Abstract: If plants are known for centuries as a valuable source of molecules, complexity remains and can open up numerous perspectives. Plants have indeed evolved a wide range of secondary metabolites as defense, competition or attraction compounds [1]. More particularly, the exceptional biodiversity encountered in the tropics, along with the presence of various pathogens and a strong herbivory especially linked to a rich entomofauna, leads to a promising chemodiversity, due to the constant and dynamic interactions between plants and their environment. Taking into account the role and “raison d'être”[2] of natural products, and the fact that all these molecules work together as complex mixtures can therefore lead to a new point of view, by shifting from the “magic bullet” classical approach to a “herbal shotgun” strategy[3]. We will illustrate the fact that, inspired by their ecological functions, and taking into account synergistic interactions, some therapeutic applications can be found for these versatile mixtures of compounds. In particular we examined whether the antidermatophytic activity of essential oils (EOs) obtained from particularly fragrant plant species from French Guiana could be used as an indicator for the discovery of active natural products against Leishmania amazonensis. A significant correlation was observed between antidermatophytic and antileishmanial activity, confirming the “alternative use” strategy in the case of EOs, and allowed us to highlight P. hispidum Sw. (Piperaceae) EO as a promising antileishmanial product [4]. We also illustrated the importance of synergistic effects through the example of the antifungal EO of Otacanthus azureus (Linden) Ronse (Plantaginaceae) [5] and the biomimetic design of optimized synergistic mixtures thanks to a full factorial experiment approach.

Abstract: Psidium acutangulum Mart. ex DC is used exclusively by the Wayana Amerindians in French Guiana, more particularly for the treatment of malaria. To understand this specific use, we embarked upon evaluating the antimalarial and anti-inflammatory activities of this traditional remedy as prepared by the Amerindian users. The decoction exerted good antiplasmodial activity in vitro (IC50 4 µg/ml on P. falciparum FcB1) and in vivo (39.7% inhibition of P. berghei NK65 in the murine model at 2 × 150 µl/day), as well as a strong anti-inflammatory effect in vitro regarding IL-1β, IL-6 and IL-8. Fractionation of the ethyl acetate extract (IC50 < 1 µg/ml) led to the isolation of six pure compounds, two of them, guaijaverine and the new compound wayanine, being moderately active against P. falciparum FcB1 in vitro (IC50 5 – 7 µg/ml). Along with the absence of cytotoxicity of the decoction and pure compounds, these results support the traditional use of this plant.

Abstract: Control of metal corrosion is of technical, economical, environmental, and aesthetical importance. The use of corrosion inhibitors is one of the best options to protect metals and alloys from corrosion. The environmental toxicity of synthetic inhibitors has prompted the search for green compounds. Plant extracts have become important as an environmentally acceptable, readily available and renewable source for a wide range of biodegradable, heavy metals-free inhibitors. Among natural compounds, alkaloids have very high corrosion inhibition efficiency. An alkaloidic extract of Geissospermum laeve (Apocynaceae) has been fractionated by centrifugal partition chromatography using the pH-zone refining mode in order to investigate the effect of isolated alkaloids on C38 steel corrosion in HCl 1M. Indole alkaloids were identified by LC-MS, 1H and 13C NMR.

Abstract: We determined the chemical composition and investigated the antifungal activity of Otacanthus azureus (Linden) Ronse essential oil alone or combined with azoles antifungals against a range of human yeasts and dermatophytes. The oil was shown to be composed in majority of sesquiterpenes. Using broth microdilution techniques, it was found to exert interesting in vitro antifungal activities, more particularly against human dermatophytes, with minimum inhibitory concentrations as low as 4µg/ml against a clinical isolate of Trichophyton rubrum. The analysis of the combined effect of this oil with azoles highlighted a pronounced synergism between the oil and ketoconazole or itraconazole, against Candida albicans, C. parapsilosis and Trichophyton mentagrophytes, with fractional inhibitory concentration indices in the 0.1–0.5 range. Interestingly, the oil showed no cytotoxicity on VERO cells (ED50>100µg/ml). According to these results, O. azureus essential oil may be considered a promising natural product in the treatment of human mycoses, more particularly those originating from dermatophytic fungi. Also, it is likely to reduce the minimum effective dose of ketoconazole and itraconazole against Candida species, thus minimizing the side effects of these drugs, and the risk to develop resistances.

Abstract: There is a general agreement that natural volatile compounds of essentials oils from plants provide a great potential for discovery of new antimicrobial drugs such as anticandidal ones. In this work, 60 commercial essential oils were analysed by GC/MS and their inhibitory activity against the growth of three Candida strains was evaluated. We then conducted a chemometric analysis and proposed a tool to predict their capacity to inhibit the Candida sp. developpment. Raw data were pretreated and normalised using MZmine2.2 software. It was possible to identify some of the natural compounds with anticandidal properties using two statistical tools in XLstat7.5: hierarchical clustering analysis (HAC) and principal component analysis (PCA). We highlighted that essential oils containing limonene, 1,8-cineole, linalool and linalyl acetate were mostly inactive, whereas eugenol, thymol, carvacrol, geraniol, geranial and neral as major components of the oils seems to be linked to an interesting anticandidal activity. Linear regressions showed a high correlation between the concentration of these molecules and their antifungal activity. Exceptions to these general tendencies could be characteristic of synergistic or antagonistic interactions.