N,N-Bis(trifluoromethylquinolin-4-yl)diamino alkanes: synthesis and antimalarial activity

A series of N,N-bis(trifluoromethylquinolin-4-yl)- and N,N-bis[2,8-bis(trifluoromethyl)quinolin-4-yl] diamino alkane and piperazine derivatives were synthesised by employing a simple and rapid displacement reaction of the 4-chloro group on the 2-trifluoromethyl- and 2,8-bis(trifluoromethyl)-quinoline by diaminoalkane or piperazine groups. Results of in vitro antimalarial activity evaluations of these compounds against the chloroquine-sensitive (D10) and chloroquine-resistant (K1) strains of Plasmodium falciparum indicate that compounds with trifluoromethyl groups in both the 2 and 8 positions coupled with diaminoalkyl bridging chains of 2 to 6 carbon atoms exhibit a slightly higher activity than compound with only a trifluoromethyl group at position 2, and those with a piperazine bridge. These compounds exhibit higher activity in the chloroquine-resistant than in the chloroquine-sensitive strains of the Plasmodium. Comparative studies indicate that the compounds are more selective in their cytotoxicity against the parasite cells. Except for compounds containing a piperazine bridge, this new series of compounds interact with ferriprotoporphyrin IX to more or less the same extent.     

Synthesis and antimalarial activity of novel side chain modified antimalarial agents derived from 4-aminoquinoline

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (de-alklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4-aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4-aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.     

Antimalarial activity of new gossypol derivatives

Gossypol, a disesquiterpene extracted from cotton seeds, is known to inhibit strongly the Plasmodium falciparum lactate dehydrogenase, but its high toxicity has stopped any antimalarial drug development. A series of Schiff's bases was synthesized from gossypol by modification of the aldehyde groups responsible for its toxicity. A total of 13 compounds showing low cytotoxicity were then selected and were compared with gossypol for activity against 2 chloroquine-resistant strains of P. falciparum (PFB, FCB1). These in vitro activities were evaluated using an isotope-based drug-susceptibility semiautomated microdilution test followed by determination of IC₅₀ values (50% inhibitory concentration). In all, 12 of the 13 compounds tested were active; 3 of them displayed antimalarial activity comparable with that of gossypol itself. Received: 27 November 1999 / Accepted: 28 January 2000     

In vitro antimalarial activity of extracts of Albizia gummifera,Aspilia mossambicensis,Melia azedarach and Azadirachta indica against Plasmodium falciparum

Since chemotherapy is presently the primary strategy of malaria control in the world, and some malaria parasites are developing resistance to the commonly used antimalarial drugs, new antimalarial compounds are required. Therefore, it is important to test antimalarial activities of medicinal plant extracts which most herbalists claim to cure malaria. We evaluated the antimalarial activities of extracts of Albizia gummiffera, Aspilia mossambicensis, Melia azedar and Azadirahchta indica against laboratory adapted isolates of Plasmodium falciparum using an in vitro radioisotopic uptake technique. Chloroquine was used as a reference antimalarial drug. Al. gummifera had the highest antimalarial activity (mean fifty percent inhibitory concentration {IC(50)S} in ug/ml of test culture =3.5 +1.6SD, n=3) followed by As. mossambicensis (mean IC(50)=29.3+11.8SD, n=4) and Me. Azedarach (mean IC(50) =299.7+202.0SD, n=4). And lastly Az. Indica (mean IC(50)=349.9+213.1 SD, n=4). The antimalarial activities of the reference drug, chloroquine, was far much higher (mean IC(50)=0.065+0.057SD, n=)4). These findings show that Al. gummifera and As. mossambicensis plant extracts have potent antimalarial compounds. Phytochemical analyses should be done on these two plants to isolate the compound(s) containing he active principles(s).     

Synthesis and biological evaluation of 2-aroyl-4-phenyl-5-hydroxybenzofurans as a new class of antitubulin agents

Microtubules are among the most successful targets for development of compounds useful for anticancer therapy. Continuing our project to develop new small molecule antitumor agents, two new series of derivatives based on the 2-aroyl-4-phenylbenzofuran molecular skeleton were synthesized and evaluated for antiproliferative activity, inhibition of tubulin polymerization and cell cycle effects. SAR were elucidated with various substitutions on the benzoyl moiety at the 2-position of the benzofuran ring. The most promising compound in this series, the (5-hydroxy-4-phenylbenzofuran-2-yl)(4-methoxyphenyl)methanone derivative (3d), has significant growth inhibitory activity in the submicromolar range against the Molt4, CEM and HeLa cancer cell lines and interacts with tubulin by binding to the colchicine site. Exposure to 3d led to the arrest of K562 cells in the G2-M phase of the cell cycle and to the induction of apoptosis.     

The Antimalarial Potential of Medicinal Plants Used for the Treatment of Malaria in Cameroonian Folk Medicine

Malaria remains one of the leading public health problems in Cameroon as in other parts of Sub-Saharan Africa. In the past decades, this situation has been aggravated by the increasing spread of drug-resistant Plasmodium falciparum strains. New antimalarial drug leads are therefore urgently needed. Traditional healers have long used plants to prevent or cure infections. This article reviews the current status of botanical screening efforts in Cameroon as well as experimental studies done on antimalarial plants. Data collected from 54 references from various research groups in the literature up to June 2007 shows that 217 different species have been cited for their use as antimalarials in folk medicine in Cameroon. About a hundred phytochemicals have been isolated from 26 species some among which are potential leads for development of new antiamalarials. Crude extracts and or essential oils prepared from 54 other species showed a wide range of activity on Plasmodium spp. Moreover, some 137 plants from 48 families that are employed by traditional healers remain uninvestigated for their presumed antimalarial properties. The present study shows that Cameroonian flora represents a high potential for new antimalarial compounds. Further ethnobotanical surveys and laboratory investigations are needed to fully exploit the potential of the identified species in the control of malaria.     

Proteome analysis of new antimalarial endoperoxide against Plasmodium falciparum

N-89, a new antimalarial endoperoxide, was selected as a promising antimalarial compound showing high activity and selectivity. To study the mechanism of N-89 action, N-89 resistant strain (NRC10) was obtained by intermittent drug pressure. NRC10 had a tenfold increase in the EC₅₀ value of N-89. No cross-resistance was obtained with other antimalarial compounds. Comparative proteome analysis of N-89 sensitive and NRC10 strains revealed over-expression of 12 spots and down-regulation of 14 spots in NRC10. Fifteen proteins were identified of Plasmodium falciparum origin. The identified proteins representing several functions, mainly related to the glycolytic pathway, and metabolism of protein and lipid. Our results suggest that identified proteins may be candidates of antimalarial endoperoxide targets.     

Antiplasmodial activity of alkaloid extracts from Pavetta crassipes (K. Schum) and Acanthospermum hispidum (DC), two plants used in traditional medicine in Burkina Faso

In the course of the search for new antimalarial compounds, a study of plants traditionally used against malaria in Burkina Faso was made. An ethnobotanical study permitted the identification of plants currently used by the traditional healers and herbalists. Two plants among them were selected for further study: Pavetta crassipes (K. Schum) and Acanthospermum hispidum (DC). Alkaloid extracts of these plants were tested in vitro against two reference clones of Plasmodium falciparum: the W2 chloroquine-resistant and the D6 chloroquine-sensitive strains. Significant inhibitory activity was observed with Pavetta crassipes (IC(50)=1.23 microg/ml) and A. hispidum (IC(50)=5.02 microg/ml). Antiplasmodial activity was also evaluated against six Plasmodium falciparum isolates from children between 4 and 10 years old. The IC(50) values for the alkaloid extracts were in the range 25-670 ng/ml. These results indicated that P. falciparum wild strains were more sensitive to the alkaloid extracts than strains maintained in continuous culture. Moreover, the alkaloid extracts exhibit good in vitro antimalarial activity and weak cytotoxicity against three human cell lines (THP1, normal melanocytes, HTB-66). Isolation and structural determination are now necessary in order to precisely determine the active compounds.     

Antimalarial drugs and their metabolites are potent Zika virus inhibitors

Studies aimed at repurposing existing drugs revealed that some antimalarial compounds possess anti-Zika virus (anti-ZIKV) activity. Here, we further tested 14 additional antimalarial drugs and their metabolites or analogs for anti-ZIKV activity using a phenotypic screening approach. We identified four compounds with varying anti-ZIKV activity, including a metabolite of amodiaquine termed desethylamodiaquine (DAQ) and N-desethylchloroquine (DECQ), a metabolite of chloroquine, which both exhibited low micromolar effective concentrations against three different ZIKV strains. Two other compounds termed dihydroartemisinin (DHA) and quinidine (QD) exhibited only partial inhibition of ZIKV replication. Characterization of the inhibitory mechanisms of DAQ and DECQ showed that both drugs target the entry step as well as postentry events of the viral replication cycle. These hits represent attractive starting points for future optimization of new anti-ZIKV drug candidates derived from antimalarial drugs and their analogs.     

Synthesis and anticancer activities of new Benzothiadiazinyl Hydrazinecarboxamides and Anilino[1,2,4]triazolo[1,5-b][1,2,4]thiadiazine 5,5-diones

Two series of compounds (5-14 and 15-23) based on the scaffolds of 2-(1,1-dioxido-4-phenyl-4Hbenzo[e][1,2,4]thiadiazin-3-yl)-N-(4-methoxyphenyl)hydrazinecarboxamide (5) and 2-((4-methoxyphenyl)amino)-10-phenyl-10H-benzo[e][1,2,4]triazolo[1,5-b][1,2,4]thiadiazine 5,5-dioxide (15) respectively, were designed and synthesized. These compounds were tested for anticancer activity against various cancer cell lines including lung, ovary, prostate, breast and colon cancers. They exhibited moderate to good inhibitory activity against the above cell lines and compound 9 was found to be the most active one from these two series. Further studies showed that cancer cell growth inhibition by compounds 22 and 23 could be in part due to the inhibition of tubulin polymerization, with the IC50 values of 4.70 and 5.25 μM, respectively.     

Antileishmanial and antimalarial chalcones: synthesis, efficacy and cytotoxicity of pyridinyl and naphthalenyl analogs

The antileishmanial and antimalarial activity of methoxy-substituted chalcones (1,3-diphenyl-2-propen-1-ones) is well established. The few analogs prepared to date where the 3-phenyl group is replaced by either a pyridine or naphthalene suggest these modifications are potency enhancing. To explore this hypothesis, sixteen 3-naphthalenyl-1-phenyl-2-prop-1-enones and ten 1-phenyl-3-pyridinyl-2-prop-1-enones were synthesized and their in vitro efficacies against Leishmania donovani and Plasmodium falciparum determined. One inhibitor with submicromolar efficacy against L. donovani was identified (IC50 = 0.95 microM), along with three other potent compounds (IC50 < 5 microM), all of which were 3-pyridin-2-yl derivatives. No inhibitors with submicromolar efficacy against P. falciparum were identified, though several potent compounds were found (IC50 < 5 microM). The cytotoxicity of the five most active L. donovani inhibitors was assessed. At best the IC50 against a primary kidney cell line was around two-fold higher than against L. donovani. Being more active than pentamidine, the 1-phenyl-3-pyridin-2-yl-2-propen-1-ones have potential for further development against leishmaniasis; however it will be essential in such a program to address not only efficacy but also their potential for toxicity.     

Design, synthesis and antimalarial activity of a new class of iron chelators

Iron is crucial for many biochemical reactions involved in the growth and multiplication of the malaria parasite Plasmodium falciparum. There are many reports indicating that the iron chelators have antimalarial activity in vitro, in vivo and in human studies. However, these compounds suffer from a number of serious problems such as limited membrane permeability, short half-life and require long subcutaneous infusions. To circumvent these drawbacks we have designed a new class of iron chelators, wherein EDTA is tethered to 4-aminoquinoline. Here 4-aminoquinoline scaffold is used as a carrier to penetrate biological membrane and facilitate targetting the compounds to acidic food vacuole of the parasite. This study describes the synthesis of novel iron chelators and their in vitro antimalarial activity against P. falciparum strain of NF-54. The calculated LogP values of these compounds suggest the importance of lipophilicity for the antimalarial activity. The EDTA esters are more active than the corresponding acids. The biophysical studies suggest that these compounds may inhibit the parasite growth by iron chelation mechanism.     

High-performance liquid chromatographic analysis of AQ4N, an alkylaminoanthraquinone N-oxide

A simple, highly selective and reproducible reversed-phase high-performance liquid chromatography method has been developed for the analysis of the new anti-cancer pro-drug AQ4N. The sample pre-treatment involves a simple protein precipitation protocol, using methanol. Chromatographic separations were performed using a HiChrom HIRPB (25 cmX4.6 mm I.D.) column, with mobile phase of acetonitrile-ammonium formate buffer (0.05 M) (22:78, v/v), with final pH adjusted to 3.6 with formic acid. The flow-rate was maintained at 1.2 ml min(-1). Detection was via photodiode array performed in the UV range at 242 nm and, since the compounds are an intense blue colour, in the visible range at 612 nm. The structurally related compound mitoxantrone was used as internal standard. The validated quantification range of the method was 0.05-10.0 microg ml(-1) in mouse plasma. The inter-day relative standard deviations (RSDs) (n=5) ranged from 18.4% and 12.1% at 0.05 microg ml(-1) to 2.9% and 3.3% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The intra-day RSDs for supplemented mouse plasma (n=6) ranged from 8.2% and 14.2% at 0.05 microg ml(-1) to 7.6% and 11.5% at 10.0 microg ml(-1) for AQ4N and AQ4, respectively. The overall recovery of the procedure for AQ4N was 89.4 +/- 1.77% and 76.1 +/- 7.26% for AQ4. The limit of detection was 50 ng ml(-1) with a 100 microl sample volume. The method described provides a suitable technique for the future analysis of low levels of AQ4N and AQ4 in clinical samples.     

Antiplasmodial activity of flavonol quercetin and its analogues in Plasmodium falciparum: evidence from clinical isolates in Bangladesh and standardized parasite clones

Malaria is still a major threat in many parts of the world with resistance spreading to almost all classes of antimalarials. The limited arsenal of available antimalarial drugs emphasizes the urgent need for novel antimalarial compounds. Owing to the fact that novel leads from nature have traditionally played a pivotal role in the development of various classes of antimalarials, we investigated a set of eight naturally occurring dietary flavonoids and their analogues for their antiplasmodial activity on clinical field isolates in southeastern Bangladesh and culture-adapted chloroquine-sensitive and chloroquine-resistant parasite clones. Except for taxifolin, all the other flavonoids had 50% inhibitory concentrations below 14 μM, both in the field and laboratory-adapted parasites. Neither of the flavonoids showed any activity correlation with chloroquine. The quercetin analogue rutin (7.10?±?10.32 μM) was the most active substance in field isolates as well as laboratory-adapted cultures (3.53?±?13.34 μM in 3D7 and 10.38?±?15.08 μM in K1), providing the first evidence of its activity against Plasmodium falciparum parasites. Thus, our results provide important evidence of the antimalarial activity of flavonoids in traditional use and thus warrant further investigation of these compounds as potential antiplasmodial agents.     

In vitro antibacterial activity of ceftizoxime on Pasteurella and EF4

The in vitro activity of ceftizoxime, a new third-generation cephalosporin, was tested by determining minimal inhibitory concentrations (MIC) by agar dilution method, for 150 strains of genus Pasteurella and group EF4 bacteria from various sources. All the strains were susceptible to ceftizoxime and inhibited by 0.03 micrograms/ml concentration. No significant difference appeared between the 7 species and human and animal strains. Group EF4 bacteria, frequently isolated from animal bite wounds in humans, had higher MIC (O.25-1 micrograms/ml). Results were compared to those obtained with cefotaxime, cephalothin, penicillin G and ampicillin.     

Microbial mutagenicity of isomeric two-, three-, and four-ring amino polycyclic aromatic hydrocarbons

The isomers of various two-, three-, and four-ring amino polycyclic aromatic hydrocarbons were tested for mutagenic activity using a microbial plate incorporation test with four Salmonella typhimurium strains (TA98, TA100, TA1535, and TA1537). All compounds were assayed with an S9 metabolic activating enzyme system. The two-ring compounds were tested only with TA98. All were weakly mutagenic (1-10 rev/micrograms) except 2-aminobiphenyl, which was not mutagenic under these test conditions. All except two of the 13 fused three-ring compounds (aminofluorenes, aminoanthracenes, and aminophenanthrenes) were active frame shift mutagens; only the aminophenanthrenes were active base-pair mutagens. The potency of this group of isomeric compounds ranged from moderately (approximately 20 rev/microgram) to strongly (greater than 5,000 rev/microgram) mutagenic. As a group, the pericondensed four-ring amino compounds were the most mutagenic of the three groups tested. All of the aminofluoranthene and aminopyrene isomers showed significant mutagenic activity with TA98, TA100, and TA1537. In general, the mutagenic potency of the amino polycyclic aromatic compounds tested was highly dependent on the structural position of the amino group.     

Molecular characterization of two recombinant potato virus Y isolates from China

Isolates of potato virus Y (PVY) have been divided into several strains. We determined the genomic sequences of PVY isolates AQ4 and FZ10 from tobacco in China. AQ4 and FZ10 had genome of 9700 and 9698 nucleotides, respectively. In phylogenetic analysis of complete genome sequences, AQ4 was clustered with strain N-Wi, and FZ10 with NTN. AQ4 had two recombination sites within the P1 and P3 genes, while FZ10 had three within the P1, P3 and NIa-Pro genes. When compared to typical NTN isolates, FZ10 lacked a recombination site within the CP gene and, thus, represents a novel recombination type of PVY.     

Synthesis of A/B-ring partial analogs of bruceantin as potential antimalarial agents

Bruceantin (1), a classical quassinoid with the highest reported antimalarial activity among the quassinoids examined thus far, was selected as a natural product lead for the design of a series of A/B-ring analogs. A viable strategy for the synthesis of the series was developed. The functionalized A-ring and the C-15 ester moiety in bruceantin are incorporated in all designed compounds. The preliminary bioassay results will be discussed in detail.     

Developing artemisinin based drug combinations for the treatment of drug resistant falciparum malaria: A review

The emergence and spread of drug resistant malaria represents a considerable challenge to controlling malaria. To date, malaria control has relied heavily on a comparatively small number of chemically related drugs, belonging to either the quinoline or the antifolate groups. Only recently have the artemisinin derivatives been used but mostly in south east Asia. Experience has shown that resistance eventually curtails the life-span of antimalarial drugs. Controlling resistance is key to ensuring that the investment put into developing new antimalarial drugs is not wasted. Current efforts focus on research into new compounds with novel mechanisms of action, and on measures to prevent or delay resistance when drugs are introduced. Drug discovery and development are long, risky and costly ventures. Antimalarial drug development has traditionally been slow but now various private and public institutions are at work to discover and develop new compounds. Today, the antimalarial development pipeline is looking reasonably healthy. Most development relies on the quinoline, antifolate and artemisinin compounds. There is a pressing need to have effective, easy to use, affordable drugs that will last a long time. Drug combinations that have independent modes of action are seen as a way of enhancing efficacy while ensuring mutual protection against resistance. Most research work has focused on the use of artesunate combined with currently used standard drugs, namely, mefloquine, amodiaquine, sulfadoxine/pyrimethamine, and chloroquine. There is clear evidence that combinations improve efficacy without increasing toxicity. However, the absolute cure rates that are achieved by combinations vary widely and depend on the level of resistance of the standard drug. From these studies, further work is underway to produce fixed dose combinations that will be packaged in blister packs. This review will summarise current antimalarial drug developments and outline recent clinical research that aims to bring artemisinin based combinations to those that need them most.     

An in silico 3D pharmacophore model of chalcones useful in the design of novel antimalarial agents

Malaria, the most important of the human parasitic diseases, causes about 500 million infections worldwide and over 1 million deaths every year. The search for novel drug candidates against specific parasitic targets is an important goal for antimalarial drug discovery. Recently the antimalarial activity of chalcones has generated great interest. These compounds are small non-chiral molecules with relative high lipophilicity (clogP approximately 5-7), have molecular weights in the range of 300 to 600 g/mol, and possess in vivo efficacy against both P. berghei and P. yeolii. Preliminary data on our on-going chalcone synthesis project indicate that these compounds are active in vitro against P. falciparum, but are rapidly metabolized in liver microsome assays. Structurally-related compounds not including the enone linker are found to be much more metabolically stable and yet have comparable in vitro efficacy. In this study, we have utilized the efficacy data from an in-house on-going chalcone project to develop a 3D pharmacophore for antimalarial activity and used it to conduct virtual screening (in silico search) of a chemical library which resulted in identification of several potent chalcone-like antimalarials. The pharmacophore is found to contain an aromatic and an aliphatic hydrophobic site, one hydrogen bond donor site, and a ring aromatic feature distributed over a 3D space. The identified compounds were not only found to be potent in vitro against several drug resistant and susceptible strains of P. falciparum and have better metabolic stability, but included one with good in vivo efficacy in a mouse model of malaria.