drugs, exacerbated by emerging drug resistance, have resulted in the failure of current antifungal therapies. This imposes an urgent demand for the development of innovative strategies for effective eradication of candidal infections. While the existing clinical drugs display fungicidal or fungistatic activity, the strategy specifically targeting C. albicans filamentation, as the most important virulence trait, represents an attractive approach for overcoming the drawbacks related to clinical antifungals. The results acquired in this study revealed the significant potential of 5-aminotetrazoles as a new class of effective and safe anti-virulence agents. Moreover, these novel agents were active when applied both alone and in combination with clinically approved polyenes. Complete prevention of C. albicans morphogenetic yeast-to-hyphae transition was achieved at doses as low as 1.3 µM under conditions mimicking various filamentation-responsive stimuli in the human body, while no cardio- or hepatotoxicity was observed at doses as high as 200 µM. The treatment of C. albicans-infected zebrafish embryos with nystatin alone had low efficacy, while the combination of nystatin and selected 5-aminotetrazoles prevented fungal filamentation, successfully eliminating the infection and rescuing the infected embryos from lethal disseminated candidiasis. In addition, the most potent anti-virulence 5-aminotetrazole prevented C. albicans in developing the resistance to nystatin when applied in combination, keeping the fungus sensitive to the antifungal drug.

Aminoquinolines afford resistance to cerebral malaria in susceptible mice.

OBJECTIVES: Malaria treatment is impeded by increasing resistance to conventional antimalarial drugs. Here we explored the activity of ten novel benzothiophene, thiophene and benzene aminoquinolines. METHODS: In vitro testing was performed by the lactate dehydrogenase assay in chloroquine (CQ)-sensitive Plasmodium falciparum strain 3D7 and CQ-resistant (CQR) P. falciparum strain Dd2. In vivo activity was evaluated by a modified Thompson test using C57BL/6 mice infected with Plasmodium berghei ANKA strain. RESULTS: Nine of the ten compounds had a lower 50% inhibitory concentration (IC50) than CQ against the CQR strain Dd2. Five of these compounds that were available for in vivo evaluation were shown to be non-toxic. All five compounds administered at a dose of 160mg/kg/day for 3 days prolonged the survival of treated compared with untreated mice. Untreated control mice died by Day 7 with a mean parasitaemia of 15%. Among treated mice, a dichotomous outcome was observed, with a two-third majority of treated mice dying by Day 17 with a low mean parasitaemia of 5%, whilst one-third survived longer with a mean hyperparasitaemia of 70%; specifically, five of these mice survived a mean of 25 days, whilst two even survived past Day 31. CONCLUSIONS: The significant antimalarial potential of this aminoquinoline series is illustrated by its excellent in vitro activity against the CQRP. falciparum strain and significant in vivo activity. Interestingly, compounds ClAQ7, ClAQ9 and ClAQ11 were able to confer resistance to cerebral malaria and afford a switch to hyperparasitaemia to mice prone to the neurological syndrome.

Chemo- and biocatalytic esterification of marchantin A and cytotoxic activity of ester derivatives.

Chemical and biocatalytic synthesis of seven previously undescribed marchantin A ester derivatives has been presented. Chemical synthesis afforded three peresterified bisbibenzyl products (TE1-TE3), while enzymatic method, using lipase, produced regioselective monoester derivatives (ME1-ME4). The antiproliferative activities of all prepared derivatives of marchantin A were tested on MRC-5 healthy human lung fibroblast, A549 human lung cancer, and MDA-MB-231 human breast cancer cell lines. All tested esters were less cytotoxic in comparison to marchantin A, but they also exhibited lower cytotoxicity against healthy cells. Monoesters displayed higher cytotoxic activities than the corresponding peresterified products, presumably due to the presence of free catechol group. Monohexanoyl ester ME3 displayed the same IC50 like marchantin A against MDA-MB-231 cells, but the selectivity was higher. In this way, regioselective enzymatic monoesterification enhanced selectivity of marchantin A. ME3 was also the most active among all derivatives against lung cancer cells A549 with the slightly lower activity and selectivity in comparison to marchantin A.

Development of an efficient biocatalytic system based on bacterial laccase for the oxidation of selected 1,4-dihydropyridines.

Biocatalytic oxidations mediated by laccases are gaining importance due to their versatility and beneficial environmental effects. In this study, the oxidation of 1,4-dihydropyridines has been performed using three different types of bacterial laccase-based catalysts: purified laccase from Bacillus licheniformis ATCC 9945a (BliLacc), Escherichia coli whole cells expressing this laccase, and bacterial nanocellulose (BNC) supported BliLacc catalysts. The catalysts based on bacterial laccase were compared to the commercially available Trametes versicolor laccase (TvLacc). The oxidation product of 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate was obtained within 7-24 h with good yields (70-99%) with all three biocatalysts. The substrate scope was examined with five additional 1,4-dihydropyridines, one of which was oxidized in high yield. Whole-cell biocatalyst was stable when stored for up to 1-month at 4 °C. In addition, evidence has been provided that multicopper oxidase CueO from the E. coli expression host contributed to the oxidation efficiency of the whole-cell biocatalyst. The immobilized whole-cell biocatalyst showed satisfactory activity and retained 37% of its original activity after three biotransformation cycles.

Aromatic Guanylhydrazones for the Control of Heme-Induced Antibody Polyreactivity.

In a healthy immune repertoire, there exists a fraction of polyreactive antibodies that can bind to a variety of unrelated self- and foreign antigens. Apart from naturally polyreactive antibodies, in every healthy individual, there is a fraction of antibody that can gain polyreactivity upon exposure to porphyrin cofactor heme. Molecular mechanisms and biological significance of the appearance of cryptic polyreactivity are not well understood. It is believed that heme acts as an interfacial cofactor between the antibody and the newly recognized antigens. To further test this claim and gain insight into the types of interactions involved in heme binding, we herein investigated the influence of a group of aromatic guanylhydrazone molecules on the heme-induced antibody polyreactivity. From the analysis of SAR and the results of UV-vis absorbance spectroscopy, it was concluded that the most probable mechanism by which the studied molecules inhibit heme-mediated polyreactivity of the antibody is the direct binding to heme, thus preventing heme from binding to antibody and/or antigen. The inhibitory capacity of the most potent compounds was substantially higher than that of chloroquine, a well-known heme binder. Some of the guanylhydrazone molecules were able to induce polyreactivity of the studied antibody themselves, possibly by a mechanism similar to heme. Results described here point to the conclusion that heme indeed must bind to an antibody to induce its polyreactivity, and that both π-stacking interactions and iron coordination contribute to the binding affinity, while certain structures, such as guanylhydrazones, can interfere with these processes.

Production of bacterial nanocellulose (BNC) and its application as a solid support in transition metal catalysed cross-coupling reactions.

Bacterial nanocellulose (BNC) emerged as an attractive advanced biomaterial that provides desirable properties such as high strength, lightweight, tailorable surface chemistry, hydrophilicity, and biodegradability. BNC was successfully obtained from a wide range of carbon sources including sugars derived from grass biomass using Komagataeibacter medellinensis ID13488 strain with yields up to 6 g L-1 in static fermentation. Produced BNC was utilized in straightforward catalyst preparation as a solid support for two different transition metals, palladium and copper with metal loading of 20 and 3 wt%, respectively. Sustainable catalysts were applied in the synthesis of valuable fine chemicals, such as biphenyl-4-amine and 4'-fluorobiphenyl-4-amine, used in drug discovery, perfumes and dye industries with excellent product yields of up to 99%. Pd/BNC catalyst was reused 4 times and applied in two consecutive reactions, Suzuki-Miyaura cross-coupling reaction followed by hydrogenation of nitro to amino group while Cu/BNC catalyst was examined in Chan-Lam coupling reaction. Overall, the environmentally benign process of obtaining nanocellulose from biomass, followed by its utilisation as a solid support in metal-catalysed reactions and its recovery has been described. These findings reveal that BNC is a good support material, and it can be used as a support for different catalytic systems.

Chemical stability of the peroxide bond enables diversified synthesis of potent tetraoxane antimalarials.

Of 17 prepared 1,2,4,5-tetraoxacyclohexanes stable to reductive and acidic conditions, 3 of them were more active than artemisinin against CQ and MFQ resistant strain TM91C235 and all compounds were more active in vitro against W2 than against D6 strain. In vivo, amines 10 and 11a cured all mice at higher doses with MCD < or = 37.5 (mg/kg)/day. Triol 13 was exceptionally active against melanoma (LOX IMVI) and ovarian cancer (IGROV1), both with LC 50 = 60 nM.

Benzothiazole carbamates and amides as antiproliferative species.

A series of new benzothiazole-based carbamates and amides were synthesized and their antiproliferative activity was determined. Derivatives with profound activity were identified and further investigated for their possible mechanism of action. It was found that these compounds induce specific apoptosis, G2/M cell cycle arrest and decrease ROS level in MCF-7 human breast cancer cell line. Moreover, submicromolar antiproliferative activity of examined carbamates against NT2/D1 testicular embryonal carcinoma was shown. The most potent derivatives strongly inhibited NT2/D1 cell migration and invasiveness.

Mononuclear silver(I) complexes with 1,7-phenanthroline as potent inhibitors of Candida growth.

Mononuclear silver(I) complexes with 1,7-phenanthroline (1,7-phen), [Ag(NO3-O,O') (1,7-phen-N7)2] (1) and [Ag(1,7-phen-N7)2]X, X = ClO4- (2), CF3SO3- (3), BF4- (4) and SbF6- (5) were synthesized and structurally characterized by NMR (1H and 13C), IR and UV-Vis spectroscopy and ESI mass spectrometry. The crystal structures of 1, 3 and 4 were determined by single-crystal X-ray diffraction analysis. In all these complexes, 1,7-phen coordinates to the Ag(I) ion in a monodentate fashion via the less sterically hindered N7 nitrogen atom. The investigation of the solution stability of 1-5 in DMSO revealed that they are sufficiently stable in this solvent at room temperature. Complexes 1-5 showed selectivity towards Candida spp. in comparison to bacteria, effectively inhibiting the growth of four different Candida species with minimal inhibitory concentrations (MIC) between 1.2 and 11.3 µM. Based on the lowest MIC values and the lowest cytotoxicity against healthy human fibroblasts with selectivity index of more than 30, the antifungal potential was examined in detail for the complex 1. It had the ability to attenuate C. albicans virulence and to reduce epithelial cell damage in the cell infection model. Induction of reactive oxygen species (ROS) response has been detected in C. albicans, with fungal DNA being one of the possible target biomolecules. The toxicity profile of 1 in the zebrafish model (Danio rerio) revealed improved safety and activity in comparison to that of clinically utilized silver(I) sulfadiazine.

Human serum albumin binding of certain antimalarials.

Interactions between eight in-house synthesized aminoquinolines, along with well-known chloroquine, and human serum albumin (HSA) have been studied by fluorescence spectroscopy. The synthesized aminoquinolines, despite being structurally diverse, were found to be very potent antimalarials. Fluorescence measurements indicate that three compounds having additional thiophene or benzothiophene substructure bind more strongly to HSA than other studied compounds. Competitive binding experiments indicate that these three compounds bind significantly stronger to warfarin compared to diazepam binding site. Fluorescence quenching at three temperatures (20, 25, and 37°C) was analyzed using classical Stern-Volmer equation, and a static quenching mechanism was proposed. The enthalpy and entropy changes upon sulphur-containing compound-HSA interactions were calculated using Van't Hoff equation. Positive values of enthalpy and entropy changes indicate that non-specific, hydrophobic interactions are the main contributors to HSA-compound interaction. Molecular docking and calculated lipophilicity descriptors indicate the same, pointing out that the increased lipophilicity of sulphur-containing compounds might be a reason for their better binding to HSA. Obtained results might contribute to design of novel derivatives with improved pharmacokinetic properties and drug efficacy.

Tetraoxane antimalarials and their reaction with Fe(II).

Mixed tetraoxanes 5a and 13 synthesized from cholic acid and 4-oxocyclohexanecarboxylic acid were as active as artemisinin against chloroquine-susceptible, chloroquine-resistant, and multidrug-resistant Plasmodium falciparum strains (IC50, IC90). Most active 13 is metabolically stable in in vitro metabolism studies. In vivo studies on tetraoxanes with a C(4' ') methyl group afforded compound 15, which cured 4/5 mice at 600 and 200 mg.kg-1.day-1, and 2/5 mice at 50 mg.kg-1.day-1, showing no toxic effects. Tetraoxane 19 was an extremely active antiproliferative with LC50 of 17 nM and maximum tolerated dose of 400 mg/kg. In Fe(II)-induced scission of tetraoxane antimalarials only RO* radicals were detected by EPR experiments. This finding and the indication of Fe(IV)=O species led us to propose that RO* radicals are probably capable of inducing the parasite's death. Our results suggest that C radicals are possibly not the only lethal species derived from peroxide prodrug antimalarials, as currently believed.

Quantitative structure retention/activity relationships of biologically relevant 4-amino-7-chloroquinoline based compounds.

The chromatographic behaviour of series of 4-amino-7-chloroquinoline (4,7-ACQ) based compounds was studied by reversed-phase thin-layer chromatography (RPTLC) with binary mobile phases containing water and the organic modifiers, DMSO or acetone. The lipophilicity of the studied compounds was determined by extrapolation of retention parameters RM to pure water content in mobile phase. In order to obtain some basic insight into the chromatographic behaviour and structural features of investigated compounds, PCA was performed on both chromatographic data (RM values) and calculated 2D and 3D structural descriptors. Both QSRR and QSAR models were built by means of the partial least squares (PLS) statistical method. It was found that descriptors which encode hydrophobic (dispersive) interactions have positive influence on retention, while influence of descriptors encoding polar interactions was negative. According to the obtained PLS model for inhibition of botulinum neurotoxin serotype A light chain, hydrophobic interactions influence positively on the mechanism of action of the investigated 4,7-ACQ, while polar interactions are less favoured. Contrary, the results of PLS modelling of activity against Plasmodium falciparum strains (W2, D6 and TM91C235) indicate that higher polarity of 4,7-ACQ contribute to their higher antimalarial activity.