Edouard Hnawia

Vedelianin, a hexahydroxanthene derivative isolated from Macaranga vedeliana☆

Abstract A methanolic extract of the leaves of Macaranga vedeliana furnished a new hexahydroxanthene derivative, vedelianin, which can be considered as a substituted cyclized geranylstilbene.

A geranyl substituted flavonol from Macaranga vedeliana

Abstract The methanolic extract of the leaves of Macaranga vedeliana furnished a new flavonol, macarangin (6-[( E )-3″,8″-dimethyl-2″,7″-octadienyl]kaempferol).

Structure-activity relationship study of biflavonoids on the Dengue virus polymerase DENV-NS5 RdRp.

Dengue virus is the worlds most prevalent human pathogenic arbovirus. There is currently no treatment or vaccine, and solutions are urgently needed. We previously demonstrated that biflavonoids from Dacrydium balansae, an endemic gymnosperm from New Caledonia, are potent inhibitors of the Dengue virus NS5 RNA-dependent RNA polymerase. Herein we describe the structure-activity relationship study of 23 compounds: biflavonoids from D. balansae (1-4) and from D. araucarioides (5-10), hexamethyl-amentoflavone (11), cupressuflavone (12), and apigenin derivatives (13-23). We conclude that 1) over the four different biflavonoid skeletons tested, amentoflavone (1) and robustaflavone (5) are the most promising ones for antidengue drug development, 2) the number and position of methyl groups on the biflavonoid moiety modulate their inhibition of Dengue virus NS5 RNA-dependent RNA polymerase, and 3) the degree of oxygenation of flavonoid monomers influences their antidengue potential. Sotetsuflavone (8), with an IC50 = 0.16 µM, is the most active compound of this series and is the strongest inhibitor of the Dengue virus NS5 RNA-dependent RNA polymerase described in the literature.

Antiplasmodial activity of New Caledonia and Vanuatu traditional medicines

Context: With the emergence of strains multiresistant to antimalarial drugs, the search for new active molecules remains a priority. Ethnopharmacology appears to be a good method of selection in such investigations. Objective: The aim of this research work is to select plants used in Melanesian traditional medicine, in New Caledonia and Vanuatu, which should be a promising source for the isolation of new antimalarial drugs. Materials and methods: Forty-seven plant extracts belonging to 12 families, traditionally used by the Melanesian people or belonging to an antimalarial known genus, were screened in vitro for antimalarial activity on Plasmodium falciparum chloroquine (CQ)-resistant (FcB1) and CQ-sensitive (HB3) strains. They were also tested for their inhibitory effects on a protein kinase (Pfnek) and their cytotoxicity on human breast adenocarcinoma (MCF7) cells. Results: Among all extracts, four displayed strong in vitro activities against P. falciparum: Gardenia urvillei Montrouzier, Scleria polycarpa Boeckeler, Terminalia catappa L. and Acronychia laevis J.R. & J.G. Forster, the latter being also toxic on MCF7 cells. Except for the extracts of S. polycarpa, all others that were active on P. falciparum, also possess an inhibitory effect on Pfnek. Discussion and conclusion: These results confirm that ethnopharmacology is an excellent approach for such investigations. The two countries considered clearly present advantages in the field. Indeed, local populations keep their traditional knowledge alive, and their flora is exceptionally rich. In New Caledonia, the high endemicity rate (74%) ranks the island as one of the world’s biodiversity hotspots. As a consequence, chances to discover new active natural compounds are also high.

An examination of the leaf essential oils of the endemic Melaleuca (Myrtaceae) species of New Caledonia

The leaf essential oils of the seven endemic New Caledonian species of the genus Melaleuca have been examined. Melaleuca sphaerodendra var. microphylla and Melaleuca brevisepala produced oils in which β-caryophyllene (28.8% and 26.8% respectively) was the principal component. α-Pinene (24.8%) and β-caryophyllene (14.1%) were the principal compounds detected in the leaf oil of Melaleuca pancheri. Melaleuca brongniartii produced an oil in which the principal monoterpenes were α-pinene (23.3%), β-pinene (10.3%) and limonene (19.8%). γ-Terpinene (15.2%), p-cymene (12.8%) and terpinolene (17.5%) were the major components in the leaf essential oil of Melaleuca buseana, whereas the leaf oil of Melaleuca dawsonii contained α-pinene (12.8%) and α-phellandrene (10.3%) as principal components. In Melaleuca gnidioides α-pinene (23.6%), β-pinene (13.6%) and spathulenol (14.7%) were the major components. All of these oils differed from the leaf oil of Melaleuca quinquenervia, an indigenous New Caledonian species also found in Australia and New Guinea.

Chemical Diversity of Podocarpaceae in New Caledonia: Essential Oils from Leaves of Dacrydium, Falcatifolium, and Acmopyle Species.

Plant secondary metabolites can be useful chemosystematic markers to distinguish species at different taxonomy levels. For example, sesquiterpenes and diterpenes show specific distribution patterns within conifers and so provide especially precious information about the diversity and evolutionary relationships of this group. The aim of the present study was to provide a first insight into the terpene diversity of endemic Podocarpaceae from New Caledonia. The leaf essential oils of Dacrydium araucarioides Brongn. & Gris, Dacrydium balansae Brongn. & Gris, Dacrydium guillauminii J.Buchholz, Dacrydium lycopodioides Brongn. & Gris, Falcatifolium taxoides (Brongn. & Gris) de Laub., and Acmopyle pancheri (Brongn. & Gris) Pilg. from New Caledonia were characterized by GC/FID and GC/MS analyses, and the chemotaxonomic relationships of these species were determined by comparison of their terpene compositions. Cluster analysis based on the biosynthetic origin of their volatile terpenes led to the description of three distinct groups of essential oils and showed close relationships between those of D. araucarioides and D. balansae as well as between those of A. pancheri and F. taxoides.

Chemotypes and Biomarkers of Seven Species of New Caledonian Liverworts from the Bazzanioideae Subfamily

Volatile components of seven species of the Bazzanioideae sub-family (Lepidoziaceae) native to New Caledonia, including three endemic species (Bazzania marginata, Acromastigum caledonicum and A. tenax), were analyzed by GC-FID-MS in order to index these plants to known or new chemotypes. Detected volatile constituents in studied species were constituted mainly by sesquiterpene, as well as diterpene compounds. All so-established compositions cannot successfully index some of them to known chemotypes but afforded the discovery of new chemotypes such as cuparane/fusicoccane. The major component of B. francana was isolated and characterized as a new zierane-type sesquiterpene called ziera-12(13),10(14)-dien-5-ol (23). In addition, qualitative intraspecies variations of chemical composition were very important particularly for B. francana which possessed three clearly defined different compositions. We report here also the first phytochemical investigation of Acromastigum species. Moreover, crude diethyl ether extract of B. vitatta afforded a new bis(bibenzyl) called vittatin (51), for which a putative biosynthesis was suggested.