Antiplasmodial anthraquinones and hemisynthetic derivatives from the leaves of Tectona grandis (Verbenaceae)

Chemical investigation of the methanol extract of the leaves of Tectona grandis led to the isolation of one new anthraquinone derivative, grandiquinone A (3-acetoxy-8-hydroxy-2-methylanthraquinone) (1), along with nine known compounds: 5,8-dihydroxy-2-methylanthraquinone (2), hydroxysesamone (3), 3-hydroxy-2-methylanthraquinone (4), quinizarine (5), betulinic acid (6), ursolic acid (7), tectograndone (8), corosolic acid (9) and sitosterol 3-O-β-d-glucopyranoside (10). Compounds 2 and 3 were isolated for the first time from the leaves of this plant, while 5 has never been reported from the genus Tectona. Hydroxysesamone (3) and tectograndone (8) were subjected to cyclisation and acetylation reactions to afford two hemisynthetic derivatives, 6,9-dihydroxy-2,2-(dimethyldihydropyrano)-3,4-dihydro-2H-benzo[g]chromene-5,10-dione (11) and acetyltectograndone (12) respectively, which are reported here for the first time. The ethyl acetate-soluble portion, some of the isolated compounds and hemisynthetic derivatives were evaluated for their antiplasmodial activity against the multidrug-resistant Dd2 strain of Plasmodium falciparum. Compound 3 showed a prominent activity, while 2, 8, 9, 11 and 12 showed significant in vitro anti-malarial activity. Compound 1 was weakly active in this test. The structures of the compounds were elucidated by spectroscopic methods and comparison of the data with the literature.     

Antiplasmodial and cytotoxic activity of lanostane type triterpenoids isolated from Leplaea mayombensis

Leplaeric acid E 5, leplazarin 6a and 21-epileplazarin 6b, three new 3,4-seco-lanostane type triterpenes have been isolated from the stem bark of Leplaea mayombensis (Pellegr.) Staner along with fourteen known compounds from the fruits and roots. Leplaeric acid E, leplazarin and 21-epileplazarin, 15-α-hydroxy-3,4-seco-lanosta-4(28),8,24-triene-3,21-dioic acid, mayomlactones A and B, lanosta-7,24-dien-3-one, leplaeric acid A, B and C were screened in vitro for antiplasmodial activity against chloroquine-sensitive (Pf3D7) and chloroquine-resistant (PfINDO) strains of Plasmodium falciparum and for cytotoxicity against CAL-27, CaCo2, Skov-3, and HepG2 cells line. Three compounds including 15-α-hydroxy-3,4-seco-lanosta-4(28),8,24-triene-3,21-dioic acid (IC₅₀ 5.65–7.09 μM), lanosta-7,24-dien-3-one (IC₅₀ 7.18–9.07 μM), and leplaeric acid C (IC₅₀ 7.59–8.47 μM) were the most active against both strains of P. falciparum. All the compounds exhibited cytotoxicity against the three-cell lines with IC₅₀ ranging from 12.30 to 181.88 μM. These results confirm the usage of the medicinal plant L. mayombensis for the management of malaria and suggest that further lead optimization studies on potent compounds identified from this study could lead to the identification of potential of lead molecules as scaffold for new antimalarial drug discovery.     

Tomoeones A-H, cytotoxic phloroglucinol derivatives from Hypericum ascyron

Phloroglucinol derivatives tomoeones A-H (1-8) and three known compounds were isolated from leaves of Hypericum ascyron. Their structures were established based on spectroscopic analyses. They are all acylphloroglucinol derivatives possessing a spiro skeleton with geminal isoprenyl groups and a monoterpene moiety, and they are stereoisomers to each other at C-4 and C-13. They appear to be a class of phloroglucinol derivatives. Cytotoxicities of the isolated phloroglucinol derivatives against human tumor cell lines, including multidrug-resistant (MDR) cancer cell lines, were evaluated. Tomoeone F (6) demonstrated significant cytotoxicity against KB cells with an IC50 value of 6.2 microM. Compound 6 was also cytotoxic against MDR cancer cell lines (KB-C2 and K562/Adr), which was more potent than doxorubicin.     

Antiplasmodial sesquiterpenes from the seeds of Salacia longipes var. camerunensis

Phytochemical investigation of the seeds of Salacia longipes var. camerunensis led to the isolation of four sesquiterpenoid derivatives, salaterpene A (1) (1α,2β,8β-triacetoxy-6β,9β-dibenzoyloxy-4β-hydroxy-dihydro-β-agarofuran), salaterpene B (2) (1α,2β,8β-triacetoxy-9β-benzoyloxy-6β-cinnamoyloxy-4β-hydroxy-dihydro-β-agarofuran), salaterpene C (3) (1α,2β-diacetoxy-6β,9β-dibenzoyloxy-4β-hydroxy-dihydro-β-agarofuran) and salaterpene D (4) (2β-acetoxy-1α,6β-dibenzoyloxy-4β-hydroxy-9β-nicotinoyloxy-dihydro-β-agarofuran) together with two known compounds (5 and 6). The structures of the compounds were established by means of NMR spectroscopy. Compounds 1–4 and 6 were tested in vitro for their antiplasmodial activity against Plasmodium falciparum chloroquine-resistant strain W2. All the tested compounds exhibited a moderate potency with IC₅₀ below 2.7 μM.     

Antiplasmodial and cytotoxicity evaluation of 3-functionalized 2-azetidinone derivatives

3-Azido-, 3-amino- and 3-(1,2,3-triazol-1-yl)-β-lactams were synthesized and evaluated for their antiplasmodial activity against four strains of Plasmodium falciparum and KB cells for their cytotoxicity profiles. The presence of a cyclohexyl substituent at N-1 and a phenyl group on the triazole ring markedly improved the activity profiles of triazole-tethered β-lactam exhibiting IC₅₀ values of 1.13, 1.21 and 1.00 μM against 3D7, K1 and W2 strains respectively.     

Antiplasmodial structure-activity relationship of 3-trifluoromethyl-2-arylcarbonylquinoxaline 1,4-di-N-oxide derivatives

Derivatives of 3-trifluoromethyl-2-arylcarbonylquinoxaline 1,4-di-N-oxide (4b-g, 5b-g, 6a-g) were synthesized and evaluated for their capacity to inhibit the growth of chloroquine-resistant Plasmodium falciparum FCB1 strain in culture. Compound 7-chloro-2-(2-furylcarbonyl)-3-trifluoromethyl-1,4-quinoxaline di-N-oxide (5g) was the most active being almost 5 times more active than chloroquine. It was also 50 times more active against P. falciparum than toxic toward MCF7 cells. Structural characteristics for a quinoxaline to be active were defined: bioisosteric modification of phenyl group by 2-thienyl or 2-furyl subunits, R2 position must be free or occupied by a methyl group and R1 position must be free or occupied by Cl, CH3, OCH3 or CF3.     

Antiplasmodial flavanones and a stilbene from Carpha glomerata

Bioassay-guided fractionation of an extract of Carpha glomerata (Cyperaceae) led to the isolation of seven compounds. Compounds 1 (carphorin A), 3 (carphorin C), 4 (carphorin D), and 5 (carphabene) are new compounds, and compound 2 (8-(3″-hydroxyisoamyl)-naringenin) was isolated for the first time as a natural product. All structures were elucidated based on analyses of their HR-ESIMS and 1D and 2D NMR data. Compounds 1, 2, and 6, which have prenyl or hydroxyprenyl side chains, exhibited antiplasmodial activities with IC₅₀ values of 5.2?±?0.6, 3.4?±?0.4, and 6.7?±?0.8?µM against the drug-resistant Dd2 strain of Plasmodium falciparum. In addition the prenylated stilbene 5 also showed good activity, with IC₅₀ 5.8?±?0.7?µM.     

Antiplasmodial constituents from the stem bark of Polyalthia longifolia var pendula

Along with two known compounds (1 and 2), four new clerodane diterpenes were isolated and identified from the stem bark of Polyalthia longifolia: cleroda-3-ene pyrrole-15,16-dione (3), cleroda-3-ene, pyrrolidine-15,16-dione (4), cleroda-3,13(14)E-diene-15,16-diamide (5), and cleroda-3-ene-15,16-diamide (6). Their structures were elucidated by combinations of NMR, MS and IR. Using the WHO Mark III Microtest assay, the isolated compounds were evaluated for their antiplasmodial effects. They showed antiplasmodial effects, with IC₅₀s ranging from 4.5 to 213.8 μM.     

Antiplasmodial and antimycobacterial cyclopeptide alkaloids from the root of Ziziphus mauritiana

Investigation of the MeOH extract obtained from the root of the Ziziphus mauritiana grown in Thailand resulted in the isolation of two 14- and 13-membered cyclic alkaloids, mauritine L (1) and mauritine M (2), and three known cyclopeptide alkaloids, nummularines H (3), B (4) and hemsine A (5). Their structures were elucidated on the basis of extensive NMR spectroscopic analysis. The first single crystal X-ray diffraction study of the 13-membered ring cyclopeptide, nummularine B methiodide (4′), revealed all S configurations on the amino acid residues. The isolated alkaloids exhibited potent antiplasmodial activity against the parasite Plasmodium falciparum with the inhibitory concentration (IC₅₀) ranging from 3.7 to 10.3 μM. Compounds 2 and 3 also demonstrated antimycobacterial activity against Mycobacterium tuberculosis with the MIC of 72.8 and 4.5 μM, respectively.     

Synthesis and evaluation of the antiplasmodial activity of novel indeno[2,1-c]quinoline derivatives

With the aim to explore the potentiality of new chemical scaffolds for the design of new antimalarials, a set of new indeno[2,1-c]quinolines bearing different basic heads has been synthesized and tested in vitro against chloroquine sensitive (CQ-S) and chloroquine resistant (CQ-R) strains of Plasmodium falciparum. Most of the synthesized compounds exhibited a moderate antiplasmodial activity, inhibiting the growth of both CQ-S and CQ-R strains of P. falciparum with IC₅₀ ranging from 0.24 to 6.9 μM and with a very low resistance index. The most potent compounds (1.2–1.3-fold the CQ on the W-2 strain) can be considered as promising ‘lead compounds’ to be further optimized to improve efficacy and selectivity against Plasmodia.     

Isolation of the New Antiplasmodial Butanolide,Malleastrumolide A,from Malleastrum sp. (Meliaceae) from Madagascar

An extract of Malleastrum sp. (Meliaceae) collected in Madagascar by the Madagascar International Cooperative Biodiversity Group was found to have antimalarial activity, with an IC ₅₀ value between 2.5 and 5 μg ml^?1. After purification by liquid‐liquid partition, chromatography on a Diaion open column, C ₁₈ SPE and C ₁₈ reversed phase HPLC , the new butanolide, malleastrumolide A, was isolated. The structure of malleastrumolide A was determined by mass spectrometry, NMR , and ECD . The double bond position was determined by cross‐metathesis and mass spectrometry. The compound has antiproliferative activity against the A2780 ovarian cancer cell line with an IC ₅₀ value of 17.4 μm and antiplasmodial activity against the drug‐resistant Dd2 strain of Plasmodium falciparum with an IC ₅₀ value of 2.74 μm .     

Bioactive Neolignans and Other Compounds from Magnolia grandiflora L.: Isolation and Antiplasmodial Activity

Bioassay‐guided fractionation of a methanol extract of Magnolia grandiflora against Plasmodium falciparum yielded two new ( 1 and 2 ) and six known ( 3 – 8 ) bioactive compounds. The structures of the new compounds were assigned by mass spectrometric and 1D‐ and 2D‐NMR data. Known compounds were identified by comparison of ¹H‐NMR and MS data with literature data. The two known neolignans 3 and 4 showed moderate antiplasmodial activity with the IC₅₀ values of 2.8 ± 0.1 and 3.4 ± 0.1 μm , respectively. Weak antiplasmodial activity was recorded for compounds 1 , 2 , 5 , 6 , 7 , and 8 , with the IC₅₀ values of 38 ± 2, 23 ± 2, 16.5 ± 0.2, 86 ± 1, 44 ± 4, and 114 ± 9 μm , respectively.     

Anti-inflammatory phloroglucinol derivatives from Hypericum empetrifolium

Phytochemical investigation of Hypericum empetrifolium Willd. (Clusiaceae), a species native to Greece and Turkey has led to the bioassay-guided identification of two acylphloroglucinol derivatives with potent in vitro anti-inflammatory activity. Using NMR spectroscopy and mass spectrometry, the acylphloroglucinol derivatives were characterized as 3-geranyl-1-(2'-methylpropanoyl)phloroglucinol (1) and 3-geranyl-1-(2'-methylbutanoyl)phloroglucinol (2). Hypotheses are proposed regarding the biosynthetic origin of these and similar acylphloroglucinols from related Hypericum species. Compounds 1 and 2 were evaluated for in vitro inhibitory activity against COX-1, COX-2 and 5-LOX catalyzed LTB(4) formation. Compound 1 displayed good activity (IC(50) values: 6.0, 29.9, and 2.2 μM, respectively) in all three assays. Compound 2 showed good activity (IC(50) value: 5.8 μM) against LTB(4) formation and moderate activity (IC(50) value: 26.2 μM) against COX-1.     

Antiplasmodial activities of gold(I) complexes involving functionalized N-heterocyclic carbenes

A series of twenty five molecules, including imidazolium salts functionalized by N-, O- or S-containing groups and their corresponding cationic, neutral or anionic gold(I) complexes were evaluated on Plasmodium falciparum in vitro and then on Vero cells to determine their selectivity. Among them, eight new compounds were synthesized and fully characterized by spectroscopic methods. The X-ray structures of three gold(I) complexes are presented. Except one complex (18), all the cationic gold(I) complexes show potent antiplasmodial activity with IC₅₀ in the micro- and submicromolar range, correlated with their lipophilicity. Structure–activity relationships enable to evidence a lead-complex (21) displaying a good activity (IC₅₀ = 210 nM) close to the value obtained with chloroquine (IC₅₀ = 514 nM) and a weak cytotoxicity.     

Antiplasmodial alkaloids from bulbs of Amaryllis belladonna Steud.

A bioassay-guided fractionation and chemical investigation of Amaryllis belladonna Steud. bulbs resulted in the isolation and identification of the new crinane alkaloid 1,4-dihydroxy-3-methoxy powellan (1), along with the 3 known crinane alkaloids 2–4 and the two lycorane alkaloids 5–6. The structures were elucidated by interpretation of combined HR-ESIMS, CD and 2D NMR spectroscopic data. Among these isolated compounds the lycorane-type alkaloid acetylcaranine (5) exhibited strong antiplasmodial activity, while compounds 3 and 4 were moderately active, and compounds 1 and 6 were inactive.     

Antiplasmodial and cytotoxicity activities of some selected plants used by the Maasai community, Kenya

Malaria has continued to be a major global public health problem and a health concern in most of African countries. An estimated 350–500 million cases of malaria each year result in about one million deaths, mainly children under five. The rate of malaria infection is increasing rapidly partly due to drug resistance by the Plasmodium falciparum. The cost of the current drugs is prohibitive to the poor. There is therefore urgent need to identify new antimalarial agents that are effective, safe and affordable. In our continuous search for these new antimalarial compounds, extracts from five medicinal plants from the Maasai community in Kenya were tested against P. falciparum (D6; chloroquine sensitive and W2; chloroquine resistant strains). Of the tested total plant extracts, 5 crude extracts showed good antiplasmodial activity against D6 strain of P. falciparum with IC₅₀ values lower or equal to 14.3 μg/ml, 2 were moderately active with IC₅₀ values in between 26.6 and < 50 μg/ml. The petroleum ether extracts of the aerial parts and roots of Fuerstia africana demonstrated high antiplasmodial activity against the chloroquine sensitive antiplasmodial strain D6 (IC₅₀ 1.5 and 4.6 μg/ml, respectively with a selectivity index of 44 against vero cells). Manilkara discolor also exhibited promising antiplasmodial activity especially against D6 (IC₅₀ 11.5 and 26.6 μg/ml). In addition, ethyl acetate extract of the roots of Pentas lanceolata and the aerial parts of Sericocomopsis hildebrandtii demonstrated moderate antiplasmodial activity against D6 and W2 (IC₅₀ 14.3 and 16.51 μg/ml) respectively. F. africana therefore has high potential and can be pursued for the development of an antimalarial drug.     

Antiplasmodial activity of targeted zinc(II)-dipicolylamine complexes

This study measured the antiplasmodial activity of nine zinc-dipicolylamine (ZnDPA) complexes against three strains of Plasmodium falciparum, the causative parasite of malaria. Growth inhibition assays showed significant activity against all tested strains, with 50% inhibitory concentrations between 5 and 600 nM and almost no toxic effect against host cells including healthy red blood cells. Fluorescence microscopy studies with a green-fluorescent ZnDPA probe showed selective targeting of infected red blood cells. The results suggest that ZnDPA coordination complexes are promising antiplasmodial agents with potential for targeted malaria treatment.     

Antiplasmodial activity of sesquilignans and sesquineolignans from Bonamia spectabilis

Phytochemical re-investigation of the aerial parts of Bonamia spectabilis (Convolvulaceae) led to the isolation of four minor tetrahydrofuran-type sesquilignans (bonaspectins E-H) together with the known neolignan virolongin A and the known lignan rel-(7S,8R,7'R,8'R)-3,3',4,4',5,5'-hexamethoxylignan. Their structures were established on the basis of spectral data. These six compounds as well as further seven lignanoids from B. spectabilis, characterised previously, were tested for their antiplasmodial activity against a chloroquine-sensitive strain (PoW) and a chloroquine-resistant clone (Dd2) of Plasmodium falciparum. Bonaspectin C 4"-O-glucoside, its aglycone, and bonaspectin D 4"-O-glucoside revealed the highest antiplasmodial activities (IC50 values: 1.3, 2.0, 6.5 microM [PoW]; 1.7, 4.6, 3.7 microM [Dd2], respectively).     

Antiplasmodial activity of (I-3,II-3)-biflavonoids and other constituents from Ormocarpum kirkii

Preliminary screening of a series of medicinal plants, traditionally used in Tanzania, showed an IC₅₀ of 15.6-31.2 μg/ml for the crude extract of the root of Ormocarpum kirkii S. Moore (Papilionaceae) against Plasmodium falciparum. A bioguided isolation was performed in order to isolate the active constituents. Twelve constituents were obtained and identified using NMR and MS data, and optical rotation measurements. The compounds comprised seven (I-3,II-3)-biflavonoids, three (I-3,II-3)-bi-4-phenyldihydrocoumarins, an isoflavanone and a C-glucosylated flavone. Six compounds, liquiritigeninyl-(I-3,II-3)-naringenin, apigeninyl-(I-3,II-3)-naringenin, 7-O-β-D-glucopyranosylchamaejasmin, (3R,4S,3″R,4″S)-5,5″-di-O-methyldiphysin, 7-O-β-D-glucopyranosyldiphysin, and 4″-hydroxydiphysolone, were isolated in addition to six known components. The compounds were evaluated for antimicrobial activity in a broad screening panel, including P. falciparum. Seven of these showed antiplasmodial activity; isochamaejasmin being the most active with an IC₅₀ of 7.3 ± 3.8 μM, but the selectivity was rather limited. Thus, these constituents may contribute, at least in part, to the antimalarial use of O. kirkii in traditional medicine.     

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

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