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PubMed2001

Antimalarial compounds from Rhaphidophora decursiva.

Bioassay-directed fractionation led to the isolation of 14 compounds, six of which possess antimalarial activity, from the dried leaves and stems of Rhaphidophora decursiva. Polysyphorin (1) and rhaphidecurperoxin (6) showed strong activities against Plasmodium falciparum. Rhaphidecursinol A (2), rhaphidecursinol B (3), grandisin (4), and epigrandisin (5) were less active against the same organism. Among the isolates, rhaphidecursinol A (2) and rhaphidecursinol B (3) were determined to be new neolignans, and rhaphidecurperoxin (6) is a new benzoperoxide. Known compounds isolated include polysyphorin (1), grandisin (4), epigrandisin (5), (+)-medioresinol, (-)-pinoresinol, (-)-syringaresinol, (+)-glaberide I, (+)-dehydrovomifoliol, (-)-liliolide, (-)-hydroxydihydrobovolide, and N-butylbenzamide, of which compound 1 appears worthy of further evaluation as an antimalarial agent. Structure elucidation and identification were accomplished by spectroscopic means including 1D and 2D NMR analyses.

Animals↗
PubMed2004

Isolation and structure elucidation of a novel antimalarial macrocyclic polylactone, menisporopsin A, from the fungus Menisporopsis theobromae.

An antimalarial macrocyclic polylactone, menisporopsin A (1), was isolated from a cell extract of the seed fungus Menisporopsis theobromae. The structure of 1 was elucidated on the basis of spectroscopic analysis and chemical transformations, with the absolute configuration established by application of the modified Mosher method and by using chiral HPLC. Menisporopsin A (1) possesses an unprecedented residue, 2,4-dihydroxy-6-(2,4-dihydroxy-n-pentyl)benzoic acid. This compound exhibited antimalarial activity, with an IC(50) value of 4.0 microg mL(-1), and antimycobacterial activity (MIC value of 50 microg mL(-1)).

Animals↗
PubMedDate not supplied

Antimalarial agents, 2. Artesunate, an inhibitor of cytochrome oxidase activity in Plasmodium berghei.

The activity of the cytochrome oxidase, which is located in the plasma and the nuclear and the food-vacuole-limiting membranes as well as in the mitochondria of the trophozoites of Plasmodium berghei, was inhibited completely by sodium artesunate, an antimalarial drug, in vitro at 1 mM and in vivo at 100 mg/kg iv. This enzyme appears to be a target for the antimalarial mechanism of action of artesunate and qinghaosu.

Animals↗
PubMedDate not supplied

Antimalarial agents, 4. Synthesis of a brusatol analog and biological activity of brusatol-related compounds.

The quassinoids bruceoside-A [1], brusatol [2], and bruceolide [3] were tested for antimalarial activity in vitro against the chloroquine-resistant (Smith) isolates of Plasmodium falciparum. Compound 2 was quite active, 1 was not active, and 3 showed only a trace of activity. The fact that 15 [(E)-non-2-enoyl] bruceolide [7] synthesized from 2 was eight times less active than 2 would indicate that the requirement of a C-15 ester moiety for enhanced antimalarial activity among brusatol related quassinoids could be quite specific.

Animals↗
PubMed1993

A new antimalarial quassinoid from Simaba guianensis.

Two antimalarial quassinoids, gutolactone [1] and simalikalactone D [2], have been characterized by bioactivity-directed fractionation from the bark of Simaba guianensis collected near Manaus, Brazil. Compound 2 was previously isolated from Simaba multiflora and Quassia africana and shown to be an active antimalarial in vitro. This is the first occurrence of 1. The structure of the novel quassinoid was established by spectral methods including 2D nmr spectroscopy.

Animals↗
PubMed2006

Antimalarial activity of a new family of analogues of manzamine A.

Manzamine A represents an important lead structure for the development of novel antimalarial chemotherapies. The synthesis and biological evaluation of a group of simplified analogues of manzamine A, which were designed to examine the roles of the A and D rings and of both the relative stereochemistry and the orientation of the beta-carboline heterocycle on the antimalarial activity of manzamine A, are described. [structure: see text]

Animals↗
PubMed2001

Antimalarial drugs exacerbate rat liver microsomal lipid peroxidation in the presence of oxidants.

The study was undertaken to evaluate the effect of prior treatment of rats with the antimalarial drugs amodiaquine (AQ) mefloquine (MQ) and halofantrine (HF) on rat liver microsomal lipid peroxidation in the presence of 1 mM FeSO4, 1 mM ascorbate and 0.2 mM H2O2 (oxidants). Ingestion of alpha-tocopherol, a radical chain-breaking antioxidant was also included to assess the role of antioxidants in the drug treatment. In the presence of oxidants AQ, MQ and HF elicited 288%, 175% and 225% increases in malondialdehyde (MDA) formation while the drugs induced 125%, 63% and 31% increases in the absence of oxidants respectively. Similarly, AQ, MQ and HF induced lipid hydroperoxide formation by 380%, 256%, 360% respectively in the presence of oxidants and 172%, 136% and 92% in the absence of exogenously added oxidants respectively. a-tocopherol reduced AQ, MQ and HF-induced MDA formation by 40%, 55% and 52% respectively and lipid hydroperoxide formation by 53%, 59% and 54% respectively. Similarly, alpha-tocopherol attenuated the AQ, MQ and HF-induced MDA formation by 49%, 51% and 51% in the presence of oxidants and lipid hydroperoxide formation by 61%, 62% and 47% respectively. The results indicate that rat liver microsomal lipid peroxidation could be enhanced by antimalarial drugs in the presence of reactive oxygen species and this effect could be ameliorated by treatment with antioxidants.

Amodiaquine↗
PubMed1990

Effect of aliphatic side-chain substituents on the antimalarial activity and on the metabolism of primaquine studied using mitochondria and microsome preparations.

The substitution of two deuterium atoms on the alpha-carbon of the primaquine side chain was found to produce a sevenfold decrease in the rate of conversion of primaquine to carboxyprimaquine by enzymatic oxidative deamination, but the deuterium substitution was found to have no significant effect on the in vitro antimalarial activity or on in vitro hepatocyte toxicity. Placing a single methyl group on the alpha-carbon was found to produce only a slight decrease in the rate of oxidative deamination. Although metabolic attack occurred adjacent to either the aniline nitrogen or the aliphatic amine, metabolic attack occurred primarily adjacent to the more basic nitrogen at the 1'-position, even when this position bore a methyl substituent. Primaquine, the alpha-dideutero analogue, and the alpha-methyl analogue were all found to have about the same in vitro antimalarial activity as determined in the liver hepatocyte assay.

Animals↗
PubMed1999

Dipeptide derivatives of primaquine as transmission-blocking antimalarials: effect of aliphatic side-chain acylation on the gametocytocidal activity and on the formation of carboxyprimaquine in rat liver homogenates.

PURPOSE: Dipeptide derivatives of primaquine (PQ) with reduced oxidative deamination to the inactive metabolite carboxyprimaquine were synthesized and evaluated as a novel class of transmission-blocking antimalarials. METHODS; Antimalarial activity was studied using a model consisting of mefloquine-resistant Plasmodium berghei ANKA 25R/10, Balb C mice, and Anopheles stephensi mosquitoes. Metabolic studies were performed with rat liver homogenates, and the incubates were analyzed by HPLC. RESULTS: All dipeptide derivatives and glycyl-PQ completely inhibited the appearance of oocysts in the midguts of the mosquitoes at 15 mg/ kg, while N-acetylprimaquine was not active at this dose. However, none of the title compounds were able to block oocyst production at 3.75 mg/kg, in contrast with primaquine. Exception for sarc-gly-PQ, all remaining compounds prevented sporozoite formation in the salivary glands of mosquitoes at a dose of 3.75 mg/kg. Simultaneous hydrolysis to primaquine and gly-PQ ocurred with the following order of Vmax/Km: for primaquine formation. L-ala-gly-PQ > L-phe-gly-PQ > gly-gly-PQ; and for gly-PQ formation, L-phe-gly-PQ > L-ala-gly-PQ > gly-gly-PQ. In contrast, primaquine was not released from D-phe-gly-PQ, sarc-gly-PQ, and N-acetylprimaquine. Neither carboxyprimaquine nor 8-amino-6-methoxyquinoline were detected in any of the incubation mixtures. CONCLUSIONS: The title compounds prevent the development of the sporogonic cycle of Plasmodium berghei. Gametocytocidal activity is independent of the rate and pathway of primaquine formation. Acylation of the aliphatic side-chain effectively prevents the formation of carboxyprimaquine, but the presence of a terminal amino group appears to be essential for the gametocytocidal activity.

Acylation↗
PubMed1993

Decomposition of arteether in simulated stomach acid yielding compounds retaining antimalarial activity.

In simulated stomach acid (aqueous 0.01 M HCl, 37 degrees C) beta-arteether decomposed (half-life, 441 +/- 17 min) to dihydroartemisinin, which subsequently rearranged to a new compound (1) having an endoperoxide group and an aldehyde group. The in vitro antimalarial activity of dihydroartemisinin is similar to that of beta-arteether, whereas compound 1 had approximately 1/10th the activity of beta-arteether. Compound 1 was prepared in sufficient quantities to afford samples for biological evaluation and a complete chemical characterization with 1H- and 13C-NMR and mass spectrometry. While beta-arteether would be somewhat unstable in the stomach, if the drug were administered on an empty stomach (emptying time, approximately 30 min) as a suspension or tablet, sufficient quantities of intact arteether may reach the small intestines, where it would be stable and readily absorbed. Its decomposition products, dihydroartemisinin and 1, may also contribute to the antimalarial activity of the administered drug following oral administration.

Animals↗
PubMed2003

Computational studies of new potential antimalarial compounds--stereoelectronic complementarity with the receptor.

One of the most important pharmacological mechanisms of antimalarial action is the inhibition of the aggregation of hematin into hemozoin. We present a group of new potential antimalarial molecules for which we have performed a DFT study of their stereoelectronic properties. Additionally, the same calculations were carried out for the two putative drug receptors involved in the referred activity, i.e., hematin mu-oxo dimer and hemozoin. A complementarity between the structural and electronic profiles of the planned molecules and the receptors can be observed. A docking study of the new compounds in relation to the two putative receptors is also presented, providing a correlation with the defined electrostatic complementarity.

Amino Acids↗
PubMed2002

Medical need, scientific opportunity and the drive for antimalarial drugs.

Continued and sustainable improvements in antimalarial medicines through focused research and development are essential for the world's future ability to treat and control malaria. Unfortunately, malaria is a disease of poverty, and despite a wealth of scientific knowledge there is insufficient market incentive to generate the competitive, business-driven industrial antimalarial drug research and development that is normally needed to deliver new products. Mechanisms of partnering with industry have been established to overcome this obstacle and to open up and build on scientific opportunities for improved chemotherapy in the future.

Animals↗
PubMed2005

Synthesis of 5'-methylenearisteromycin and its 2-fluoro derivative with potent antimalarial activity due to inhibition of the parasite S-adenosylhomocysteine hydrolase.

5'-methylenearisteromycin 5 and its 2-fluoro derivative 6, which were designed as antimalarial agents because of their AdoHcy hydrolase inhibition, were synthesized from D-ribose, using a stereoselective intramolecular radical cyclization as the key step to construct the carbocyclic structure. These compounds were evaluated as AdoHcy hydrolase inhibitors with the recombinant human and malarial parasite enzymes. Although 5 and 6 were both potent inhibitors of the malarial parasite AdoHcy hydrolase, the 2-fluoro derivative 6 proved to be superior due to its lower inhibitory effect on the human enzyme. In addition, 6 was identified as a potent antimalarial agent using an in vitro assay system with Plasmodium falciparum.

Adenosine↗
PubMed2005

Reaction of artemisinin with haemoglobin: implications for antimalarial activity.

Elucidation of the principal targets of the action of the antimalarial drug artemisinin is an ongoing pursuit that is important for understanding the action of this drug and for the development of more potent analogues. We have examined the chemical reaction of Hb with artemisinin. The protein-bound haem in Hb has been found to react with artemisinin much faster than is the case with free haem. It appears that the uptake of Hb and the accumulation of artemisinin into the food vacuole, together with the preferred reactivity of artemisinin with haem in Hb, may make Hb the primary target of artemisinin's antimalarial action. Both monoalkylated (HA) and dialkylated (HAA) haem derivatives of artemisinin have been isolated. These 'haemarts' bind to PfHRP II (Plasmodium falciparum histidine-rich protein II), inhibiting haemozoin formation, and possess a significantly decreased ability to oxidize ascorbic acid. The accelerated formation of HAA from Hb is expected to decrease the ratio of haem to its alkylated derivatives. The haemarts that are generated from 'haemartoglobins' may bring about the death of malaria parasite by a two-pronged effect of stalling the formation of haemozoin by the competitive inhibition of haem binding to its templates and creating a more reducing environment that is not conducive to the formation of haemozoin.

Alkylation↗
PubMed2003

Mapping of the Plasmodium falciparum multidrug resistance gene 5'-upstream region, and evidence of induction of transcript levels by antimalarial drugs in chloroquine sensitive parasites.

The Plasmodium falciparum multidrug resistance gene, pfmdr1, has been shown to be involved in the mediation of the parasite's response to various antimalarial drugs. Previous studies of pfmdr1 expression have shown that transcript levels are increased in drug-resistant isolates. However, a detailed examination of the transcriptional regulation of this gene has not been completed. The aim of this study was to map the 5' UTR of pfmdr1, and to examine the transcriptional profile of the gene in sensitive parasites treated with four different antimalarial drugs. RT-PCR and 5'-RACE mapping showed that the 5' UTR has a length of 1.94 kb. A putative promoter has been identified via transient transfection. Northern analysis revealed a 2.1- to 2.7-fold increase in pfmdr1 expression in 3D7 parasites treated with 50 nM chloroquine for 6 h, confirming results from Serial Analysis of Gene Expression. 3D7 parasites were subsequently treated with experimentally derived IC50 concentrations of mefloquine, quinine and pyrimethamine. pfmdr1 transcript levels specifically increased 2.5-fold at 6 h in mefloquine-treated parasites and threefold in parasites treated with quinine for 30 min. There was no evidence of transcript induction in pyrimethamine-treated parasites. This is the first evidence of induction of pfmdr1 expression in sensitive cells; and suggests a novel method of transcriptional control for this gene.

5' Untranslated Regions↗
PubMed1996

Plasmodium berghei mouse model: antimalarial activity of new alkaloid salts and of thiosemicarbazone and acridine derivatives.

Sixteen compounds were synthesized and evaluated on Plasmodium berghei in CD1 mouse. The nature of the salt associated to the active principle can give some advantages in the field of activity, bioavailability and toxicity. beta-Resorcylic acid was chosen in this study because of its previously described antimalarial activity and its expected enhancement of quinine antimalarial activity. While treatment with subcutaneous quinine sulphate at 1 mmol/kg cured 6/10 mice, quinine beta-resorcylate cured all the mice under identical conditions. Although such a result appeared promising, in vitro investigation should be performed to draw clear conclusions regarding a synergy between quinine and beta-resorcylate. Cinchonidine beta-resorcylate was also active; all mice were cured at 1 mmol/kg and the mean survival time was 13.8 +/- 2.4 days after a subcutaneous treatment at 0.5 mmol/kg in a single dose. In the series of acridines, (N-alpha, sigma-dioxopentyl)-5-amino-1,2,3,4-tetrahydroacridine cured all mice at 50 mumol/kg under the same conditions. The maximum tolerated doses in mice ranged from 100 to 150 mumol/kg for these acridine derivatives. The chemotherapeutic index of (N-alpha, sigma-dioxopentyl)-5-amino-1,2,3,4-tetrahydroacridine was estimated at 2-3. Other salts expected to reduce the toxicity, such as alpha-ketoglutarate and p-chlorophenoxyacetate, did not enhance the activity of the active principles. These results prompt us to further investigations including plasma kinetic evaluation in rats and in vitro on Plasmodium falciparum.

Acridines↗
PubMed2001

Authentication of artemether, artesunate and dihydroartemisinin antimalarial tablets using a simple colorimetric method.

The recent and widespread appearance of counterfeit antimalarial tablets in South-east Asia prompted the search for simple field assays to identify genuine drugs. In a recently described colorimetric assay for artesunate, Fast red TR salt reacted with an alkali-decomposition product of artesunate to produce a distinct yellow colour. However, that assay is specific for artesunate and it cannot be used to test for artemether. Because of potential concerns over artemether tablet counterfeiting, the colorimetric assay was modified to detect artemether, dihydroartemisinin and artesunate tablets. Other common antimalarials (artemisinin, chloroquine diphosphate, mefloquine HCl, sulphadoxine and pyrimethamine), as well as aspirin and acetaminophen, were negative in the assay, indicating its specificity for artemether, dihydroartemisinin and artesunate. The colorimetric method can be used to obtain a rapid visual assessment of tablet authenticity. The method can also be used to quantify the drug content of tablets, when used in conjunction with a spectrophotometer.

Antimalarials↗