Antiplasmodial hirsutinolides from Vernonia staehelinoides and their utilization towards a simplified pharmacophore

The dichloromethane extract of the leaves of Vernonia staehelinoides Harv. (Asteraceae) showed in vitro activity (IC(50) approximately 3 microg/ml) against the chloroquine-sensitive (D10) and the chloroquine-resistant (K1) strains of Plasmodium falciparum. Through conventional chromatographic techniques and bioassay-guided fractionation two structurally-related hirsutinolides displaying in vitro antiplasmodial activity (IC(50) approximately 0.2 microg/ml against D10) were isolated and identified by spectroscopic data. Compounds 1, 8 alpha-(2-methylacryloyloxy)-3-oxo-1-desoxy-1,2-dehydrohirsutinolide-13-O-acetate, and 2, 8 alpha-(5'-acetoxysenecioyloxy)-3-oxo-1-desoxy-1,2-dehydrohirsutinolide-13-O-acetate were found to be cytotoxic to mammalian Chinese Hamster Ovarian (CHO) cells at similar concentrations but proved to be attractive scaffolds for structure-activity relationship studies. Two main privileged substructures, a 2(5H)-furanone unit and a dihydrofuran-4-one unit, were identified as potential pharmacophores which may be responsible for the observed biological activity. Mucochloric and mucobromic acids were selected as appropriate 2(5H)-furanone substructures and these were shown to have comparable activity against the D10 and superior activity against the K1 strains relative to the hirsutinolide natural product. Mucochloric and mucobromic acids also show selective cytotoxicity to the malaria parasites compared to mammalian (CHO) cells in vitro. The antiplasmodial data obtained in respect of these two acids suggests that the 2(5H)-furanone substructure is a key pharmacophore in the observed antiplasmodial activity.     

Comparative antiplasmodial, leishmanicidal and antitrypanosomal activities of several biflavonoids

The antiplasmodial, leishmanicidal and antitrypanosomal activities of eight natural biflavonoids were estimated in vitro on a chloroquine-resistant strain of Plasmodium falciparum, axenically grown Leishmania donovani amastigotes and Trypanosoma cruzi trypomastigotes and Trypanosoma brucei rhodesiense bloodstream forms. Lanaroflavone showed the highest antiplasmodial activity (IC(50) = 0.48 microM), isoginkgetin was the most active leishmanicidal compound (IC(50) = 1.9 microM), whereas ginkgetin (IC(50) = 11 microM) and isoginkgetin (IC(50) = 13 microM) showed the best antitrypanosomal activity in our assays. The cytotoxicity and the selectivity indices for the most active compounds were also estimated. Lanaroflavone exhibited a high selectivity index value (SI = 159), indicating selective antiplasmodial activity.     

The antiplasmodial activity of norcantharidin analogs

The antiplasmodial activities of sixty norcantharidin analogs were tested in vitro against a chloroquine sensitive (D6, Sierra Leone) and chloroquine resistant (W2) strains of Plasmodium falciparum. Forty analogs returned IC(50) values <500 μM against at least one of the P. falciparum strains examined. The ring open compound 24 ((1S,4R)-3-(allylcarbamoyl)-7-oxabicyclo[2.2.1]heptane-2-carboxylic acid) is the most active aliphatic analog (D6 IC(50)=3.0±0.0 and W2 IC(50)=3.0±0.8 μM) with a 20-fold enhancement relative to norcantharidin. Surprisingly, seven norcantharimides also displayed good antiplasmodial activity with the most potent, 5 returning D6=8.9±0.9 and W2 IC(50)=12.5±2.2 μM, representing a fivefold enhancement over norcantharidin.     

Synthesis of totarol amino alcohol derivatives and their antiplasmodial activity and cytotoxicity

The previously unknown antiplasmodial activity of the plant derived natural product totarol is reported. Novel beta-amino alcohol derivatives based on this natural product were designed, synthesised and evaluated for in vitro antiplasmodial activity and cytotoxicity. These derivatives showed antiplasmodial IC50 values in the range of 0.6-3.0 microM and were equally active against a chloroquine-sensitive and resistant strain of Plasmodium falciparum, while showing little cytotoxicity against a mammalian cell line (CHO). In terms of lead development, two of the compounds based on substituted phenylpiperazine warrant further investigation as potential antiplasmodial leads. In addition to their selective antiplasmodial activity and lack of chloroquine cross-resistance, these compounds are structurally different to any of the available antimalarial drugs.     

Antiplasmodial and antifungal activities of iridal,a plant triterpenoid

Iridal, a triterpenoidic compound extracted from Iris germanica L., was previously shown to have an interesting activity on two cultured human tumor cell lines (A2780 and K562). In the present work, this same product was tested in vitro on Plasmodium falciparum chloroquine-resistant and -sensitive strains, in vivo on P. vinckei, and on some Candida albicans and C. parapsilosis strains too. The IC(50) obtained in vitro on human malaria strain ranged from 1.8 to 26.0 microg/ml and the ED(50) in vivo is about 85 mg/kg/day by intraperitoneal route. The minimal inhibitory concentrations were higher than to 50 microg/ml, whatever the strain of yeast tested. This product presents an antiplasmodial activity similar to that obtained with extracts from the plant Azadirachta indica classically taken as reference in malaria phytomedicine. Conversely iridal shows no important antifungal activity. The specific activity of iridal on human malaria parasite and on tumor cell lines is discussed.     

In vitro anti-malarial activity of N6-modified purine analogs

A library of N6-hydroxy-, methoxy-, or amino-adenosine analogs was prepared and screened for anti-malarial properties. We found three compounds that possess anti-plasmodial activity in the low micromolar range against the multi-drug resistant VS1 strain, namely N6-hydroxy-9H-purin-6-amine (IC50 5.57 micro M), 2-amino-N6-amino-adenosine (IC50 12.2 micro M), and 2-amino-N6-amino-N6-methyladenosine (IC50 0.29 micro M). More importantly, the compounds were non-toxic, with 2-amino-N6-amino-N6-methyladenosine showing a selectivity index of 5008.     

Role of single-electron oxidation potential and lipophilicity in the antiplasmodial in vitro activity of polyphenols: comparison to mammalian cells

In spite of extensive studies, the structure-activity relationships in the action of polyphenols against the malaria parasite Plasmodium falciparum are poorly understood so far. As the mammalian cell cytotoxicity of polyphenols shows a negative dependence on the potential of the phenoxyl radical/phenol redox couple (E(2)(7)), due to the involvement of prooxidant events, and a positive dependence on the octanol/water distribution coefficient at pH 7.0 (log D), we examined the role of these parameters in their antiplasmodial in vitro activity. We found that the concentrations of hydroxybenzenes causing 50% inhibition of the growth of P falciparum strain FcB1 (IC50) are described by the regression log IC50 (microM) = 0.36 + 1.81 E(2)(7) (V) - 0.10 log D [n = 11, r2 = 0.760, F(2.8) = 12.03]. The IC50 values of flavonoids (n = 5), comprising a separate less active series, did not depend on their E(2)(7) values, 0.33 V-0.75 V. These findings were similar to the mammalian cell cytotoxicity data. However, the mammalian cell cytotoxicity of hydroxybenzenes showed more pronounced dependence on their E(2)(7) values [delta log CL50/delta E(2)(7) = (6.9 - 5.1) V(-1), where CL50 is the compound concentration for 50% cell survival] than on their antiplasmodial activity. Although it is unclear whether the prooxidant action is the main factor in the antiplasmodial action of polyphenols or not, our data showed that the ease of their oxidation (decrease in E(2)(7)) may enhance their activity. On the other hand, the different sensitivity of the mammalian cell cytotoxicity and the antiplasmodial activity of the hydroxybenzenes to their E(2)(7) values implied that compounds with high oxidation potential may be used as relatively efficient antiplasmodial agents with low mammalian cell cytotoxicity.     

Benzoxazine derivatives of phytophenols show anti-plasmodial activity via sodium homeostasis disruption

Development of new class of anti-malarial drugs is an essential requirement for the elimination of malaria. Bioactive components present in medicinal plants and their chemically modified derivatives could be a way forward towards the discovery of effective anti-malarial drugs. Herein, we describe a new class of compounds, 1,3-benzoxazine derivatives of pharmacologically active phytophenols eugenol (compound 3) and isoeugenol (compound 4) synthesised on the principles of green chemistry, as anti-malarials. Compound 4, showed highest anti-malarial activity with no cytotoxicity towards mammalian cells. Compound 4 induced alterations in the intracellular Na⁺ levels and mitochondrial depolarisation in intraerythrocytic Plasmodium falciparum leading to cell death. Knowing P-type cation ATPase PfATP4 is a regulator for sodium homeostasis, binding of compound 3, compound 4 and eugenol to PfATP4 was analysed by molecular docking studies. Compounds showed binding to the catalytic pocket of PfATP4, however compound 4 showed stronger binding due to the presence of propylene functionality, which corroborates its higher anti-malarial activity. Furthermore, anti-malarial half maximal effective concentration of compound 4 was reduced to 490?nM from 17.54?µM with nanomaterial graphene oxide. Altogether, this study presents anti-plasmodial potential of benzoxazine derivatives of phytophenols and establishes disruption of parasite sodium homeostasis as their mechanism of action.     

Synthesis and biological screening of some pyridine derivatives as anti-malarial agents

Two series of pyridine derivatives were synthesised and evaluated for their in vivo anti-malarial activity against Plasmodium berghei. The anti-malarial activity was determined in vivo by applying 4-day standard suppressive test using chloroquine (CQ)-sensitive P. berghei ANKA strain-infected mice. Compounds 2a, 2g and 2h showed inhibition of the parasite multiplication by 90, 91 and 80%, respectively, at a dose level of 50 μmol/kg. Moreover, The most active compounds (2a, 2g and 2h) were tested in vitro against CQ-resistant Plasmodium falciparum RKL9 strains where compound 2g showed promising activity with IC(50)?=?0.0402 μM. The compounds were non-toxic at 300 and 100?mg/kg through the oral and parenteral routes, respectively. The docking pose of the most active compounds (2a, 2g and 2h) in the active site of dihydrofolate reductase enzyme revealed several hydrogen and hydrophobic interactions that contribute to the observed anti-malarial activities.     

Analysis of additivity and synergism in the anti-plasmodial effect of purified compounds from plant extracts

In the search for antimalarials from ethnobotanical origin, plant extracts are chemically fractionated and biological tests guide the isolation of pure active compounds. To establish the responsibility of isolated active compound(s) to the whole antiplasmodial activity of a crude extract, the literature in this field was scanned and results were analysed quantitatively to find the contribution of the pure compound to the activity of the whole extract. It was found that, generally, the activity of isolated molecules could not account on their own for the activity of the crude extract. It is suggested that future research should take into account the "drugs beside the drug", looking for those products (otherwise discarded along the fractionation process) able to boost the activity of isolated active compounds.     

4-Thiophenoxy-2-trichloromethyquinazolines display in vitro selective antiplasmodial activity against the human malaria parasite Plasmodium falciparum

A series of original quinazolines bearing a 4-thiophenoxy and a 2-trichloromethyl group was synthesized in a convenient and efficient way and was evaluated toward its in vitro antiplasmodial potential. The series revealed global good activity against the K1-multi-resistant Plasmodium falciparum strain, especially with hit compound 5 (IC(50)=0.9 μM), in comparison with chloroquine and doxycycline chosen as reference-drugs. Both the in vitro cytotoxicity study which was conducted on the human HepG2 cell line and the in vitro antitoxoplasmic screening against Toxoplasma gondii indicate that this series presents an interesting selective antiplasmodial profile. Structure-activity- and toxicity relationships highlight that the trichloromethyl group plays a key role in the antiplasmodial activity and also show that the modulation of the thiophenol moiety influences the toxicity/activity ratio.     

In vitro antiplasmodial investigation of medicinal plants from El Salvador

In vitro antiplasmodial activities of extracts from Albizia saman, Fabaceae, Calea tenuifolia (C. zacatechichi), Asteraceae, Hymenaea courbaril, Fabaceae, Jatropha curcas, Euphorbiaceae, Momordica charantia, Cucurbitaceae, and Moringa oleifera, Moringaceae were evaluated. From the lipophilic extract of C tenuifolia five active flavones were obtained. 4',5-Dihydroxy-7-methoxyflavone [genkwanin] and 5-hydroxy-4',7-dimethoxyflavone [apigenin 4',7-dimethylether] exhibited the strongest antiplasmodial activity against a chloroquine-sensitive strain (poW) and a chloroquine-resistant strain (Dd2) of Plasmodium falciparum [IC50 values: 17.1-28.5 microM). Furthermore octadeca-9,12-dienoic acid [linoleic acid] [IC50] values of 21.8 microM (poW) and 31.1 microM (Dd2)] and octadeca-9,12,15-trienoic acid (alpha-linolenic acid) were isolated.     

Turkish freshwater and marine macrophyte extracts show in vitro antiprotozoal activity and inhibit FabI, a key enzyme of Plasmodium falciparum fatty acid biosynthesis.

The ethanolic extracts of a number of Turkish freshwater macrophytes (Potamogeton perfoliatus, Ranunculus tricophyllus and Cladophora glomerata) and marine macroalgae (Dictyota dichotoma, Halopteris scoparia, Posidonia oceanica, Scinaia furcellata, Sargassum natans and Ulva lactuca) were assayed for their in vitro antiprotozoal activity. Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum were used as test organisms. The cytotoxicity of the extracts was also assessed against primary rat skeletal myoblasts (L6 cells). Whereas none of the extracts were active against T. cruzi, all crude extracts displayed appreciable trypanocidal activity against T. brucei rhodesiense, with S. natans being the most active one (IC(50) 7.4microg/ml). Except for the marine alga H. scoparia, all extracts also possessed leishmanicidal potential. The best antileishmanial activity was exerted by U. lactuca and P. oceanica (IC(50)'s 5.9 and 8.0microg/ml, respectively). Five extracts that demonstrated inhibitory activity towards P. falciparum (IC(50)'s 18.1-48.8microg/ml) were simultaneously assayed against FabI, a crucial enzyme of the fatty acid system of P. falciparum, to find out whether FabI was their target. The extracts of C. glomerata and U. lactuca efficiently inhibited the FabI enzyme with IC(50) values of 1.0 and 4.0microg/ml, respectively. None of the extracts were cytotoxic towards mammalian L6 cells. This work reports for the first time antiprotozoal activity of some Turkish marine and freshwater algae, as well as a target-based antiplasmodial screening for the identification of P. falciparum FabI inhibitors from aquatic and marine macrophytes.     

Synthesis of a Microcystis aeruginosa predicted metabolite with antimalarial activity

The synthesis of a Microcystis aeruginosa predicted metabolite analog of aerucyclamide B was performed. This hexacyclopeptide was obtained from three heterocyclic building blocks by a convergent macrocycle-assembly methodology. The compound exhibited good in vitro antiplasmodial activity (IC(50): 0.18 μM, K1, cholorquine resistant strain).     

Studies on medicinal plants of Ivory Coast: investigation of Sida acuta for in vitro antiplasmodial activities and identification of an active constituent.

Sida acuta Burm. (Malvaceae) originating from Ivory Coast was selected after an ethnobotanical survey: traditional healers of malaria commonly used this plant for the treatment. Extracts were tested on two strains of Plasmodium falciparum: FcM29-Cameroon (chloroquine-resistant strain) and a Nigerian chloroquine-sensitive strain. Extracts were obtained by preparing decoction in water of the powdered plant, the technique used by most of the traditional healers. An ethanol extract was then made and tested. The IC50 values obtained for these extracts ranged from 3.9 to -5.4 microg/ml. Purification of this active fraction led to the identification of cryptolepine as the active antiplasmodial constituent of the plant.     

HPLC quantification of uncarine D and the anti-plasmodial activity of alkaloids from leaves of Mitragyna inermis (Willd.) O. Kuntze

An efficient system for the analysis of the total alkaloids extracted from leaves of Mitragyna inermis (Willd.) O. Kuntze (Rubiaceae) by HPLC using a reversed-phase column is described. The chromatographic conditions allowed the separation of indole and oxindole alkaloids in leaf extracts, and the quantification of uncarine D in samples collected in Burkina Faso and Mali. The HPLC method described was validated for its specificity, linearity and precision using an internal standard (naphthalene). The concentrations of uncarine D in various extracts were compared with their in vitro anti-plasmodial activity. The anti-proliferative activity on chloroquine-resistant strain (W2) of Plasmodium falciparum was not correlated with the concentration of uncarine D in leaves.     

Antiplasmodial benzophenones from the trunk latex of Moronobea coccinea (Clusiaceae)

In an effort to find antimalarial drugs, a systematic in vitro evaluation on a chloroquine-resistant strain of Plasmodium falciparum (FcB1) was undertaken on sixty plant extracts collected in French Guiana. The methanol extract obtained from the latex of Moronobea coccinea exhibited a strong antiplasmodial activity (95% at 10 μg/ml). The phytochemical investigation of this extract led to the isolation of eleven polycyclic polyprenylated acylphloroglucinols (PPAPs), from which eight showed potent antiplasmodial activity with IC50 ranged from 3.3 μM to 37.2 μM.     

An in vitro evaluation of human cytochrome P450 3A4 inhibition by selected commercial herbal extracts and tinctures.

Serial dilutions of 21 commercial ethanolic herbal extracts and tinctures, and 13 related pure plant compounds have been analyzed for their in vitro cytochrome P450 3A4 (CYP3A4) inhibitory capability via a fluorometric microtitre plate assay. Roughly 75% of the commercial products and 50% of the pure compounds showed significant inhibition of CYP3A4 metabolite formation. For each herbal product and pure compound exhibiting dose-dependency, the inhibition values were used to generate median inhibitory concentration (IC50) curves using linear regression. Among the commercial extracts, Hydrastis canadensis (goldenseal), Hypericum perforatum (St. John's wort), and Uncaria tomentosa (cat's claw) had the lowest IC50 values at < 1% full strength, followed by Echinacea angustifolia roots, Trifolium pratense (wild cherry), Matricaria chamomilla (chamomile), and Glycyrrhiza glabra (licorice), which had IC50 values ranging from 1%-2% of full strength. Dillapiol, hypericin, and naringenin had the lowest IC50 values among the pure plant compounds at < 0.5 mM; dillapiol was the most potent inhibitor at 23.3 times the concentration of the positive CYP3A4 inhibitor ketoconazole. Utilizing high-throughput screening methodologies for assessing CYP3A4 inhibition by natural products has important implications for predicting the likelihood of potential herbal-drug interactions, as well as determining candidates for further in-depth analyses.     

Synthesis and chloroquine-enhancing activity of Na-deacetyl-ferrocenoyl-strychnobrasiline

Several strychnobrasiline derivatives have been synthesized to overcome the lack of in vivo reversal activity of the parent compound. In the present study, N(a)-deacetyl-ferrocenoyl-strychnobrasiline was synthesized by condensing N(a)-deacetyl-strychnobrasiline with ferrocenic acid previously treated with oxalyl chloride. While the in vitro antiplasmodial activity of the test compound (IC(50)=4.83 microg/mL) was increased 15-fold compared to that of strychnobrasiline, and the in vitro enhancing activity was found to be similar to that of the parent compound, the compound was devoid of any in vivo potentiating effect, and an antagonistic effect was even observed at higher doses. Based on the overall results on the hemisynthesis of strychnobrasiline derivatives for better reversal activity, this strategy has appeared to be of little value for useful drugs.     

Tumor promoting diterpenes from Euphorbia leuconeura L.

Diterpene esters of the phorbol and ingenol types are known to be highly active tumor promoting agents that typically occur in members of the Euphorbiaceae. In the present work, Euphorbia leuconeura, a rare indoor plant, is analyzed for its tumor promoting potential. Latex as well as total leaf extracts exhibited Epstein-Barr-virus (EBV) inducing activity comparable to 12-O-tetradecanoyl-phorbol-13-O-acetate, a well known tumor promoter. The activity of individual fractions correlated with their ingenol ester content. Three ingenol esters with EBV inducing activity could be isolated and identified. They belong to the milliamine type of diterpene esters that contain aromatic peptidyl groups. Two of them (milliamines L and M) are already known from E. milii. The third compound is identified as an isomer of milliamine F with a novel 3,20-diester arrangement. The data show a close relationship between E. leuconeura and the more popular indoor plant E. milii whose latex is also used as a powerful molluscicide.