Coumarins and carbazoles with antiplasmodial activity from Clausena harmandiana

Activity guided fractionation of extracts from Clausena harmandiana have led to the identification of four known compounds, heptaphylline (1), clausine K (2), dentatin (5), and clausarin (6). All these compounds, except clausine K (2), exhibited antiplasmodial activity against Plasmodium falciparum. While the new dimethylated derivative 4, derived from 2, showed no antiplasmodial activity, the monomethylated product 3 (clausine H) exhibited activity comparable to that observed for compounds 1 and 5.     

Sipandinolide: a butenolide including a novel type of carbon skeleton from Siparuna andina

From a lipophilic extract of leaves of Siparuna andina (Monimiaceae), which exhibited antiplasmodial activity in vitro, two new compounds have been isolated: sipandinolide (1), a compound with a novel type of carbon skeleton and (-)-cis-3-acetoxy-4',5,7-trihydroxyflavanone (2). Their structures were established by spectroscopic methods; 2 showed moderate antiplasmodial activity whereas 1 was inactive.     

Antiplasmodial phenolic compounds from Piptadenia pervillei

Piptadenia pervillei Vatke (Fabaceae) was selected from a screening programme devoted to the search of naturally-occuring antimalarial compounds from plants of Madagascar. Bioassay-guided fractionation of the ethyl acetate extract of the leaves led to the isolation of four phenolic compounds, (+)-catechin ( 1), (+)-catechin 5-gallate ( 2), (+)-catechin 3-gallate ( 3) and ethyl gallate ( 4). Structures were determined by NMR and mass spectroscopy. Compounds 2 and 3 displayed the highest in vitro activity against the chloroquine-resistant strain FcB1 of Plasmodium falciparum with IC (50) values of 1.2 microM and 1.0 microM, respectively, and no significant cytotoxicity against the human embryonic lung cells MRC-5 was measured (IC (50) values > 75 microM). Five analogues ( 5 - 9) of (+)-catechin 5-gallate ( 2) were synthesized and evaluated for their antiplasmodial activity.     

Synthesis,cytotoxicity, and antiplasmodial and antitrypanosomal activity of new neocryptolepine derivatives

On the basis of the original lead neocryptolepine or 5-methyl-5H-indolo[2,3-b]quinoline, an alkaloid from Cryptolepis sanguinolenta, derivatives were prepared using a biradical cyclization methodology. Starting from easily accessible educts, this approach allowed the synthesis of hitherto unknown compounds with a varied substitution pattern. As a result of steric hindrance, preferential formation of the 3-substituted isomers over the 1-substituted isomers was observed when cyclizing N-(3-substituted-phenyl)-N'-[2-(2-trimethylsilylethynyl)phenyl]carbodiimides. All compounds were evaluated for their activity against chloroquine-sensitive as well as chloroquine-resistant Plasmodium falciparum strains, for their activity against Trypanosoma brucei and T. cruzi, and for their cytotoxicity on human MRC-5 cells. Mechanisms of action were investigated by testing heme complexation using ESI-MS, inhibition of beta-hematin formation, DNA interactions (DNA-methyl green assay and linear dichroism), and inhibition of human topoisomerase II. Neocryptolepine derivatives with a higher antiplasmodial activity and a lower cytotoxicity than the original lead have been obtained. This selective antiplasmodial activity was associated with inhibition of beta-hematin formation. 2-Bromoneocryptolepine was the most selective compound with an IC(50) value against chloroquine-resistant P. falciparum of 4.0 microM in the absence of cytotoxicity (IC(50) > 32 microM). Although cryptolepine, a known lead for antimalarials also originally isolated from Cryptolepis sanguinolenta, was more active (IC(50) = 2.0 microM), 2-bromoneocryptolepine showed a low affinity for DNA and no inhibition of human topoisomerase II, in contrast to cryptolepine. Although some neocryptolepine derivatives showed a higher antiplasmodial activity than 2-bromocryptolepine, these compounds also showed a higher affinity for DNA and/or a more pronounced cytotoxicity. Therefore, 2-bromoneocryptolepine is considered as the most promising lead from the present work for new antimalarial agents. In addition, 2-bromo-, 2-nitro-, and 2-methoxy-9-cyanoneocryptolepine exhibited antitrypanosomal activity in the micromolar range in the absence of obvious cytotoxicity.     

Antiplasmodial alkaloids from the stem bark of Strychnos malacoclados

From the stem bark of Strychnos malacoclados, one new bisindole alkaloid, 3-hydroxylongicaudatine Y (1), was isolated along with the known alkaloids vomicine (2), bisnordihydrotoxiferine (3), divarine (4), longicaudatine (5), longicaudatine Y (6), and longicaudatine F (7). All the compounds were tested for their antimalarial activity against the chloroquine-sensitive 3D7 and -resistant W2 strains of Plasmodium falciparum. Longicaudatine was the most active compound with IC?? values of 0.682 and 0.573 μM, respectively. The activity of compounds 1, 3, 4, 6, and 7 against the two strains ranged from 1.191 to 6.220 μM and 0.573 to 21.848 μM, respectively. Vomicine (2), the only monomer isolated, was inactive. The alkaloids of the longicaudatine-type ( 1, 5-7) were more active than those of the caracurine-type (3- 4). The presence of the ether bridge in the molecule seems to increase the antiplasmodial activity. Compounds 1, 5, and 7 were tested against the WI-38 human fibroblast cell line. Longicaudatine was the most cytotoxic compound with an IC?? of 2.721 μM. Longicaudatine F was 40-46 times more active against the two strains of P. falciparum than against the human fibroblasts and was thus considered as the more selective alkaloid. The structures of the compounds were determined based on the analysis of their spectral data.     

Antiplasmodial activity of ferrocenyl chalcones: investigations into the role of ferrocene.

A series of ferrocenyl chalcones were synthesized and evaluated in vitro against Plasmodium falciparum (K1) in a [3H] hypoxanthine uptake assay. Appropriate size, electronic, lipophilic and electrochemical parameters were determined for QSAR analysis. The results showed that the location of ferrocene influenced the ease of oxidation of Fe2+ in ferrocene and the polarity of the carbonyl linkage. These parameters were found to influence antiplasmodial activity. A general trend was noted in which compounds with ferrocene adjacent to the carbonyl linkage (series A) were associated with more selective and potent antiplasmodial activities. These compounds had polarized carbonyl linkages, lower lipophilicities and ferrocene rings that were less readily oxidized. The most active analogue was 1-ferrocenyl-3-(4-nitrophenyl)prop-2-en-1-one (28) (IC50 4.6 microM, selectivity index 37 against KB3-1 cells). To understand how the redox properties of ferrocene might influence antiplasmodial activity, the oxidant properties of selected compounds were investigated in antioxidant (ABTS+) and EPR experiments. The incorporation of ferrocene in the chalcone template was found to enhance its role in processes that involved the quenching and generation of free radicals. Thus, ferrocene may participate in redox cycling and this process may contribute to the antiplasmodial activity of ferrocenyl chalcones. However, the extent to which this property is manifested is also influenced by other physicochemical properties (lipophilicity, polarity, and planarity) of the compound.     

Synthesis of some cryptolepine analogues, assessment of their antimalarial and cytotoxic activities, and consideration of their antimalarial mode of action

A series of analogues of cryptolepine (1) have been synthesized and evaluated for their in vitro antiplasmodial and cytotoxic properties. The IC(50) values of several compounds (11a, 11k-m, 11o, 13) against Plasmodium falciparum (strain K1) were <0.1 muM, 5-10-fold lower than that of 1 but their cytotoxicities were only 2-4 times greater than that of 1. Compounds with a halogen in the quinoline ring and a halogen or a nitro group in the indole ring have enhanced antiplasmodial activity. In mice infected with P. berghei, the 7-bromo-2-chloro (11k) and 2-bromo-7-nitro (13) derivatives of 1 suppressed parasitemia by >90% at doses of 25 mg kg(-1) day(-1) with no apparent toxicity to the mice. 2,7-Dibromocryptolepine (15) was evaluated at several dose levels, and a dose-dependent suppression of parasitemia was seen (ED(90) = 21.6 mg kg(-1) day(-1)). The antimalarial mode of action of 1 appears to be similar to that of chloroquine and involves the inhibition of hemozoin formation. A number of analogues were assessed for their effects on the inhibition of beta-hematin (hemozoin) formation, and the results were compared with their antiplasmodial activities having taken account of their predicted accumulation into the acidic parasite food vacuole. No correlation was seen (r(2) = 0.0781) suggesting that the potent antimalarial activity of compounds such as 15 involves other mechanisms in addition to the inhibition of hemozoin formation.     

Cogniauxia podolaena: bioassay-guided fractionation of defoliated stems, isolation of active compounds, antiplasmodial activity and cytotoxicity

COGNIAUXIA PODOLAENA Baill. (Cucurbitaceae) is traditionally used in Congo Brazzaville for the treatment of malaria. We assessed the antiplasmodial activity of the plant and isolated some of the compounds responsible for this activity. It was the first time that a chemical study of this plant has been undertaken. Three triterpenes were isolated: cucurbitacin B ( 1), cucurbitacin D ( 2) and 20-epibryonolic acid ( 3) and their structures were assigned from spectroscopic evidence and comparison with published data. The crystallographic structure of 3 was determined. All fractions and compounds obtained in this study were assayed for antiplasmodial activity (on FcM29, a chloroquine-resistant strain of P. FALCIPARUM) and cytotoxicity (on KB and Vero cell lines). The IC50 values of 1, 2 and 3 are 1.6, 4 and 2 microg/mL on FcM29. Both 1 and 2 have a high cytotoxicity whereas 3 shows a better selectivity index.     

In vitro antiplasmodial activity of abietane and totarane diterpenes isolated from Harpagophytum procumbens (devil's claw)

The development of drug resistance and resurgence of malaria has highlighted the need for new chemically diverse antimalarial drugs. This study investigates Harpagophytum procumbens DC. as a source of antiplasmodial hit compounds. The roots of wild harvested plants as well as the aerial sections, seeds and roots of cultivated H. procumbens were evaluated for in vitro antiplasmodial activity. Bioassay-guided fractionation of the petroleum ether root extract yielded two diterpenes, (+)-8,11,13-totaratriene-12,13-diol (1) and (+)-8,11,13-abietatrien-12-ol (2). Compounds 1 and 2 displayed significant (IC50 < 1 microg/mL) in vitro antiplasmodial activity against a chloroquine-resistant (K1) and -sensitive (D10) strain of Plasmodium falciparum, and low cytotoxicity (SI > 65) against two mammalian cell lines (CHO and HepG2). It was found that 1 and 2 did not modify the erythrocyte shape, which in conjunction with the cytotoxicity results, indicates selective antiplasmodial activity.     

High antiplasmodial activity of novel plasmepsins I and II inhibitors

The aim of this study was to develop new antiplasmodial compounds acting through distinct mechanisms during both the liver and the blood stages of the parasite life cycle. Compounds were designed on the basis of the "double-drug" approach: primaquine, which has been linked to statine-based inhibitors of plasmepsins (PLMs), the plasmodial aspartic proteases involved in degradation of hemeoglobin. The compounds were tested in vitro for anti-PLM I/PLM II activities and against chloroquine-sensitive (D10) and chloroquine-resistant (W2) strains of P. falciparum. An antiplasmodial activity (IC(50)) as low as 0.1 microM was obtained, an excellent improvement in comparison with inhibitors previously reported (IC(50) = 2-20 microM). The killing activity was equally directed against both P. falciparum strains and was correlated to lipophilicity (calculated as ALogP), for all compounds but one (9). All compounds inhibited PLM I and PLM II in the nanomolar range (K(i) = 1-700 nM). The most promising compounds (2, 6, 10) were not cytotoxic against human fibroblasts at 100 microM and were highly selective for PLMs vs human cathepsin D.     

Antioxidant, antimalarial and antimicrobial activities of tannin-rich fractions, ellagitannins and phenolic acids from Punica granatum L

The Punica granatum L. (pomegranate) by-product POMx was partitioned between water, EtOAc and n-BuOH, and the EtOAc and n-BuOH extracts were purified by XAD-16 and Sephadex LH-20 column chromatography to afford ellagic acid (1), gallagic acid (2), punicalins (3), and punicalagins (4). Compounds 1 - 4 and the mixture of tannin fractions (XAD-16 eluates) were evaluated for antioxidant, antiplasmodial, and antimicrobial activities in cell-based assays. The mixture of tannins (TPT), XAD-EtOAc, XAD-H2O, XAD-PJ and XAD-BuOH, exhibited IC50 values against reactive oxygen species (ROS) generation at 0.8 - 19 microg/mL. Compounds 1 - 4 showed IC50 values of 1.1, 3.2, 2.3 and 1.4 microM, respectively, against ROS generation and no toxicity up to 31.25 microg/mL against HL-60 cells. Gallagic acid (2) and punicalagins (4) exhibited antiplasmodial activity against Plasmodium falciparum D6 and W2 clones with IC50 values of 10.9, 10.6, 7.5 and 8.8 microM, respectively. Fractions XAD-EtOAc, XAD-BuOH, XAD-H2O and XAD-PJ compounds 1 - 4 revealed antimicrobial activity when assayed against Escherichia coli, Pseudomonas aeruginosa, Candida albicans, Cryptococcus neoformans, methicillin-resistant Staphylococcus aureus (MRSA), Aspergillus fumigatus and Mycobacterium intracellulare. Compounds 2 and 4 showed activity against P. aeruginosa, C. neoformans, and MRSA. This is the first report on the antioxidant, antiplasmodial and antimicrobial activities of POMx isolates, including structure-activity relationships (SAR) of the free radical inhibition activity of compounds 1 - 4. Our results suggest a beneficial effect from the daily intake of POMx and pomegranate juice (PJ) as dietary supplements to augment the human immune system's antioxidant, antimalarial and antimicrobial capacities.     

Inhibition of the in vitro growth of Plasmodium falciparum by acyclic nucleoside phosphonates.

Forty-eight acyclic nucleoside phosphonates (putative prodrugs of acyclic nucleoside triphosphate inhibitors of DNA replication) have been evaluated for in vitro antiplasmodial activity. Only certain purine derivatives with a hydroxyl group attached to the acyclic sugar moiety displayed antiplasmodial activity. The two most active analogs were (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine ((S)-HPMPA, IC50=0.18+/-0.07 microM) and (S)-3-deaza-HPMPA (IC50=0.29+/-0.08 microM). Their cyclic derivatives, containing an ester bond between the phosphonate and the hydroxyl group, were slightly less active. All tested compounds that lacked the hydroxyl group, including potent antiretrovirus analogs such as 9-(2-phosphonylmethoxyethyl)adenine (PMEA) and the (S)-HPMPA derivatives (R)-PMPA and (S)-FPMPA, did not show any activity, even at very high concentrations ( >250 microM). Similarly, pyrimidine analogs of (S)-HPMPA, such as (S)-HPMPT, (S)-HPMPU and the anti-herpesvirus analog (S)-1-(3-hydroxy-2-phosphonylmethoxypropyl) cytosine ((S)-HPMPC), were devoid of any antiplasmodial activity. In addition, 11 acyclic nucleoside (non-phosphorylated) analogs--which in contrast to the acyclic nucleoside phosphonates require the presence of a monophosphorylating enzyme for the first activation step--were tested. None of them inhibited the growth of the parasite. In short three chemical entities seem to be imperative for antiplasmodial activity: a purine base, a hydroxyl group in the acyclic side chain and a phosphonate group terminating this chain.     

Antiplasmodial quinones from Pentas longiflora and Pentas lanceolata

The dichloromethane/methanol (1:1) extracts of the roots of Pentas longiflora and Pentas lanceolata showed low micromolar (IC(50) =?0.9-3?μg/mL) IN VITRO antiplasmodial activity against chloroquine-resistant (W2) and chloroquine-sensitive (D6) strains of PLASMODIUM FALCIPARUM. Chromatographic separation of the extract of PENTAS LONGIFLORA led to the isolation of the pyranonaphthoquinones pentalongin (1) and psychorubrin (2) with IC(50) values below 1?μg/mL and the naphthalene derivative mollugin (3), which showed marginal activity. Similar treatment of Pentas lanceolata led to the isolation of eight anthraquinones ( 4-11, IC(50) =?5-31?μg/mL) of which one is new (5,6-dihydroxydamnacanthol, 11), while three--nordamnacanthal (7), lucidin-ω-methyl ether (9), and damnacanthol (10)--are reported here for the first time from the genus Pentas. The compounds were identified by NMR and mass spectroscopic techniques.     

Biological Activities of the Chemical Constituents of<Emphasis Type="Italic">Erythrina stricta</Emphasis> and<Emphasis Type="Italic">Erythrina subumbrans</Emphasis>

Phytochemical investigation of the hexane and CH2Cl2 extracts of Erythrina stricta roots and E. subumbrans stems led to the isolation of six pterocarpans, one flavanone, one isoflavone, two alkaloids, five triterpenes, six steroids and alkyl trans-ferulates. The structures of all known compounds were determined on the basis of spectroscopic evidence. Sophoradiol (15), a mixture of stigmast-4-en-3-one (19) and stigmasta-4,22-dien-3-one (20), lupeol (21), cycloeucalenol (22), a mixture of 3beta-hydroxystigmast-5-en-7-one (23) and 3beta-hydroxystigmast-5,22-dien-7-one (24) and melilotigenin C (25) were first isolated from the genus Erythrina. The isolated compounds were evaluated for antiplasmodial activity, antimycobacterial activity and cytotoxicity. Among the tested compounds, 5-hydroxysophoranone (8) exhibited the highest antiplasmodial activity against Plasmodium falciparum (IC50 2.5 microg/mL). Compound 8, erystagallin A (5), erycristagallin (7) and erysubin F (10) showed the same level of antimycobacterial activity against Mycobacterium tuberculosis (MIC 12.5 microg/mL). For cytotoxicity, erybraedin A (2) showed the highest activity against the NCI-H187 and BC cells (IC50 2.1 and 2.9 microg/mL, respectively), whereas 10 exhibited the highest activity against the KB cells (IC50 4.5 microg/mL).     

Dual-acting diamine antiplasmodial and chloroquine resistance modulating agents

On the basis of structural features known to be critical for the antimalarial activity, accumulation and uptake of chloroquine (CQ), as well as chemosensitization of CQ resistant Plasmodium falciparum, an exploratory novel series of potential dual acting antiplasmodial and chemosensitizing agents was designed and synthesized for biological evaluation. All four compounds contain a common alkyl side chain with two amino groups and differ only in the chemical nature of the hydrophobic aromatic moieties. Among them, N'-[4-(biphenyl-2-ylmethoxy)-benzyl]-N,N-dimethyl-propane-1,3-diamine (P7) displayed the greatest potential as a dual-acting antiplasmodial agent against CQ-resistant strains (IC50K1/RSA11<0.6 microM) and chemosensitizer (RMIK1=0.67; RMIRSA11=0.82) while displaying low in vitro cytotoxicity against a mammalian cell line (CHO). At 1 microM, P7 caused a 8.5 and 4-fold potentiation in CQ accumulation in resistant P. falciparum K1 and RSA11 strains, respectively. In a parallel experiment, 1 microM verapamil showed a 6.5 (K1) and 2 (RSA11)-fold increase in CQ accumulation. The preliminary studies point to structural features that may determine antiplasmodial and/or CQ resistance modulating activity in this new series of compounds. An additive effect was observed against both CQS (D10) and CQR (RSA11) strains when CQ and P7 were used at their corresponding IC50 concentrations in isobologram analysis.     

Combretastatins D-3 and D-4, new macrocyclic lactones from Getonia floribunda

Chemical investigation of biologically active compounds of Getonia floribunda led to the isolation of two new macrocyclic lactones, combretastatins D-3 (1) and D-4 (2). The structures of these compounds were confirmed by spectroscopic analyses. Combretastatin D-3 (1) exhibited cytotoxicity towards the small-cell lung cancer cell line (NCI-H187, IC50=13.0 +/- 0.2 microg/mL) but was inactive against KB, BC-1, and Vero cell lines. Combretastatin D-3 (1) showed weak antitubercular activity with a minimum inhibitory concentration (MIC) of 100.0 microg/mL, and was inactive towards the malarial parasite. Combretastatin D-4 (2) was inactive in all antitubercular, antiplasmodial, and cytotoxic assays.     

Lepadins D-F: antiplasmodial and antitrypanosomal decahydroquinoline derivatives from the tropical marine tunicate Didemnum sp

From a new tunicate species, belonging to the genus Didemnum, three alkaloids possessing an unusual and extremely rare decahydroquinoline skeleton and showing significant and selective antiplasmodial and antitrypanosomal activity were obtained as follows: (2R*,3S*,4aR*,5R*,8aS*)-decahydro-3-hydroxy-5-(5'-hydroxyoctyl)-2-methylquinoline (lepadin D,1), its quaternary nitrogen derivative (2), (2R*,2"E,3S*,4aR*,5R*,8aS*)-decahydro-3-hydroxy-5-(5'-hydroxyoctyl)-2-methyl-3-quinolinyl ester 2"-octenoic acid (lepadin E, 3), and (2S*,2"E,3S*,4aR*,5R*,8aS*)-decahydro-3-hydroxy-5-(5'-hydroxyoctyl)-2-methyl-3-quinolinyl ester 2"-octenoic acid (lepadin F, 4). These isolates may well serve as lead structures for the development of new antimalarial drugs.     

Antiparasitic and antimicrobial indolizidines from the leaves of Prosopis glandulosa var. glandulosa

A new indolizidine alkaloid, named Δ1,?-juliprosopine (1), together with previously known indolizidine analogs (2- 6), was isolated from the leaves of Prosopis glandulosa var. glandulosa, collected from Nevada, USA; while two other known indolizidines, juliprosopine (6) and juliprosine (7), were isolated from P. glandulosa leaves collected in Texas, USA. The structures of compound 1 and 7 were determined using a combination of NMR and MS techniques. Compound 7 exhibited potent antiplasmodial activity against Plasmodium falciparum D6 and W2 strains with IC (50) values of 170 and 150 ng/mL, respectively, while 1 was found to be less active (IC?? values 560 and 600?ng/mL, respectively). Both compounds were devoid of VERO cells toxicity up to a concentration of 23?800?ng/mL. The antileishmanial activity of indolizidines was evaluated against Leishmania donovani promastigotes, axenic amastigotes, and amastigotes in THP1 macrophage cultures. When tested against macrophage cultures, the tertiary bases (1, 3, 6) were found to be more potent than quaternary salts (2, 5, 7), displaying IC?? values between 0.8-1.7?μg/mL and 3.1-6.0?μg/mL, respectively. In addition, compound 7 showed potent antifungal activity against Cryptococcus neoformans and antibacterial activity against Mycobacterium intracellulare, while 1 was potent only against C. neoformans and weakly active against other organisms.     

3,5-Diaryl-2-aminopyridines as a novel class of orally active antimalarials demonstrating single dose cure in mice and clinical candidate potential

A novel class of orally active antimalarial 3,5-diaryl-2-aminopyridines has been identified from phenotypic whole cell high-throughput screening of a commercially available SoftFocus kinase library. The compounds were evaluated in vitro for their antiplasmodial activity against K1 (chloroquine and drug-resistant strain) and NF54 (chloroquine-susceptible strain) as well as for their cytotoxicity. Synthesis and structure-activity studies identified a number of promising compounds with selective antiplasmodial activity. One of these frontrunner compounds, 15, was equipotent across the two strains (K1 = 25.0 nM, NF54 = 28.0 nM) and superior to chloroquine in the K1 strain (chloroquine IC(50) K1 = 194.0 nM). Compound 15 completely cured Plasmodium berghei-infected mice with a single oral dose of 30 mg/kg. Dose-response studies generated ED(50) and ED(90) values of 0.83 and 1.74 mg/kg for 15 in the standard four-dose Peters test. Pharmacokinetic studies in the rat indicated that this compound has good oral bioavailability (51% at 20 mg/kg) and a reasonable half-life (t(1/2) ～ 7-8 h).     

Flavonoids and isoflavonoids with antiplasmodial activities from the root bark of Erythrina abyssinica

From the root bark of Erythrina abyssinica a new pterocarpene [3-hydroxy-9-methoxy-10-(3,3-dimethylallyl)pterocarpene] and a new isoflav-3-ene [7,4'-dihydroxy-2',5'-dimethoxyisoflav-3-ene] were isolated. In addition, the known compounds erycristagallin, licoagrochalcone A, octacosyl ferulate and triacontyl 4-hydroxycinnamate were identified. The structures were determined on the basis of spectroscopic evidence. The crude extract and the flavonoids and isoflavonoids obtained from the roots of this plant showed antiplasmodial activities.