Secondary metabolites of Diaporthe cameroonensis, isolated from the Cameroonian medicinal plant Trema guineensis.

From a fresh root of Trema guineensis (Ulmaceae), endophytic fungi were isolated, among which a taxon belonging to the new species Diaporthe cameroonensis. This strain was fermented in shake flask batch cultures and the broth was extracted with ethyl acetate. From the crude extract, a hemiketal polyketide 1, and an acetylated alternariol 2 were isolated, along with fifteen known secondary metabolites. Their structures were established by extensive NMR spectroscopy and mass spectrometry analyses, as well as by comparison with literature data of their analogs.

Polyoxygenated Stigmastane-Type Steroids from Vernonia kotschyana Sch. Bip. ex Walp. and Their Chemophenetic Significance.

Four polyoxygenated stigmastanes (1-4) alongside known analogues (7-8) and flavonoids (5-6) were isolated from a dichloromethane/methanol (1:1, v/v) extract of the whole plant of Vernonia kotschyana Sch. Bip. ex Walp. (Asteraceae). Their structures were determined by means of spectroscopic and spectrometric analysis. The relative stereochemistry of the new compounds was established and confirmed via biosynthesis evidence and cyclization of 1 under acidic conditions. A plausible biosynthetic pathway to the new compounds and the chemophenetic significance of the isolated constituents were also discussed. The crude extract, fractions, and compounds (1-3) were assessed for their antibacterial activity against five highly prevalent bacterial strains. The fractions and compounds showed low to moderate activity with minimal inhibitory concentrations (MICs) > 125 µg/mL.

UPLC-QToF-ESI-MS identification and anthelmintic activity of Mitragyna inermis (Willd.) Kuntze (Rubiaceae).

Medicinal plants attract the attention of many researchers to find natural and safe remedies for various resistant diseases. Leaves of Mitragyna inermis are widely used in traditional veterinary medicine for the treatment of gastrointestinal strongyles of small ruminants. The aim of the current study is to estimate the antioxidant, anthelmintic and the larval toxicity of the aqueous and hydroethanolic extracts of this plant in addition to the hexane, dichloromethane and ethanol fractions of the hydroethanolic extract. Investigation of the most active extract using Ultra Performance Liquid Chromatography coupled with Quadrupole Time-of-Flight Electrospray Ionization Mass Spectrometry (UPLC-QToF-ESI-MS). Both plant extracts showed good antioxidant activity by scavenging the 2,2'-diphényl-1-picrylhydrazyl (DPPH) radical and reducing the ferric ion. Similarly, they were no-toxic to Artemia salina larvae (CL50 > 0.1 µg/mL). Also, they significantly reduced larval migration and motility of Haemonchus contortus adult worms (p < 0.001). The hexane, dichloromethane and ethanolic fractions of the hydroethanolic extract showed low activity compared to crude extracts except for the hexane fraction on H. contortus adult worms (p < 0.001) while it showed a poor result on larvae. It thus appears that the anthelmintic activity of the extract may be linked to the synergistic action of these compounds. The UPLC-QToF-ESI-MS analysis revealed the tentative identification of 15 compounds including 7 alkaloids. The results of the present study confirm the anthelmintic activity of M. inermis in traditional veterinary medicine.

Two new triterpenoid fatty acid esters from Schefflera barteri Harms (Araliaceae)§.

Two new fatty acid esters of triterpenoids (1-2) together with eleven known compounds (3-13) were obtained after investigation of the CH2Cl2-MeOH (1:1) crude extract from the leaves of Schefflera barteri Harms. All these compounds (1-13) were isolated for the first time from this plant among which compounds 3, 4, 6 and 9-13 were also isolated from the genus Schefflera for the first time. The structures of the isolated compounds were elucidated by analyses of their spectroscopic data (1D and 2D NMR, and MS). The antibacterial and cytotoxic activities of crude extracts, fractions and compounds (1, 2, 5, 6, 8 and 9) were investigated against both Gram-negative and Gram-positive bacteria strains as well as on human cervix carcinoma and colon adenocarcinoma cancer cell lines, respectively. They showed weak to significant activity towards the strains and malignant cells used.

Bio-guided isolation of anti-leishmanial natural products from Diospyros gracilescens L. (Ebenaceae).

BACKGROUND: Plants represent an intricate and innovative source for the discovery of novel therapeutic remedies for the management of infectious diseases. The current study aimed at discovering new inhibitors of Leishmania spp., using anti-leishmanial activity-guided investigation approach of extracts from Diospyros gracilescens Gürke (1911) (Ebenaceae), targeting the extracellular (promastigotes) and intracellular (amastigotes) forms of Leishmania donovani. METHODS: The plant extracts were prepared by maceration using H20: EtOH (30:70, v/v) and further fractionated using a bio-guided approach. Different concentrations of D. gracilescens extracts, fractions and isolated compounds were tested in triplicate against L. donovani promastigotes and amastigotes in vitro. The antileishmanial potency and cytotoxicity on RAW 264.7 cells were determined using the resazurin colorimetric assay. The time kill kinetic profile of the most active sample was also investigated. The structures of all compounds were elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR, and HR-ESI-MS and by comparison of their data with those reported in the literature. RESULTS: The hydroethanolic crude extract of D. gracilescens trunk showed the most potent antileishmanial activity (IC50 = 5.84 µg/mL). Further fractionation of this extract led to four (4) fractions of which, the hexane fraction showed the most potent activity (IC50 = 0.79 µg/mL), and seven (07) compounds that exhibited moderate potency (IC50 = 13.69-241.71 µM) against L. donovani. Compound 1-deoxyinositol (7) inhibited the promastigote and amastigote forms of L. donovani with IC50 values of 241.71 µM and 120 µM respectively and also showed the highest selectivity against L. donovani promastigotes (SI > 5.04). To the best of our knowledge, the antileishmanial activity of this compound is being reported here for the first time. The promising hexane fraction showed significant inhibition of parasites growth at different concentrations, but with no evidence of cidal effect over an exposure period of 120 h. CONCLUSIONS: The results obtained indicated that the hydroethanolic extract from the D. gracilescens trunk and the derived hexane fraction have very potent inhibitory effect on cultivated promastigotes and amastigotes of L. donovani parasite. The isolated compounds showed a lesser extent of potency and selectivity. However, further structure-activity-relationship studies of 1-deoxyinositol could lead to more potent and selective hit derivatives of interest for detailed drug discovery program against visceral leishmaniasis.

Antibacterial phloroglucinols derivatives from the leaves of Mallotus oppositifolius (Geisler) Müll. Arg. (Euphorbiaceae).

From the ethno-medicinally used leaves of Mallotus oppositifolius, four acylphloroglucinol derivatives, namely Acronyculatin SU (1-3) and Mallotojaponin D (4) were isolated along with seven known compounds (5-11). Structures were elucidated by comprehensive spectroscopic analyses and HRMS data. Absolute configurations were assigned by careful comparison of their specific optical rotation with those of closely related compounds. Compounds 1, 2, 6 and 11 demonstrated inhibitory activity against the bacterial strains E. coli, S. aureus, S. typhi, P. aeruginosa with minimum inhibitory concentration (MIC) values ranging from 3.125 to 50 µg/ml.

Ergostane-type steroids from the Cameroonian 'white tiama' Entandrophragma angolense.

Two new ergostane-type steroids named tiamenones A and B (1-2) were isolated from the bark of Entandrophragma angolense (Meliaceae) along with ten known compounds identified as 20S-hydroxy-4,6,24(28)-ergostatrien-3-one (3), 3ß,7α,20ß-trihydroxyergosta-5,24(28)-diene (4), 3ß,5α-dihydroxyergosta-7,22-diene (5), stigmasterol, ß-sitosterol, ß-amyrin, oleanolic acid, asperphenamate, sucrose and daucosterol. The structures of the isolated compounds have been established using NMR spectroscopic and mass spectrometric analyses. The assignment of relative and absolute configurations of compound 1 was achieved by a NOESY experiment and comparison of its NMR data with those of known compound reported in literature. Compounds 1-3, ß-amyrin and asperphenamate were evaluated for their antibacterial potencies against five bacterial model strains viz. Escherichia coli DSMZ 1058, Pseudomonas agarici DSMZ 11810, Bacillus subtilis DSMZ 704, Micrococcus luteus DMSZ 1605 and Staphylococcus warneri DSMZ 20036 and their cytotoxicity on two cell lines KB3-1 and HT-29. No potencies were exhibited by the tested compounds even at the highest concentration of 0.5 mg/mL. Compounds 1-3 were found to be potential HIV-1 inhibitors based on their molecular docking analyses.

seco-Tiaminic acids B and C: Identification of two novel 3,4-seco-tirucallane triterpenoids isolated from the root of Entandrophragma congoënse (Meliaceae).

Chemical investigation of the roots of Entandrophragma congoënse (Meliaceae) led to the isolation of two new 3,4-seco-tirucallane triterpenes, namely seco-tiaminic acids B and C (1 and 2) together with nine known compounds: 3,4-secotirucalla-21-formyl-23-oxo-4(28),7,24-trien-3-oic acid (3), methyl angolensate (4), molucensin N (5), molucensin O (6), piscidinol A (7), 7α,20(S)-dihydroxy-4,24(28)-ergostadien-3-one (8), 24-methylene-cholest-5-en-3ß,7α-diol (9), entilin A (10), and entilin B (11). Their structures were determined using extensive spectroscopic methods including 1D and 2D NMR, HRMS, and CD analyses; new results were compared to existing data in the literature. The two newly identified seco-tiaminic acids showed moderate antiplasmodial and cytotoxic activities against a chloroquine-sensitive strain of the malaria parasite (Plasmodium falciparum NF54) and were cytotoxic toward an L6 rat skeletal myoblast cell line, respectively.

Antiplasmodial and Cytotoxic Triterpenoids from the Bark of the Cameroonian Medicinal Plant Entandrophragma congoënse.

Eight new triterpenoids, prototiamins A-G (1-6, 9) and seco-tiaminic acid A (10), were isolated along with four known compounds from the bark of Entandrophragma congoënse. Their structures were elucidated by means of HRMS and different NMR techniques and chemical transformations. Assignments of relative and absolute configurations for the new compounds were achieved using NOESY experiments and by chemical modification including the advanced Mosher's method. Additionally, the structure and relative configuration of compound 3 were confirmed by single-crystal X-ray diffraction analysis. Compounds 1, 3, and 5 displayed significant in vitro antiplasmodial activity against the erythrocytic stages of chloroquine-sensitive Plasmodium falciparum strain NF54. Prototiamin C (3) was the most potent of the compounds isolated, with an IC50 value of 0.44 µM. All compounds tested showed low cytotoxicity for the L6 rat skeletal myoblast cell line.

Minor secondary metabolites from the bark of Entandrophragma congoënse (Meliaceae).

Two new tirucallane-type triterpenoids were isolated from the bark of Entandrophragma congoënse (Meliaceae) along with five known compounds gladoral A, bipendensin, 4-hydroxymethyl-3,5-dimethyldihydrofuran-2(3H)-one, scopoletin and 5,7-dimethoxy-6-hydroxycoumarin. Their structures were elucidated by means of spectroscopic analyses including 1D and 2D-NMR spectroscopy, high resolution mass spectrometric data as well as the comparison of data with those reported in the literature. The tested compounds (1-4) displayed moderated antiplasmodial activity against erythrocytic stages of chloroquine-resistant Plasmodium falciparum strain NF54 and low cytotoxicity on L6 cell lines. All the isolated compounds are reported for the first time from the genus Entandrophragma.

Tramadol--a true natural product?

We have independently investigated the source of tramadol, a synthetic analgesic largely used for treating moderate to severe pain in humans, recently found in the roots of the Cameroonian medicinal plant, Nauclea latifolia. We found tramadol and its three major mammalian metabolites (O-desmethyltramadol, N-desmethyltramadol, and 4-hydroxycyclohexyltramadol) in the roots of N. latifolia and five other plant species, and also in soil and local water bodies only in the Far North region of Cameroon. The off-label administration of tramadol to cattle in this region leads to cross-contamination of the soil and water through feces and urine containing parent tramadol as well as tramadol metabolites produced in the animals. These compounds can then be absorbed by the plant roots and also leached into the local water supplies. The presence of tramadol in roots is, thus, due to an anthropogenic contamination with the synthetic compound.

Indolosesquiterpene alkaloids from the Cameroonian medicinal plant Polyalthia oliveri (Annonaceae).

The stem bark of Polyalthia oliveri was screened for its chemical constituents using liquid chromatography high resolution mass spectrometry resulting in the isolation of three indolosesquiterpene alkaloids named 8α-polyveolinone (1), N-acetyl-8α-polyveolinone (2) and N-acetyl-polyveoline (3), together with three known compounds, dehydro-O-methylisopiline (4), N-methylurabaine (5) and polycarpol (6). The structures of the compounds were elucidated by means of high resolution mass spectrometry and different NMR techniques and chemical transformations. Their absolute configurations were assigned by ab-initio calculation of CD and ORD data (for 2 and 3) and X-ray diffraction analysis (for 2). Compounds 2 and 3 exhibited moderate antiplasmodial activity against erythrocytic stages of chloroquine-sensitive Plasmodium falciparum NF54 strain and low cytotoxicity on rat skeletal myoblast (L6) cell line.

Isolation and characterization of six labdane diterpenes and one pregnane steroid of Turraeanthus africanus.

Six labdane diterpene derivatives, named turraeanins F-J (3-6, 8) and epi-turraeanin J (7), and a pregnane steroid derivative named turraeasterodionene (2), were isolated by preparative high performance liquid chromatography together with thirteen known compounds from the Cameroonian medicinal plant Turraeanthus africanus. Their structures were elucidated by means of nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry in conjunction with the published data for the analogs, as well as the fragmentation patterns of each compound. Most of the known compounds were obtained for the first time from this plant. The compounds (2-7) were tested for their antibacterial efficacies against both Gram-positive and Gram-negative bacteria, including some clinically-important Risk group 2 human pathogens. Compound 4 exhibited the most pronounced antibacterial effectiveness comparable to standard reference streptomycin, with more potency against Gram-positive than Gram-negative bacteria. By comparing compounds 3, 4 and 5, a tentative structure-activity relationship could be drawn; selected oxidations at C-16 and C-18 drastically reduced the antibacterial efficacy of the parent compound (4). These results revealed the potential of compound 4 as a suitable antibacterial lead compound that might be used for further development of other derivatives to increase the antimicrobial efficacy.

Antiplasmodial and cytotoxic dibenzofurans from Preussia sp. harboured in Enantia chlorantha Oliv.

Two unusual dibenzofurans, preussiafurans A-B (1-2), together with six known compounds have been isolated from the fungus Preussia sp. occurring in Enantia chlorantha Oliv. The structures were established on the basis of 1D and 2D NMR spectroscopy and MS analysis. Compounds 1-4 showed antiplasmodial activity against erythrocytic stages of chloroquine-resistant Plasmodium falciparum (NF54) and moderate cytotoxicity on L6 cell lines with IC50 values of 8.67 and 14.8 µM, respectively.

Analgesic and antiinflammatory activities of the ethyl acetate fraction of Bidens pilosa (Asteraceae).

Bidens pilosa is an Asteraceae widely used in traditional medicine for the treatment of various ailments including pain and inflammation. The present work was undertaken to assess the analgesic and antiinflammatory properties of the ethyl acetate fraction of methylene chloride/methanol (1:1) extract of leaves of Bidens pilosa at the gradual doses of 50, 100 and 200 mg/kg in mice and rats, respectively. The analgesic properties of Bidens pilosa were investigated using the acetic acid writhing, hot plate, capsaicin and formalin-induced pain models. This was followed by a study of the antiinflammatory properties using carrageenan, dextran, histamine and serotonin to induce acute inflammation in rat hind paw. The extract provided a significant (p < 0.01) reduction in pain induced by all four models of nociception. It also presented significant (p < 0.05) antiinflammatory activity in all four models of acute inflammation. These results show that the ethyl acetate fraction of methylene chloride/methanol (1:1) of Bidens pilosa has both analgesic and antiinflammatory properties. The qualitative analysis of the fraction by the high-performance liquid chromatography (HPLC) fingerprint revealed the presence of two flavonoids, namely quercetin and iso-okanin, known to have antiinflammatory and antinociceptive properties, which could be responsible for the analgesic and antiinflammatory effects observed.

Monoterpenes with antibacterial activities from a Cameroonian medicinal plant Canthium Multiflorum (Rubiaceae).

Investigation of the crude extract obtained from the aerial parts of Canthium multiflorum led to the isolation of a new iridoid (1) together with twelve known compounds. The structures of these compounds were elucidated by interpretation of 1D and 2D NMR spectroscopic data, accurate mass measurements and comparison with analytical data of previously known analogues. Most of the isolated compounds have been reported for the first time from C. multiflorium. The antimicrobial activities of the isolated compounds were evaluated on five different bacterial strains using agar diffusion technique. The Gram-positive bacterium Staphylococcus aureus subsp. aureus (DSM 799), and the Gram-negative bacteria Actinobacter calco-aceticus (DSM 30006), Serratia plymuthica (DSM 4540), Pseudomonas stutzeri (DSM 4166) and Escherichia coli (DSM 1116) were employed for this purpose. The new iridoid, named 6-oxo-genipin (1), demonstrated significant inhibitory activity against all microbial strains tested, especially the pathogen Staphylococcus aureus. In addition, the compounds 3, 4 and 9 exhibited antiplasmodial activity against Plasmodium falciparum strain K1 and weak cytotoxicity against L6 cell lines.

Sapelenins G-J, acyclic triterpenoids with strong anti-inflammatory activities from the bark of the Cameroonian medicinal plant Entandrophragma cylindricum.

Four acyclic triterpene derivatives named sapelenins G-J (1-4), along with eight known compounds, sapelenins A-D, ekeberin D2 (5), (+)-catechin and epicatechin, and anderolide G, were isolated from the stem bark of the Cameroonian medicinal plant, Entandrophragma cylindricum Sprague, on the basis of bioassay-guided fractionation. Their structures were determined by means of high-resolution mass spectrometry and NMR spectroscopic data, as well as by comparison with the literature values of their analogs. The absolute configurations of the compounds (1-4) were assigned by the modified Mosher's method in conjunction with NOESY experiments and chemical modifications. The anti-inflammatory activities of the sapelenins were evaluated by assessing their ability to suppress or inhibit the secretion of cytokine interleukin-17 (IL-17) by human peripheral blood mononuclear cells (PBMC) stimulated with phytohemagglutinin (PHA). The cytotoxicity of these compounds on PMBCs was further assessed for correctly interpreting their anti-inflammatory responses. The tested compounds demonstrated moderate to significant anti-inflammatory activities by suppressing the secretion of IL-17 by PHA-stimulated human PBMCs. One of them, sapelenin G (1), showed high potency in suppressing the secretion of IL-17 by PBMCs comparable to reference cyclosporine A, without causing any cytotoxic effects (negligible), and deserves further considerations towards developing an effective anti-inflammatory drug.

Prenylated anthraquinones and other constituents from the seeds of Vismia laurentii.

Two new prenylated anthraquinones, laurenquinone A (1) and B (2) were isolated from the seeds of Vismia laurentii together with four known compounds; xanthone V(1) (3), physcion (4), 3-geranyloxyemodin anthrone (5) and friedelin (6). The structures of the new metabolites were determined with the help of spectroscopic data including extensive 2D-NMR spectroscopy. The known compounds were identified by comparison of their physical and spectroscopic data with those reported in the literature. Compounds 1, 4 and 5 exhibited moderate algicidal activity against Chlorella fusca and 3 showed moderate activity against the gram-positive bacterium Bacillus megaterium.