Chloroquine-resistant Strains Of Plasmodium Falciparum Research Articles

In Vitro Antiplasmodial Activity of an Azadirachta indica Cell Culture Extract

Azadirachta indica A. Juss (neem tree) is used in Nigeria and India to control malaria. Due to the difficulty to obtain secondary metabolites from this plant, this study aimed to evaluate the in vitro antiplasmodial activity of extracts and fractions of A. indica cell culture on chloroquine-resistant Plasmodium falciparum (FCR3) strains. A. indica cell culture was carried on in stirred tank bioreactor. Biomass from this process was extracted with ethanol and subsequently fractionated with different solvents. Ethanolic extract and fractions obtained were tested in bioassays on chloroquine-resistant Plasmodium falciparum (FCR3) strains. Chloroquine was used as positive control. Finally, hexane fraction was analyzed by ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry, to tentatively identify some compounds that might be involved in antiplasmodial activity. The extract showed promising activity with a half-maximal (50%) inhibitory concentration (IC50) of 6.14 μg ml−1, which decreased with the time (IC50: 33.64 µg ml−1 for at > 18 months). Some extract fractions showed impressive activity against P. falciparum with IC50 values of 13.66 and 9.80 µg ml−1 for the hexane and dichloromethane fractions at > 18 months, which was higher than that of the crude extract during the same time frame. Also, 16 compounds were partially identified in hexane fraction. This is the first study reporting in vitro antiplasmodial activity of extracts of A. indica obtained by biotechnology way. The in vitro antiplasmodial activity of the A. indica cell culture ethanolic extract was demonstrated, and this extract could be a potential future alternative for treating and controlling malaria.

Antiplasmodial Alkaloids from the Australian Bryozoan Amathia lamourouxi.

An extract from the bryozoan Amathia lamourouxi with antiplasmodial activity was identified through high-throughput screening of an Australian marine invertebrate extract library against Plasmodium falciparum. Chemical investigation of A. lamourouxi resulted in the isolation of six new brominated alkaloids, convolutamines K and L (1 and 2), volutamides F-H (3-5), and 2,5-dibromo-1-methyl-1H-indole-3-carbaldehyde (6). Three of the compounds (2-4) displayed moderate to potent antiplasmodial activity against both the chloroquine-sensitive (3D7) and chloroquine-resistant (Dd2) parasite strains of Plasmodium falciparum with an IC50 range of 0.57-1.7 μM and a high selectivity index against a human cell line (HEK293).

Cytotoxic and Anti-Plasmodial Activities of Stephania dielsiana Y.C. Wu Extracts and the Isolated Compounds.

Natural products remain a viable source of novel therapeutics, and as detection and extraction techniques improve, we can identify more molecules from a broader set of plant tissues. The aim of this study was an investigation of the cytotoxic and anti-plasmodial activities of the methanol extract from Stephania dielsiana Y.C. Wu leaves and its isolated compounds. Our study led to the isolation of seven alkaloids, among which oxostephanine (1) is the most active against several cancer cell lines including HeLa, MDA-MB231, MDA-MB-468, MCF-7, and non-cancer cell lines, such as 184B5 and MCF10A, with IC50 values ranging from 1.66 to 4.35 μM. Morever, oxostephanine (1) is on average two-fold more active against cancer cells than stephanine (3), having a similar chemical structure. Cells treated with oxostephanine (1) are arrested at G2/M cell cycle, followed by the formation of aneuploidy and apoptotic cell death. The G2/M arrest appears to be due, at least in part, to the inactivation of Aurora kinases, which is implicated in the onset and progression of many forms of human cancer. An in-silico molecular modeling study suggests that oxostephanine (1) binds to the ATP binding pocket of Aurora kinases to inactivate their activities. Unlike oxostephanine (1), thailandine (2) is highly effective against only the triple-negative MDA-MB-468 breast cancer cells. However, it showed excellent selectivity against the cancer cell line when compared to its effects on non-cancer cells. Furthermore, thailandine (2) showed excellent anti-plasmodial activity against both chloroquine-susceptible 3D7 and chloroquine-resistant W2 Plasmodium falciparum strains. The structure–activity relationship of isolated compound was also discussed in this study. The results of this study support the traditional use of Stephania dielsiana Y.C. Wu and the lead molecules identified can be further optimized for the development of highly effective and safe anti-cancer and anti-plasmodial drugs.

Building on Surface-Active Ionic Liquids for the Rescuing of the Antimalarial Drug Chloroquine.

Ionic liquids derived from classical antimalarials are emerging as a new approach towards the cost-effective rescuing of those drugs. Herein, we disclose novel surface-active ionic liquids derived from chloroquine and natural fatty acids whose antimalarial activity in vitro was found to be superior to that of the parent drug. The most potent ionic liquid was the laurate salt of chloroquine, which presented IC50 values of 4 and 110 nM against a chloroquine-sensitive and a chloroquine-resistant strain of Plasmodium falciparum, respectively, corresponding to an 11- and 6-fold increase in potency as compared to the reference chloroquine bisphosphate salt against the same strains. This unprecedented report opens new perspectives in both the fields of malaria chemotherapy and of surface-active ionic liquids derived from active pharmaceutical ingredients.

Ceramides and other bioactive compounds from Celtis tessmannii Rendle

Two previously undescribed ceramides, named celtisamide A ( 1 ) and B ( 2 ), along with 16 known compounds ( 3 - 18 ), were isolated both from the stem bark and roots of Celtis tessmannii Rendle. The isolated compounds were assessed in vitro for their DPPH radical scavenging, antiplasmodial activity as well as their urease and lipoxygenase inhibitory properties. In addition, fractions and extracts were also evaluated for antiplasmodial and cytotoxicity activities against HEK293T. Cis -1- O -methylinositol ( 17 ) (IC 50 = 14.3 µ M) was the most potent inhibitor of urease, while succinic acid ( 18 ) (IC 50 = 12.9 µ M) exhibited the best inhibition against lipoxygenase. Compound 18 (IC 50 = 9.5 µ M) showed the best DPPH radical scavenging activity. Extracts and fractions exhibited varying degree of antiplasmodial potency with IC 50 values ranging from 2.42-100.00 µ g/mL, while betulinic acid ( 7 ) showed potency with IC 50 values ranging from 1.87-2.34 µ g/mL against Chloroquine-sensitive ( Pf 3D7), and Chloroquine-resistant ( Pf Dd2 and Pf INDO) strains of Plasmodium falciparum .

Antiparasitic Constituents of Beilschmiedia louisii and Beilschmiedia obscura and Some Semisynthetic Derivatives (Lauraceae).

The MeOH/CH2Cl2 (1:1) extracts of the roots and leaves of Beilschmiedia louisii and B. obscura showed potent antitrypanosomal activity during preliminary screening on Trypanosoma brucei brucei. Phytochemical investigation of these extracts led to the isolation of a mixture of two new endiandric acid derivatives beilschmiedol B (1) and beilschmiedol C (2), and one new phenylalkene obscurene A (3) together with twelve known compounds (4–15). In addition, four new derivatives (11a–11d) were synthesized from compound 11. Their structures were elucidated based on their NMR and MS data. Compounds 5, 6, and 7 were isolated for the first time from the Beilschmiedia genus. Additionally, the NMR data of compound 4 are given here for the first time. The isolates were evaluated for their antitrypanosomal and antimalarial activities against Tb brucei and the Plasmodium falciparum chloroquine-resistant strain Pf3D7 in vitro, respectively. From the tested compounds, the mixture of new compounds 1 and 2 exhibited the most potent antitrypanosomal activity in vitro with IC50 value of 4.91 μM.

Design, Synthesis, Structure‐Activity Relationship and Docking Studies of Novel Functionalized Arylvinyl‐1,2,4‐Trioxanes as Potent Antiplasmodial as well as Anticancer Agents

A novel series of synthetic functionalized arylvinyl-1,2,4-trioxanes (8 a-p) has been prepared and assessed for their in vitro antiplasmodial activity against the chloroquine-resistant Pf INDO strain of Plasmodium falciparum by using a SYBR green-I fluorescence assay. Compounds 8 g (IC50 =0.051 μM; SI=589.41) and 8 m (IC50 =0.059 μM; SI=55.93) showed 11-fold and >9-fold more potent antiplasmodial activity, respectively, as compared to chloroquine (IC50 =0.546 μM; SI=36.63). Different in silico docking studies performed on many target proteins revealed that the most active arylvinyl-1,2,4-trioxanes (8 g and 8 m) showed dihydrofolate reductase (DHFR) binding affinities on a par with those of chloroquine and artesunate. The in vitro cytotoxic potentials of 8 a-p were also evaluated against human lung (A549) and liver (HepG2) cancer cell lines along with immortalized normal lung (BEAS-2B) and liver (LO2) cell lines. Following screening, five derivatives viz. 8 a, 8 h, 8 l, 8 m and 8 o (IC50 =1.65-31.7 μM; SI=1.08-10.96) were found to show potent cytotoxic activity against (A549) lung cancer cell lines, with selectivity superior to that of the reference compounds artemisinin (IC50 =100 μM), chloroquine (IC50 =100 μM) and artesunic acid (IC50 =9.85 μM; SI=0.76). In fact, the most active 4-naphthyl-substituted analogue 8 l (IC50 =1.65 μM; SI >10) exhibited >60 times more cytotoxicity than the standard reference, artemisinin, against A549 lung cancer cell lines. In silico docking studies of the most active anticancer compounds, 8 l and 8 m, against EGFR were found to validate the wet lab results. In summary, a new series of functionalized aryl-vinyl-1,2,4-trioxanes (8 a-p) has been shown to display dual potency as promising antiplasmodial and anticancer agents.

In Vitro Antiplasmodial Activity and Cytotoxicity of Active Subfractions of Harmsiopanax aculeatus Leaves

Harmsiopanax aculeatus leaves, a medicinal plant with locally named kapur , have been used traditionally to treat malaria in Maluku, Indonesia. However, the scientific information of this plant is still limited. In our previous study, the methanol extract of this plant leaves have been proven to possess in vitro antiplasmodial activity. This study was conducted to evaluate in vitro antiplasmodial activity and cytotoxicity of subfractions of the plant leaves. Fractionation was performed using a column chromatography with Sephadex LH-20 as the stationary phase and methanol as the mobile phase. The subfractions obtained were then tested for in vitro antiplasmodial activity on a chloroquine-resistant FCR3 strain of Plasmodium falciparum using a visual method. Cytotoxicity was evaluated by using MTT assay. The in vitro antiplasmodial activity and cytotoxicity were expressed as IC 50 , calculated using probit analysis with SPSS 16 for windows. The results showed that the four subfractions tested have a high antiplasmodial activity with IC 50 values of 0.09; 0.18; 0.01; and 0.77 µg.mL -1 , respectively. In addition, these subfractions had IC 50 values of >400 µg.mL -1 against Vero cells indicating that they were non-toxic. In conclusion, the subfractions of H. aculeatus leaves are very active and selective against P. falciparum . Further study will be conducted to isolate the active compounds.

In vitro Multistage Malaria Transmission Blocking Activity of Selected Malaria Box Compounds.

PurposeContinuous efforts into the discovery and development of new antimalarials are required to face the emerging resistance of the parasite to available treatments. Thus, new effective drugs, ideally able to inhibit the Plasmodium life-cycle stages that cause the disease as well as those responsible for its transmission, are needed. Eight compounds from the Medicines for Malaria Venture (MMV) Malaria Box, potentially interfering with the parasite polyamine biosynthesis were selected and assessed in vitro for activity against malaria transmissible stages, namely mature gametocytes and early sporogonic stages.MethodsCompound activity against asexual blood stages of chloroquine-sensitive 3D7 and chloroquine-resistant W2 strains of Plasmodium falciparum was tested measuring the parasite lactate dehydrogenase activity. The gametocytocidal effect was determined against the P. falciparum 3D7elo1-pfs16-CBG99 strain with a luminescent method. The murine P. berghei CTRP.GFP strain was employed to assess compounds activities against early sporogonic stage development in an in vitro assay simulating mosquito midgut conditions.ResultsAmong the eight tested molecules, MMV000642, MMV000662 and MMV006429, containing a 1,2,3,4-tetrahydroisoquinoline-4-carboxamide chemical skeleton substituted at N-2, C-3 and C-4, displayed multi-stage activity. Activity against asexual blood stages of both strains was confirmed with values of IC50 (50% inhibitory concentration) in the range of 0.07–0.13 µM. They were also active against mature stage V gametocytes with IC50 values below 5 µM (range: 3.43–4.42 µM). These molecules exhibited moderate effects on early sporogonic stage development, displaying IC50 values between 20 and 40 µM.ConclusionGiven the multi-stage, transmission-blocking profiles of MMV000642, MMV000662, MMV006429, and their chemical characteristics, these compounds can be considered worthy for further optimisation toward a TCP5 or TCP6 target product profile proposed by MMV for transmission-blocking antimalarials.

Clonocoprogens A, B and C, new antimalarial coprogens from the Okinawan fungus Clonostachys compactiuscula FKR-0021.

Three new antimalarial compounds, clonocoprogens A, B, and C, were isolated from the static culture of an Okinawan fungus, Clonostachys compactiuscula FKR-0021. These compounds were new analogs of N14-palmitoylcoprogen, reported as a siderophore. They showed moderate antimalarial activity against chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum strains, with IC50 values ranging from 1.7 to 9.9 µM.

In vitro antiplasmodial and cytotoxicity activities of crude extracts and major compounds from Goniothalamus lanceolatus

Ethnopharmacological relevanceMalaria, a devastating infectious disease which was initially recognized as episodic fever, is caused by parasitic protozoan of the genus Plasmodium. Medicinal plants with ethnobotanical information to treat fever and/or malaria has been the key element in identifying potential plant candidates for antimalarial screening. Goniothalamus lanceolatus Miq. (Annonaceae) is used as a folk remedy, particularly to treat fever and skin diseases. Aim of the studyIn this context, supported with previous preliminary data of its antiplasmodial activity, this study was undertaken to determine the in vitro antiplasmodial and cytotoxicity activities of G. lanceolatus crude extracts and its major compounds. Materials and methodsThe in vitro antiplasmodial activity was determined by parasite lactate dehydrogenase (pLDH) assay on chloroquine-sensitive (3D7) and chloroquine-resistant (K1) strains of Plasmodium falciparum. The cytotoxicity activity was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay on hepatocellular carcinoma (HepG2) and normal liver (WRL-68) cell lines. ResultsThe root methanol extract possessed potent antiplasmodial activity against both P. falciparum 3D7 and K1 strains (IC50 = 2.7 μg/ml, SI = 140; IC50 = 1.7 μg/ml, SI = 236). Apart from the DCM extract of stem bark and root that were found to be inactive (IC50 > 50 μg/ml) against 3D7 strain, all other tested crude extracts exhibited promising (5< IC50 < 15 μg/ml) to moderate (15< IC50 < 50 μg/ml) antiplasmodial activity against both strain. Additionally, only compound C (Parvistone D) exerted promising antiplasmodial activity against 3D7 strain (IC50 = 7.5 μM, SI = 51) whereas compound A, B and D showed moderate antiplasmodial activity against the same strain (20 < IC50 < 100 μM). Interestingly, when tested on K1 strain, compound A, C and D exhibited promising antiplasmodial activity (2 < IC50 < 20 μM) while compound B exhibited moderate activity (IC50 = 26.9 μM). Cytotoxicity study showed that all tested crude extracts and compounds were non-toxic on WRL-68 and HepG2 cell lines (CC50 > 30 µg/ml, CC50 > 10 µM, respectively), except for the hexane and DCM extracts of root, which exerted mild cytotoxicity on HepG2 cell line (IC50 < 30 μg/ml). ConclusionsThis study suggests that the root methanol extract and compound C (Parvistone D) obtained from G. lanceolatus are highly potential for exploitation as source of antimalarial agents. Parvistone D is identified as one of the bioactive styryl lactones found in the plant extract. It is also noteworthy, that the extract and compound were more active against chloroquine-resistant (K1) strain of P. falciparum. Further studies are being carried out to assess their toxicity profile and antimalarial efficacy in animal model.

Design and synthesis of novel ferrocene-quinoline conjugates and evaluation of their electrochemical and antiplasmodium properties

The tropical disease malaria is responsible for more than 400,000 deaths annually, especially in Southeast Asia and Africa. Although the number of malaria cases is declining, there still is an urgent need for novel antimalarial agents. The emergence of hybrid antimalarial agents and the precedence set by the antimalarial drug ferroquine (FQ) prompted us to design new ferrocene-containing quinoline structures. Herein, we report the efficient synthesis of three different series of ferrocene-quinoline conjugates and a class of ferrocene-containing heterotricycles in good to high yields. For all twenty novel ferrocenyl derivatives, electrochemical properties were investigated using cyclic voltammetry and antiplasmodium evaluation against a chloroquine-susceptible NF54 strain of the human malaria parasite Plasmodium falciparum was conducted, pointing to three compounds showing submicromolar potency. Subsequently, cytotoxicity assays against a Chinese Hamster Ovarian cell line and evaluation against a chloroquine-resistant strain of Plasmodium falciparum for these three compounds revealed selective and promising antiplasmodium activity.

Design, synthesis, heme binding and density functional theory studies of isoindoline-dione-4-aminoquinolines as potential antiplasmodials.

Aim:WHO Malaria report 2017 estimated 216 million cases of malaria and 445,000 deaths worldwide, with 91% of deaths affecting the African region.Results/methodology:Microwave promoted the synthesis of cycloalkyl amine substituted isoindoline-1,3-dione-4-aminoquinolines was urbanized for evaluating their antiplasmodial activities. Compound with the optimum combination of propyl chain length and hydroxyethyl piperazine proved to be the most potent among the synthesized scaffolds against chloroquine-resistant W2 strain of Plasmodium falciparum with an IC50 value of 0.006 μM. Heme-binding along with density functional theory studies were further carried out in order to delineate the mechanism of action of the most active compound.Conclusion:The synthesized scaffold can act as a therapeutic template for further synthetic modifications toward the search for a new antimalarial agent.

Terminalia albida treatment improves survival in experimental cerebral malaria through reactive oxygen species scavenging and anti-inflammatory properties

BackgroundThe development of Plasmodium resistance to the last effective anti-malarial drugs necessitates the urgent development of new anti-malarial therapeutic strategies. To this end, plants are an important source of new molecules. The objective of this study was to evaluate the anti-malarial effects of Terminalia albida, a plant used in Guinean traditional medicine, as well as its anti-inflammatory and antioxidant properties, which may be useful in treating cases of severe malaria.MethodsIn vitro antiplasmodial activity was evaluated on a chloroquine-resistant strain of Plasmodium falciparum (K-1). In vivo efficacy of the plant extract was measured in the experimental cerebral malaria model based on Plasmodium berghei (strain ANKA) infection. Mice brains were harvested on Day 7–8 post-infection, and T cells recruitment to the brain, expression levels of pro- and anti-inflammatory markers were measured by flow cytometry, RT-qPCR and ELISA. Non-malarial in vitro models of inflammation and oxidative response were used to confirm Terminalia albida effects. Constituents of Terminalia albida extract were characterized by ultra‐high performance liquid chromatography coupled with high resolution mass spectrometry. Top ranked compounds were putatively identified using plant databases and in silico fragmentation patterns.ResultsIn vitro antiplasmodial activity of Terminalia albida was confirmed with an IC50 of 1.5 μg/mL. In vivo, Terminalia albida treatment greatly increased survival rates in P. berghei-infected mice. Treated mice were all alive until Day 12, and the survival rate was 50% on Day 20. Terminalia albida treatment also significantly decreased parasitaemia by 100% on Day 4 and 89% on Day 7 post-infection. In vivo anti-malarial activity was related to anti-inflammatory properties, as Terminalia albida treatment decreased T lymphocyte recruitment and expression of pro-inflammatory markers in brains of treated mice. These properties were confirmed in vitro in the non-malarial model. In vitro, Terminalia albida also demonstrated a remarkable dose-dependent neutralization activity of reactive oxygen species. Twelve compounds were putatively identified in Terminalia albida stem bark. Among them, several molecules already identified may be responsible for the different biological activities observed, especially tannins and triterpenoids.ConclusionThe traditional use of Terminalia albida in the treatment of malaria was validated through the combination of in vitro and in vivo studies.

Antiplasmodial activity of triterpenes isolated from the methanolic leaf extract of Combretum racemosum P. Beauv.

Combretum racemosum showed activity in previous ethnopharmacological investigations of some Combretum species used in malaria treatment in parts of West Africa. This study aimed at confirming the antimalarial potential of this plant by an activity-guided isolation of its active principles. A crude methanolic leaf extract of Combretum racemosum and fractions thereof obtained by partition with chloroform and n-butanol were investigated for antiplasmodial activity against chloroquine-sensitive (D10) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Repeated chromatographic separations were conducted on the chloroform fraction to isolate bioactive compounds for further tests on antiplasmodial activity. The characterization of the isolated substances was performed by applying NMR- and MS-techniques (ESI-MS, HR-ESIMS, 1D and 2D NMR). The chloroform fraction (D10: IC50 = 33.8 ± 1.5 μg/mL and W2: IC50 = 27.8 ± 2.9 μg/mL) exhibited better antiplasmodial activity than the n-butanol fraction (D10: IC50 = 78.1 ± 7.3 μg/mL and W2: IC50 = 78 ± 15 μg/mL) as well as the methanolic raw extract (D10: IC50 = 64.2 ± 2.7 μg/mL and W2: IC50 = 65.8 ± 14.9 μg/mL). Thus, the focus of the phytochemical investigation was laid on the chloroform fraction, which led to the identification of four ursane-type (19α-hydroxyasiatic acid (1), 6β,23-dihydroxytormentic acid (4), madecassic acid (8), nigaichigoside F1 (10)) and four oleanane-type (arjungenin (2), combregenin (5), terminolic acid (7), arjunglucoside I (11)) triterpenes, as well as abscisic acid (9). Compounds 1 and 2, 4 and 5, 7 and 8 as well as 10 and 11 were isolated as isomeric mixtures in fractions CR-A, CR-C, CR-E and CR-H, respectively. All isolated compounds and mixtures exhibited moderate to low activity, with madecassic acid being most active (D10: IC50 = 28 ± 12 μg/mL and W2: IC50 = 17.2 ± 4.3 μg/mL). This paper reports for the first time antiplasmodial principles from C. racemosum and thereby gives reason to the traditional use of the plant.

Isolation and characterization of antiplasmodial constituents from the marine sponge Coscinoderma sp.

Six known compounds, namely two halisulfates 1 and 2 and four epidioxy sterols 3-6, were isolated from the marine sponge Coscinoderma sp. The structures of these compounds were confirmed by nuclear magnetic resonance (1H and 13C NMR) spectroscopy, and their antiplasmodial activities were determined against the chloroquine-resistant Dd2 strain of Plasmodium falciparum. The epidioxy steroids 3-6 all showed moderate to weak antiplasmodial activity, with IC50 values of 2.7 μM for (24S)-5α,8α-epidioxy-24-methylcholesta-6-en-3β-ol (3), 11.6 μM for 5α,8α-epidioxycholesta-6,24(28)-dien-3β-o1 (4), 2.33 μM for 5α,8α-epidioxy-24-methylcholesta-6,9(11)-24(28)-trien-3β-ol (5), and between 12 and 24 μM for 5α,8α-epidioxycholesta-6-en-3β-ol (6). In contrast, halisulfate 2 (1) was inactive, and halisulfate 1 (2) had an of IC50 value of about 24 μM.

Anti-plasmodial Effects of Zanthoxylum zanthoxyloides.

Zanthoxylum zanthoxyloides, syn. Fagara zanthoxyloides, is a tree growing in West Africa and is used in traditional medicine against a variety of diseases, including malaria. In the work reported here, root bark and stem bark extracts of this tree, as well as compounds isolated from the extracts, have been investigated for activity in vitro against chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. In addition, toxicity against nauplii of the brine shrimp Artemia salina has been studied. Dichloromethane extracts of the root bark and stem bark, and a methanol extract of the stem bark, showed anti-parasitic activity towards chloroquine-sensitive as well as chloroquine-resistant P. falciparum, with IC50 values between 1 and 10 µg/mL. Among the isolated compounds, bis-dihydrochelerythrinyl ether, buesgenine, chelerythrine, γ-fagarine, skimmianine, and pellitorine were the most active, with IC50 values of less than 5 µg/mL. The dichloromethane extracts were toxic to brine shrimp nauplii, with LC50 values of less than 1 µg/mL. Methanol extracts were much less toxic (LC50 between 50 and 100 µg/mL). Among the isolated substances, bis-dihydrochelethrinyl ether was the most toxic (LC50 ca. 2 µg/mL).

Antiplasmodial Activity and In Vivo Bio-Distribution of Chloroquine Molecules Released with a 4-(4-Ethynylphenyl)-Triazole Moiety from Organometallo-Cobalamins

We have explored the possibility of using organometallic derivatives of cobalamin as a scaffold for the delivery of the same antimalarial drug to both erythro- and hepatocytes. This hybrid molecule approach, intended as a possible tool for the development of multi-stage antimalarial agents, pivots on the preparation of azide-functionalized drugs which, after coupling to the vitamin, are released with a 4-(4-ethynylphenyl)-triazole functionality. Three chloroquine and one imidazolopiperazine derivative (based on the KAF156 structure) were selected as model drugs. One hybrid chloroquine conjugate was extensively studied via fluorescent labelling for in vitro and in vivo bio-distribution studies and gave proof-of-concept for the design. It showed no toxicity in vivo (zebrafish model) as well as no hepatotoxicity, no cardiotoxicity or developmental toxicity of the embryos. All 4-(4-ethynylphenyl)-triazole derivatives of chloroquine were equally active against chloroquine-resistant (CQR) and chloroquine-sensitive (CQS) Plasmodium falciparum strains.

Bridged bicyclic 2,3-dioxabicyclo[3.3.1]nonanes as antiplasmodial agents: Synthesis, structure-activity relationships and studies on their biomimetic reaction with Fe(II)

Despite recent advancements in its control, malaria is still a deadly parasitic disease killing millions of people each year. Progresses in combating the infection have been made by using the so-called artemisinin combination therapies (ACTs). Natural and synthetic peroxides are an important class of antimalarials. Here we describe a new series of peroxides synthesized through a new elaboration of the scaffold of bicyclic-fused/bridged synthetic endoperoxides previously developed by us. These peroxides are produced by a straightforward synthetic protocol and are characterized by submicromolar potency when tested against both chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum strains. To investigate their mode of action, the biomimetic reaction of the representative compound 6w with Fe(II) was studied by EPR and the reaction products were characterized by NMR. Rationalization of the observed structure-activity relationship studies was performed by molecular docking. Taken together, our data robustly support the hypothesized mode of activation of peroxides 6a-cc and led to the definition of the key structural requirements responsible for the antiplasmodial potency. These data will pave the way in future to the rational design of novel optimized antimalarials suitable for in vivo investigation.

Microwave-assisted, rapid synthesis of 2-vinylquinolines and evaluation of their antimalarial activity

A rapid and efficient synthesis of 2-vinylquinolines via trifluoromethanesulfonamide-mediated olefination of 2-methylquinoline and aldehyde under microwave irradiation is reported. Biological evaluation of these scaffolds demonstrates that 2-vinylquinolines 3x-3z possess excellent antimalarial activities against chloroquine-resistant Dd2 strain of Plasmodium falciparum (IC50 < 100 nM).