Antimicrobial and antileishmanial xanthones from the stem bark of Allanblackia gabonensis

Evolution of Acridines and Xanthenes as a Core Structure for the Development of Antileishmanial Agents

Nowadays, leishmaniasis constitutes a public health issue in more than 88 countries, affecting mainly people from the tropics, subtropics, and the Mediterranean area. Every year, the prevalence of this infectious disease increases, with the appearance of 1.5–2 million new cases of cutaneous leishmaniasis and 500,000 cases of visceral leishmaniasis, endangering approximately 350 million people worldwide. Therefore, the absence of a vaccine or effective treatment makes the discovery and development of new antileishmanial therapies one of the focuses for the scientific community that, in association with WHO, hopes to eradicate this disease shortly. This paper is intended to highlight the relevance of nitrogen- and oxygen-containing tricyclic heterocycles, particularly acridine and xanthene derivatives, for the development of treatments against leishmaniasis. Thus, in this review, a thorough compilation of the most promising antileishmanial acridine and xanthene derivatives is performed from both natural and synthetic origins. Additionally, some structure–activity relationship studies are also depicted and discussed to provide insight into the optimal structural features responsible for these compounds’ antileishmanial activity.

Antileishmanial, antibacterial and cytotoxicity activity of the extracts, fractions, and compounds from the fruits and stem bark extracts of Pentadesma butyracea Sabine

The search for antileishmanial plants used in traditional medicine led to the choice of CH2Cl2–MeOH (1:1) crude extract of the fruits and stem bark of Pentadesma butyracea Sabine (Clusiaceae) which displayed good activity in vitro against Leishmania donovani 1S (MHOM/SD/62/1S) promastigotes during preliminary screening with IC50 values 5.96 and 26.43 μg mL−1, respectively. The fractionation of both extracts using flash chromatography yielded active fractions with IC50 values ranging from 2.71 to 18.88 μg mL−1. Fourteen compounds (1–14) were isolated from the obtained fractions using successive column chromatographies and their structures were elucidated based on the analysis of their NMR and MS data. Daphnifolin (1), epicathechin (3), α-mangostin (9) and 9-hydroxycalabaxanthone (14) exhibited potent antileismanial activity against L. donovani 1S (MHOM/SD/62/1S) promastigotes with IC50 values of 2.01, 9.09, 3.37, and 6.87 μg mL−1, respectively and good selectivity towards Raw 264.7 macrophage cells (SI > 2.4). Extracts, fractions and some isolates were also assessed in vitro for their antibacterial activity against six bacterial strains [Salmonella typhi (CPC), Enterobacter cloacae (CPC), Pseudomonas aeruginosa HM801, Staphylococcus aureus ATCC 43300, Streptococcus pneumoniae ATCC 491619, Escherichia coli ATCC 25322] using serial microdilution method. Among the tested samples, the stem bark extract of P. butyracea as well as compounds 2 and 8 showed good to moderate activity against the aforementioned bacterial strains with MIC ≤ 250 μg mL−1.

Structural Revision of Guttiferone F and 30-epi-Cambogin

Guttiferone F, a natural polyprenylated polycyclic acylphloroglucinol, was originally assigned as the 30-epimer of garcinol by NMR data analyses. Conversion of guttiferone F in the presence of acid afforded its cyclized form (2a), which was previously assigned as 30-epi-cambogin. However, the absolute configurations of guttiferone F and 2a have not been determined. Reinvestigation of the structures of those two compounds, using X-ray and NMR data analyses and chemical transformation, revealed that the original assignment of the C-30 absolute configuration in guttiferone F and 2a should be inverted. Guttiferone F is indeed garcinol, and 2a, which was previously identified as 30-epi-cambogin, is cambogin.

Chemical and Biological Research on Herbal Medicines Rich in Xanthones

Xanthones, as some of the most active components and widely distributed in various herb medicines, have drawn more and more attention in recent years. So far, 168 species of herbal plants belong to 58 genera, 24 families have been reported to contain xanthones. Among them, Calophyllum, Cratoxylum, Cudrania, Garcinia, Gentiana, Hypericum and Swertia genera are plant resources with great development prospect. This paper summarizes the plant resources, bioactivity and the structure-activity relationships (SARs) of xanthones from references published over the last few decades, which may be useful for new drug research and development on xanthones.

Cameroonian medicinal plants: a bioactivity versus ethnobotanical survey and chemotaxonomic classification

Background

In Cameroon herbs are traditionally used to meet health care needs and plans are on the way to integrate traditional medicine in the health care system, even though the plans have not been put into action yet. The country however has a rich biodiversity, with ~8,620 plant species, some of which are commonly used in the treatment of several microbial infections and a range of diseases (malaria, trypanosomiasis, leishmaniasis, diabetes and tuberculosis).

Methods

Our survey consisted in collecting published data from the literature sources, mainly from PhD theses in Cameroonian university libraries and also using the author queries in major natural product and medicinal chemistry journals. The collected data includes plant sources, uses of plant material in traditional medicine, plant families, region of collection of plant material, isolated metabolites and type (e.g. flavonoid, terpenoid, etc.), measured biological activities of isolated compounds, and any comments on significance of isolated metabolites on the chemotaxonomic classification of the plant species. This data was compiled on a excel sheet and analysed.

Results

In this study, a literature survey led to the collection of data on 2,700 secondary metabolites, which have been previously isolated or derived from Cameroonian medicinal plants. This represents distinct phytochemicals derived from 312 plant species belonging to 67 plant families. The plant species are investigated in terms of chemical composition with respect to the various plant families. A correlation between the known biological activities of isolated compounds and the ethnobotanical uses of the plants is also attempted. Insight into future direction for natural product search within the Cameroonian forest and Savanna is provided.

Conclusions

It can be verified that a phytochemical search of active secondary metabolites, which is inspired by knowledge from the ethnobotanical uses of medicinal plants could be very vital in a drug discovery program from plant-derived bioactive compounds.

Analgesic and anti-inflammatory effect of aqueous extract of the stem bark of Allanblackia gabonensis (Guttiferae)

Allanblackia gabonensis (Guttiferae) is a plant used in the African traditional medicine as remedies against pain, rheumatism, inflammations. In the present work, the analgesic effect of aqueous extract has been evaluated using acetic acid, formalin, hot-plate test, tail immersion and paw-pressure test. The anti-inflammatory effect of this extract was also investigated on carrageenan, histamine or serotonin induced by paw oedema. Aqueous extract of stem bark of A. gabonensis administrated p.o. showed significant activity against paw oedema induced by carrageenan, with a maximum percentage of inhibition reaching the 74.01% at the preventive test at a dose of 200 mg/kg. A. gabonensis exhibited a significant reduction of paw oedema induced by both histamine and serotonin with a maximal inhibition of 56.94% (200 mg/kg) and 40.83% (100 mg/kg), respectively. It showed significant protective effects against chemical stimuli (acetic acid and formalin) in the mouse. Administered orally at the doses of 100-400 mg/kg, exhibited protective effect of at least 69.78% on the pain induced by acetic acid and also reduced first (67.18% at 200 mg/kg) and second (83.87% at 400 mg/kg) phase of pain-induced par formalin. It also produced a significant increase of the threshold of sensitivity to pressure and hot plate-induced pain in the rats. These results suggest a peripheral and central analgesic activities as well as an anti-inflammatory effect of the stem bark of A. gabonensis.