Pierre Mkounga

In the title salt, C₇H₆N₃O₂S⁺·C₇H₅O₆S⁻, the cation is protonated at the thiazole N atom and the dihedral angle between the nitro group and its attached benzene ring is 3.6 (4)°. In the anion, the sulfonate group is deprotonated and the dihedral angle between the carboxylic acid grouping and its attached ring is 7.1 (4)° and an intramolecular O—H...O hydrogen bond occurs. In the crystal, cation-to-anion N—H...O and anion-to-anion O—H...O hydrogen bonds link the component ions into (101) sheets. Aromatic π–π stacking and weak C—H...O and C—H...S interactions also occur.

A series of known tetrazine derivatives, containing benzothiazole scaffold, were prepared during the coupling reactions of selected diazotized 2-aminobenzo[d]thiazole derivatives with p-acetaminophen. The as-prepared compounds were characterized based on NMR and MS spectrometry. The antibacterial and anti-biofilm activities of the synthesized compounds were evaluated by microdilution method, whereas the anti-quorum sensing effect was carried out using assay for the inhibition of violacein formation. As a result, compounds 4a, 4b and 4c revealed minimum inhibitory concentrations and minimum bactericidal concentrations ranging from 8 to 128 µg/mL and from 32 to 256 µg/mL, respectively. Compounds 4a (52-86.5%), 4b (57.7-79.4%) and 4c (59.9-80.3%) prevented biofilm formation in all the four bacteria tested with percentages of inhibition more than 50%. The concentrations of 4a, 4b and 4c that inhibited 50% of violacein production were found to be 62.71, 28.56 and 107.45 µg/mL, respectively, thus attesting that these compounds possess anti-quorum sensing activity. Noteworthy, our previous investigation attested that these compounds are non-cytotoxic on the human mammalian cells Vero. This novel contribution demonstrates the antibacterial, antibiofilm and anti-quorum sensing activities of tetrazine-based benzothiazoles, which might be prospected as scaffolds for the discovery of efficient antibiotics with decreased risk of microbial drug resistance.

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Diarrhea remains one of the leading causes of mortality worldwide, especially among children. Accumulated evidence has shown that Shigella species are the most prevalent bacteria responsible for diarrhea in developing countries. Antimicrobial therapy is necessary for Shigella infections; however, the development of resistance against current drugs justifies the pressing need to search for alternative medications. In this study, we have applied antibacterial phenotypic screening to identify potent anti-Shigella compounds across a broad chemical diversity, including selected acetaminophen derivatives containing a benzothiazole backbone, and their combination with certain antibiotics. As a result, two acetaminophen derivatives containing a benzothiazole backbone (4a and 4b) inhibited the growth of Shigella flexneri with a common MIC value of 12.5 µg/mL. These compounds were established through a time-kill kinetics study to be potentially bactericidal. Meanwhile, the 2-aminobenzothiazoles (1a and 1b) used for the synthesis of compounds 4 (a and b) were found to be poorly active (MIC: 100 µg/mL) against this pathogen. Combination studies of 4a and 4b with the least effective antibiotics (ceftriaxone and cotrimoxazole) demonstrated synergistic anti-Shigella activity with MIC values decreasing from 12.5 to 0.781 μg/ mL. The present study demonstrates that the azobenzothiazole dyes 4 (a and b) can be repurposed as potential anti-Shigella compounds, thus providing potential chemical pharmacophores for the discovery of drugs against infectious diarrhea caused by Shigella and other enteric pathogens, especially in developing countries.

Phytochemical investigation of the methanol extract from the fruits of Macaranga monandra (Euphorbiaceae Muell. et Arg.) afforded one new geranylated 1’,2’‐dihydrophenanthrene and two new flavonoid derivatives, named macamondrin (1), macamondrione A (2) and B (3) respectively. The structures of these compounds were elucidated mainly by NMR, mass spectral data and in comparison with data from the literature. Along with compounds 1–3, nine known compounds among which oleanolic acid (4); daucosterol (5); 3β‐acetoxy‐11α,12α‐epoxytaraxerol (6); 3,3’,4‐tri‐O‐methylellagic acid (7); 3,3’,4,4’‐tetra‐O‐methylellagic acid (8); 4’‐O‐methyl‐6‐isoprenylapigenin (9); 4’‐O‐methyl‐8 isoprenylkaempférol (10); 4’‐O‐methyl‐6‐isoprénylkaempférol (11); 6‐isoprénylkaempférol (12), were also isolated. Crude extracts as well as isolated compounds were evaluated for their antioxidant activity using the ABTS, DPPH and FRAP methods. It appears that the 50 % radical scavenging concentrations ranging from 6.26 to 11.7 μg/ml on the ABTS radical, from 1.77 to 48.22 μg/ml on the DPPH radical, and from 1.54 to 67.97 μg/ml with the FRAP method. For the compounds tested, very good antioxidant activities were observed, which clearly shows that these molecules can have an anti oxidative stress potentiel.

Diarrhea remains one of the leading causes of mortality worldwide, especially among children. Recent epidemiological studies conducted in developing countries identified Shigella species as the most predominant pathogenic bacteria responsible for diarrhea. Antimicrobial therapy is necessary for Shigella infections; however, the rapid emergence of resistance against existing antimicrobials in Shigella spp. poses a serious global health problem. To identify alternative antimicrobial compounds with activity against Shigella species, the pathogens responsible for bacterial diarrhea. In this study, we have applied antibacterial phenotypic screening to identify potent anti-Shigella compounds across a broad chemical diversity, including selected acetaminophen derivatives containing benzothiazoles backbone, and their combination with certain antibiotics. In continuation to our effort in searching potent antimicrobial compounds, we have found this time around that two acetaminophen derivatives containing benzothiazoles backbone (4a and 4b) could inhibit the growth of Shigella flexneri with common MIC value of 12.5 µg/ml. These compounds were established through a time-kill kinetics’ study to be bactericidal. Meanwhile, the 2-aminobenzothiazoles (1a and 1b) used for the synthesis of compounds 4 (a & b) were found to be poorly active (MIC: 100 µg/ml) against this pathogen. Combination studies of 4a and 4b with the least susceptible antibiotics (ceftriaxone and cotrimoxazole) demonstrated synergistic anti-Shigella activity. The present study demonstrates that the azobenzothiazole dyes 4 (a & b) can be repurposed as potential anti-Shigella compounds, which can serve as scaffolds for the development of new agents against infectious diarrhea caused by Shigella and other enteric pathogens, especially in developing countries.

The aim of this study was to describe the wood treatment sector in the cities of Douala and Yaoundé (Cameroon). A total of 319 semi-structured interviews were conducted. The respondents were agents of wood depots, sawmills, hardware stores, and carpentry shops. They were asked about the diversity of products used and their perception of the risks and dangers of treatments. The chemical method (40.4%) was the main means of preserving wood against termite attack according to the respondents, followed by the traditional method with 9.4%, the physical method (2.2%) and more rarely, the use of plant extract (0.3%). All the chemicals were found to be hazardous to the environment and human health, with Xylamon being classified as the most hazardous. The physical control methods and those using plant extracts were found to be not at all dangerous for human health and the environment. Notwithstanding concerns for the protection of the environment and human health, toxic and hazardous products are still predominantly used. It would be important to move towards less or non-toxic products.

Despite the medicinal uses of Phragmanthera capitata, Globimetula dinklagei and Tapinanthus bangwensis against memory loss, convulsions and pain, their efficacy against brain-dysfunction diseases and inflammation models has not yet been studied. Therefore, this study aims to investigate the anti-inflammatory and acetylcholinesterase (AChE) inhibitory potentials of their crude extracts and isolated natural compounds by combining in vitro and in silico experiments. Crude extracts and isolated compounds were tested in vitro for their AChE inhibitory activity by using Ellman’s method. Additionally, their anti-inflammatory activity was determined by evaluating the nitric oxide (NO) production inhibitory activity in lipopolysaccharide-stimulated RAW 264.7 macrophage cells and the 15-lipoxygenase (15-LOX) inhibitory activity by using the ferrous oxidation xylenol orange assay. Furthermore, the in silico efficacy of natural compounds was investigated against ten putative target enzymes relevant in Alzheimer’s disease (AD) pathogenesis and inflammation. It was found that the crude extracts had weak to moderate inhibitory potential against AChE, with the extract of T. bangwensis being the most active (50% inhibitory concentration (IC₅₀) = 48.97 µg/mL). Six natural compounds, namely, 3-O-β-D-glucopyranosyl-28-hydroxy-α-amyrin (2), apigenin- 8-C-β-D-glucopyranoside (3), globimetulin B (5), globimetulin C (6), bangwaursene B (8) and 3β-acetoxy-11,12-epoxytaraxerol (9), were identified for the first time as having anti-AChE potential, among which (9) had the highest efficacy with an IC₅₀ of 13.89 µM. Among the anti-AChE compounds, (5) was also efficient against NO production and 15-LOX, and the data are in agreement with the docking score. In summary, compounds (5) and (9) are the most prominent lead compounds that should be further tested experimentally against molecular targets of AD and inflammation.

The bio guided fractionation of the dichloromethane/methanol (1:1) crude extract of the air-dried whole plant of C. aegyptiaca led to the isolation of one new flavone derivative designated conyflavone (1) and one new clerodane diterpene type designated conyclerodane (2) along with five known compounds including two flavonoids Gardenin C (3), chrysosplenetin (4) and two steroids glucoside of β-sitosterol (5), the mixture of stigmasterol (6) and β-sitosterol (6′) and ent-2b,18,19trihydroxycleroda-3,13-dien-16,15-olide (7). The structures were established by spectroscopic methods including IR, 1D and 2D NMR in conjunction with mass spectroscopy and by comparison to data of related compounds described in literature. The stereocentres in compound 2 were determined by SC-XRD analysis. Crude extract as well as fractions and pure compounds were evaluated in vitro for their antibacterial activities against four pathogenic and two clinical isolate strains using microdilution methods. Extracts and compounds displayed a moderate antibacterial activity with MIC values ranging from 125 to 500 µg/mL. Graphical Abstract