Alain François Kamdem Waffo

O-Prenylated Acridone Alkaloids from the Stems of Balsamocitrus paniculata (Rutaceae)

Two new O-prenylated acridone alkaloids, balsacridone A (1) and B (2), together with eighteen known compounds were isolated from the methanol extract from the stems of Balsamocitrus paniculata, a Cameroonian medicinal plant. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral (EI and ESI) data, and chemical reactions. N-methyl-6-methoxybenzoxazolinone (16) was isolated for the first time from a natural source while compounds 13, 14, and 15 for the first time from this genus. Pure compounds were tested for their activity against bacteria, fungi, and plant pathogen oomycetes, using the paper disk agar diffusion assay. The agar diffusion test delivered low to missing antimicrobial activities, corresponding to MICs > 1 mg/mL. However, compounds 1-15 exhibited a strong suppressive effect on phagocytosis response upon activation with serum opsonized zymosan in the range of IC50 = 0.5-7.2 μM, and the acridone alkaloids (1-5), N-trans-p-coumaroyltyramine (13), and N-trans-pcoumaroyloctopamine (14) displayed weak cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3, with IC₅₀ values ranging from 69.8 to 99.0 μM.

Oxidative burst inhibition, cytotoxicity and antibacterial acriquinoline alkaloids from Citrus reticulate (Blanco)

Two novel acridone-quinoline alkaloids, acriquinoline A (1) and acriquinoline B (2), together with twenty-two known compounds were isolated from the methanol extract of the root of Citrus reticulata Blanco. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR and mass spectral (EI and ESI) data. The possible biosynthesis for the formation of above compounds is proposed, based on close examination of their structures. Compounds 1, 2, 6, 10 and 14-17 exhibited strong suppressive effect on phagocytosis response upon activation with serum opsonized zymosan in the range of IC50 0.2-10.5μM, which was tested in vitro for oxidative burst studies of whole blood. However, compounds displayed low cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3, with IC50 between 30.8 and 60.5μM compared to the standard doxorubicin with IC50 0.9μM. These compounds, tested against bacteria, fungi and plant pathogen oomycetes by the paper disk agar diffusion assay, resulting in missing to low activities corresponding with MICs>1mg/mL.

Acridone alkaloids and coumarins from the stem bark of Citropsis articulata (Rutaceae).

A new acridone alkaloid, citropsine A (1), and thirteen known compounds (2 - 14) were isolated from the MeOH extract of the stem bark of Citropsis articulata. Structures of all compounds were determined by detailed analyses of their 1D and 2D NMR spectra, mass spectrometric data and by comparison with previously known analogs. Graphical Abstract Acridone Alkaloids and Coumarins from the Stem Bark of Citropsis articulata (Rutaceae)

Potent Antioxidant and Lipoxygenase Inhibitory Flavanone and Chalcone from Erythrina mildbraedii Harms (Fabaceae) of Cameroon

In continuation of our search for new secondary metabolites from African Erythrina species, E. mildbraedii of Cameroon was investigated. As a result of this study, a new flavanone (mildbone, 1) and a new chalcone (mildbenone, 2) have been obtained and characterized by spectroscopic means. Both the compounds exhibited significant antioxidant and moderate lipoxygenase inhibitory activities. Compounds 1 and 2 showed potent antioxidant activity even stronger than the positive control. Among both the compounds, mildbone (1) was found to be potent in both the assays. Graphical Abstract Potent Antioxidant and Lipoxygenase Inhibitory Flavanone and Chalcone from Erythrina mildbraedii Harms (Fabaceae) of Cameroon

Antimicrobial Furoquinoline Alkaloids from Vepris lecomteana (Pierre) Cheek & T. Heller (Rutaceae)

Three new prenylated furoquinoline alkaloids named lecomtequinoline A (1), B (2), and C (3), together with the known compounds anhydroevoxine (4), evoxine (5), dictamnine (6), N-methylflindersine (7), evoxanthine (8), hesperidin, lupeol, β-sitosterol, stigmasterol, β-sitosterol-3-O-β-d-glucopyranoside, stearic acid, and myristyl alcohol, were isolated by bioassay-guided fractionation of the methanolic extracts of leaves and stem of Vepris lecomteana. The structures of compounds were determined by spectroscopic methods (NMR, MS, UV, and IR) and by comparison with previously reported data. Crude extracts of leaves and stem displayed high antimicrobial activity, with Minimum Inhibitory Concentration (MIC) (values of 10.1–16.5 and 10.2–20.5 µg/mL, respectively, against Escherichia coli, Bacillus subtilis, Pseudomonas agarici, Micrococcus luteus, and Staphylococcus warneri, while compounds 1–6 showed values ranging from 11.1 to 18.7 µg/mL or were inactive, suggesting synergistic effect. The extracts may find application in crude drug preparations in Western Africa where Vepris lecomteana is endemic, subject to negative toxicity results in vivo.

Phytochemical and Antimicrobial Studies of Maprounea membranacea Pax & K. Hoffm (Euphorbiaceae)

The aim of the present study was to carry out the isolation, purification and structural identification of secondary metabolites from methanolic extract of stem bark of Maprounea membranacea and further to evaluate the antimicrobial activity of its fractions. According to the literature and due to their use in traditional medicine, plants of the genus Maprounea may be good candidate for new antimicrobial drugs. In this study, the air-dried and powdered stem bark (6.3 kg) of M. membranacea Original Research Article Ekon et al.; AJOCS, 3(1): 1-8, 2017; Article no.AJOCS.35033 2 was extracted 02 times by percolation with methanol (MeOH) for 48 h. A part of this residue (350 g) was suspended in distilled water and partitioned successively between hexane and ethyl acetate (EtOAc) to obtain hexane, ethyl acetate and water soluble fractions. The two first fractions were then subjected to repeated column chromatographic separation. The structures of the isolates were established by means of spectroscopic methods. The crude extract and its fractions were also screened in vitro for their activity against bacteria and fungi. Eight known compounds including friedelin, betulinic acid, lupeol, epigallocatechin, β-sitosterol, β-sitosterol glucoside, stigmasterol and stigmasterol glucoside were isolated from hexane and ethyl acetate fractions of methanolic extract of stem bark. The structures of these compounds were determined by comprehensive spectroscopic analyses (1D, 2D NMR) and by comparison of their data with those reported in the literature. The agar diffusion test resulted in low to missing antibacterial activities. In addition, all fractions and crude extract displayed significant antifungal activities with MIC value ranging from 1.25-40.0 μg/μl.

A prenylated acridone alkaloid and ferulate xanthone from barks of Citrus medica (Rutaceae)

Abstract A new prenylated acridone alkaloid, medicacridone (1), and a new ferulate xanthone, medicaxanthone (5), together with 11 known compounds were isolated from the methanol extract of the bark of the Cameroonian medicinal plant Citrus medica. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral (EI and ESI) data, chemical reactions, and comparison with previously known analogues. The agar diffusion test delivered low to missing antimicrobial activities, corresponding with MICs > 1 mg mL–1, while compounds 1–6 and atalantoflavone (9) displayed weak cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3, with IC50 values ranging from 60.5 to 80.0 μm versus doxorubicine with IC50=0.9 μm.