Efficacité in vitro et in vivo des extraits de plantes contre le mildiou (Phytophthora infestans) de la morelle noire

La lutte contre les maladies des plantes par l’utilisation des fongicides de synthèse, lorsqu’ils sont appliqués sur les fruits et légumes pose le plus souvent de problèmes de toxicité aux consommateurs. La présente étude a pour objectif de tester l’efficacité in vitro et in vivo des extraits de plantes (substances naturelles) contre le mildiou de la morelle noire, un légume très consommé dans la sous-région Afrique centrale. L’évaluation de l’activité antifongique des extraits de plantes a été faite par la méthode de dispersion sur milieu gélosé. Les concentrations équivalentes pour l’inhibition de 50% et 90% de la croissance du pathogène (CE50 et CE90), les concentrations minimales inhibitrices (CMI), et les aires standardisées sous la courbe de progression de la maladie (ASSCPM) ont été utilisées pour évaluer l’efficacité des extraits. L’extrait à l’acétone des feuilles de Syzygium aromaticum a donné la CMI la plus faible (60 μg/ml). Aucune différence significative n’a été observée entre l’extrait de Callistemon viminalis (ASSCPM=11,5%) et le manèbe (ASSCPM=7,3%). L’extrait de S. aromaticum a perdu son efficacité in vivo. L’étude montre que l’extrait de C. viminalis peut davantage être étudié pour ses propriétés antifongiques dans un programme de lutte contre le mildiou.Mots clés: substance naturelle, contrôle du mildiou, Phytophthora infestans, Solanum scabru

Potential of essential oils from four Cameroonian aromatic plants used in integrated protection of stored products programs: Presentation

The efficacy of essential oils extracted from fruits of Piper capense and Xylopia parviflora, and roots of Echinops giganteus and Mondia whitei were evaluated against Acanthoscelides obtectus and fungi isolated from bean seeds in laboratory conditions in Cameroon. The essential oils were extracted by water-distillation and their chemical composition identified by Gas Chromatography-Flame Ionization Detection (GC-FID) and Gas Chromatography- Mass Spectrometry (GC-MS). Toxicity assays of essential oils against A. obtectus were carried out by fumigation in which insect pests were exposed fumes of the essential oils, and mortality recorded after 6, 12, and 24 hours. Additionally, the toxicity by contact of the essential oils was evaluated through coating grains with essential oils or impregnating the essential oils onto the filter paper, allowing the insects to physically get in contact with the essential oil, and assessing weevil mortality recorded after 1, 2, 3, and 4 days. The essential oils from P. capense and X. parviflora consisted mainly of hydrocarbon monoterpenes (56.5% and 50.0% respectively), whereas the essential oils from E. giganteus was mostly constituted of sesquiterpenes (94.3%) in which the tricyclic compounds are more abundant. A major compound identified in the essential oil from M. whitei was 2-hydroxy- 4-methoxy-benzaldehyde (81%). The essential oil from X. parviflora was the most effective as contact and fumigant against A. obtectus, causing 100% mortality within 1 day at low lethal concentrations. On the other hand, the essential oil from M. whitei exhibited the best anti-fungal activity. These essential oils could play an important role in pest protection of stored beans and reduce the risks associated with use of synthetic insecticides especially in low income small holder farming systems.The efficacy of essential oils extracted from fruits of Piper capense and Xylopia parviflora, and roots of Echinops giganteus and Mondia whitei were evaluated against Acanthoscelides obtectus and fungi isolated from bean seeds in laboratory conditions in Cameroon. The essential oils were extracted by water-distillation and their chemical composition identified by Gas Chromatography-Flame Ionization Detection (GC-FID) and Gas Chromatography- Mass Spectrometry (GC-MS). Toxicity assays of essential oils against A. obtectus were carried out by fumigation in which insect pests were exposed fumes of the essential oils, and mortality recorded after 6, 12, and 24 hours. Additionally, the toxicity by contact of the essential oils was evaluated through coating grains with essential oils or impregnating the essential oils onto the filter paper, allowing the insects to physically get in contact with the essential oil, and assessing weevil mortality recorded after 1, 2, 3, and 4 days. The essential oils from P. capense and X. parviflora consisted mainly of hydrocarbon monoterpenes (56.5% and 50.0% respectively), whereas the essential oils from E. giganteus was mostly constituted of sesquiterpenes (94.3%) in which the tricyclic compounds are more abundant. A major compound identified in the essential oil from M. whitei was 2-hydroxy- 4-methoxy-benzaldehyde (81%). The essential oil from X. parviflora was the most effective as contact and fumigant against A. obtectus, causing 100% mortality within 1 day at low lethal concentrations. On the other hand, the essential oil from M. whitei exhibited the best anti-fungal activity. These essential oils could play an important role in pest protection of stored beans and reduce the risks associated with use of synthetic insecticides especially in low income small holder farming systems

Insecticidal effect of anisaldehyde against Acanthoscelides obtectus and Callosobruchus maculatus (Coleoptera: Bruchidae)

In the present study, anisaldehyde, a compound found in the essential oil of Clausena anisum-olens, was tested for its insecticidal activities against Acanthoscelides obtectus and Callosobruchus maculatus. The amounts of anisaldehyde applied were 0, 0.5, 1, 2 and 4 μL diluted in 1mL of acetone and applied to 40 g of either beans or cowpeas corresponding to the doses of 0, 0.008, 0.016, 0.033 and 0.066 μL/g of seed. Additionally, adsorbent clay was used as a carrier of this product in order to increase the persistence of its insecticidal activity over time. This clay was mixed with the aforementioned volumes of anisaldehyde to form a powder formulation. Furthermore, to assess the insecticidal effect over time, the F1 progeny production was also evaluated. These two products caused significant mortality in the two tested insects. Nevertheless, C. maculatus was more susceptible than A. obtectus at tested doses. The progeny production decreased with the increasing doses of anisaldehyde and ACP with 0 % at the highest dose (0.066 μL/g). According to the LD50, LD95 and their confidence intervals, the toxicity of ACP was significantly different (P < 0.05) to anisaldehyde at the tested doses towards A. obtectus adults. However, there was no significant difference observed between the effects of these two products towards C. maculatus. These preliminary results suggest that anisaldehyde and ACP could be used in stored-product protection, but this needs further research. Research is also needed to determine its toxicity on rats in order to assess its potential hazards for workers and consumers.Keywords: Anisaldehyde, Clay, Contact toxicity, Bruchid

Isolation and caracterisation of sodium monocarboxylate ixoside salt from the stem bark of Oxyanthus pallidus

A sodium monocarboxylate ixoside salt(1) and four known compounds, ixoside (2), mannitol (3), uncargenine C (4) and oleanolic acid (5) have been isolated from the stem bark of Oxyanthus pallidus. Their structures were established on the basis of spectroscopic techniques.Keywords: Oxyanthus pallidus, Oxyanthus sankuruensis, Oxyanthus schubotzianus, Rubiaceae, iridoids, sodium monocarboxylate ixoside salt

Antisalmonellal Activities of Extracts, Fractions, Compounds and Semi-synthetic Flavonoid Derivatives from Tristemma hirtum P. Beauv (Melastomataceae)

The development and spread of resistance to currently available antibiotics is a major drawback in the treatment of microbial infections. Salmonellosis for example remains among the most common cause of morbidity and mortality in developing countries. This study aimed to evaluate the antisalmonellal potential of extracts, fractions, isolated compounds and semi-synthetic flavonoids from Tristemma hirtum P. Beauv. Bioguided fractionation by column chromatography of the EtOAc and n-BuOH fractions led to the isolation of eleven compounds including two new esterified glucuronide flavonoids namely: luteolin-3′-O-β-D-glucuronopyranosylbutyl ester (1), a mixture of compound 1 and quercetin-3-O-β-D-glucuronopyranosylbutyl ester (2). Chemical transformation mainly based on the prenylation of 6-hydroxyapigenin-7-O-β-D-glucopyranoside (5) afforded four new semi-synthetic flavonoid derivatives namely: 6, 4'-O-diprenylapigenin-7-O-β-D-glucopyranoside (5a), 8-Cprenyl- 6, 4'-O-diprenylapigenin-7-O-β-D-glucopyranoside (5b), 8-C-prenyl-4'-O-prenylapigenin-7-O-β-D-glucopyranoside (5c), 4'-O-prenylapigenin-7-O-β-D-glucopyranoside (5d). The chemical structures of these compounds were assigned using NMR techniques, mass spectrometry and by comparison of their data with reported ones. The antisalmonellal activity was assessed by determining the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) using serial microdilution methods. The results showed that the MeOH extract and EtOAc fraction were active against all the bacteria tested with MICs ranging from 24 to 1536 μg/mL. Seven isolated compounds and three semi-synthetic compounds tested showed MIC values ranging from 16 to 256 μg/mL. Compounds 1, 3, 5a, 5c and 11 displayed the most potent antisalmonellal properties but were generally less potent than those of reference drugs. The activity of extracts and isolated compounds could be used as the starting point for the development of alternative phytodrugs against salmonellosi

Analgesic and Anti-Inflammatory Properties of Extracts from the Bulbils of Dioscorea bulbifera L. var sativa (Dioscoreaceae) in Mice and Rats

The aqueous and methanol extracts from the dry bulbils of Dioscorea bulbifera L. var sativa (Dioscoreaceae)—evaluated orally at the doses of 300 and 600 mg/kg against pain induced by acetic acid, formalin, pressure and against inflammation induced by carrageenan, histamine, serotonin and formalin in mice and rats, showed a dose dependant inhibition of pain and inflammation with a maximum effect of 56.38%, 73.06% and 42.79% produced by the aqueous extract, respectively on pain induced by acetic acid, formalin and pressure while the methanol extract at the same dose respectively inhibited these models of pain by 62.70%, 84.54% and 47.70%. The oral administration of aqueous and methanol extracts caused significant anti-inflammatory activity on paw oedema induced by histamine, serotonin and formalin. The present results show that the bulbils of Dioscorea bulbifera var sativa possess potent analgesic and anti-inflammatory activities. These activities may results from the inhibition of inflammatory mediators such as histamine, serotonin and prostaglandins. Thus, the analgesic activity of the bulbils of Dioscorea bulbifera may be at least partially linked to its anti-inflammatory activity

Antioxidant Activities and Chemical Constituents of Extracts from Cordyline fruticosa (L.) A. Chev. (Agavaceae) and Eriobotrya japonica (Thunb) Lindl, (Rosaceae)

Background and Objective: Cordyline fruticosa (Agavaceae) and Eriobotrya japonica (Rosaceae) are two medicinal plants used for the treatment of various diseases such as infections of mammary glands, sore throat and neck pain for the first plant, diabetes, cough, ulcers, protection against oxidative stress and cognitive deficits for the latter. The present study was designed to evaluate the antioxidant activity of the different extracts of these two plants as well as to isolate and identify their chemical constituents. Materials and Methods: The plant extract was prepared by maceration in methanol, compounds were isolated from EtOAc and n-BuOH extracts of the two plants using column chromatography and their structures were determined by means of NMR and MS analysis as well as in comparison with published data. Antioxidant tests (DPPH, ferric reduction antioxidant power and anti-hemolytic) were performed over the MeOH, EtOAc and n-BuOH extracts of the plants. Results: The antioxidant-guided phytochemical investigation of the MeOH extracts of the two plants led to the isolation of twelve compounds identified as: Farrerol 1, quercetin helichrysoside 2, apigenin 8-C-β-D-glucopyranoside 3, isoquercitrin 4 and rutin 5 from C. fruticosa, β-sitosterol 6, catechin 7, oleanolic acid 8, lyoniresinol 9, cinchonain IIb 10, lyoniresinol 2-a-O-β-D-xylopyranoside 11 and β-sitosterol-3-O-β-D-glucopyranoside 12 from E. japonica. Amongst the isolated compounds, the most important antioxidant ones were identified as helichrysoside and rutin from C. fruticosa, catechin, cinchonain IIb, lyoniresinol 2-a-O-β-D-xylopyranoside from E. japonica with EC50 of 8.73, 9.91, 4.11, 3.14 and 10.61 μg mL–1, respectively. Conclusion: Based on the obtained results, it can be concluded that the high ability to scavenge free radicals, reducing power of Fe3+ and hemolysis activity exerted by extracts of C. fruticosa and E. japonica were due to their high content of phenolic compounds, thus the structure-activity relationships of the isolated flavonoids were discussed. The results of this study suggest that the extracts from these two plants could serve as potential source of antioxidant compound

Amphibia, Bufonidae, Didynamipus sjostedti Andersson, 1903: new records and a review of geographic distribution

Didynamipus sjostedti is reported from two new sites in southwest Cameroon. The distribution of this species is discussed with a review of known specimen

Antimicrobial, antioxidant, anti-inflammatory activities and phytoconstituents of extracts from the roots of Dissotis thollonii Cogn. (Melastomataceae)

Abstract Background Dissotis thollonii Cogn. belonging to the Malastomataceae family is used in the West Region of Cameroon for the treatment of inflammation, kidney diseases, pregnancy control and sinusitis. Despite the traditional use of this plant, no scientific report or information was found in the literature regarding neither its biological activity nor its chemical constituents. Aim of the study The present work was designed to determine the antimicrobial, antioxidant and anti-inflammatory activities of different extracts of the roots of D. thollonii Cogn. as well as the isolation and identification of the chemical constituents of this plant. Materials and methods The tests for antimicrobial, antioxidant and anti-inflammatory activities were performed over the MeOH, EtOAc, n-BuOH and aqueous extracts. Compounds were isolated from EtOAc and n-BuOH extracts of the roots of D. thollonii Cogn. through column chromatography and their structures were determined by means of NMR and MS analysis, and published data. Results According to the antimicrobial and antioxidant assays, the EtOAc and n-BuOH extracts were submitted to further separation and purification. This led to the isolation of twelve compounds identified as 3,3′-di- O -methylellagic acid 4′- O-β -D-xylopyranoside 1 , 3- O -methylellagic acid 4′- O-β -D-arabinopyranoside 2 , casuarinin 3 , betulinic acid 4 , β -sitosterol-3- O -D-glucopyranosyl-6′-mirystate 5 , cellobiosylsterol 6 , β -sitosterol 7 , β -sitosterol-3- O-β -D-glucopyranoside 8, arjunolic acid 9 , 3,3′-di- O -methylellagic acid 10 , ellagic acid 11 , and 3,3′-di- O -methylellagic acid 4′- O - β -D-glucopyranoside 12 . The EtOAc extract was the only antimicrobial active sample [diameter of the zone of inhibition (DZI) of 10 mm against Staphyloccocus aureus ] among all the tested extracts. The analysis of fractions of this extract revealed the presence of bioactive compounds with a described antimicrobial activity such as β -sitosterol, β -sitosterol-3- O-β -D-glucopyranoside and arjunolic acid. By using Trolox as the standard drug, all extracts showed antioxidant activity against DPPH in the following order of scavenging ability: Trolox > nBuOH > EtOAc > MeOH > WE (water extract). The ABTS •+ scavenging ability was similar to that found for the DPPH assay, being Trolox > n-BuOH > MeOH > EtOAc > WE. Along with the DPPH and ABTS assays, the FRAP assay showed the scale n-BuOH > MeOH > WE > EtOAc. The phytochemical study of the EtOAc and n-BuOH extracts revealed the presence of important known antioxidant compounds such as ellagic acid derivatives, arjunolic acid, betulinic acid and β -sitosterol. The anti-inflammatory properties of D. thollonii extracts were investigated using RAW 264.7 murine macrophage cells. The MeOH extract reduced the stimulated NO production in a concentration-dependent manner. 86% reduction was observed at the highest tested concentration of 100 μg/ml (IC 50 = 5.9 μg/ml). The n-BuOH extract showed higher dose dependent reduction of NO formation (IC 50 = 6.5 μg/ml) than the EtOAc extract (IC 50 = 18.1 μg/ml), whereas the water extract had no significant influence on the NO production. All the extracts did not have any influence on the macrophage viability. The phytochemical investigation of the EtOAc and n-BuOH extracts revealed that the main compounds identified do have potent anti-inflammatory properties. Conclusion The biological and phytochemical characterization of the root extracts of D. thollonii validates the use of this plant for the treatment of inflammation and sinusitis, thus providing evidence that this plant extracts, as well as some of the isolated compounds, might be potential sources of antioxidant and anti-inflammatory drugs

ANTIMICROBIAL DITERPENOID ALKALOIDS FROM ERYTHROPHLEUM SUAVEOLENS (GUILL. & PERR.) BRENAN

An investigation of the stem bark of Erythrophleum suaveolens (Guill. & Perr.) Brenan yielded the known amide norcassaide (1) and a new diterpenoid alkaloid named norerythrosuaveolide (2) which was characterized as 7β-hydroxy-7-deoxo-6-oxonorcassaide. The structures were established on the basis of one and two-dimensional 1H and 13C NMR spectral data. The compounds showed potent antimicrobial activities against bacteria and yeasts. KEY WORDS: Erythrophleum suaveolens (Guill. & Perr.) Brenan, Norcassaide, Diterpenoid alkaloid, Norerythrosuaveolide, Antimicrobial activities, Bacteria, Yeasts Bull. Chem. Soc. Ethiop. 2005, 19(2), 221-226