OMICS Approaches to Assess Dinoflagellate Responses to Chemical Stressors.

Dinoflagellates are important primary producers known to form Harmful Algae Blooms (HABs). In water, nutrient availability, pH, salinity and anthropogenic contamination constitute chemical stressors for them. The emergence of OMICs approaches propelled our understanding of dinoflagellates' responses to stressors. However, in dinoflagellates, these approaches are still biased, as transcriptomic approaches are largely conducted compared to proteomic and metabolomic approaches. Furthermore, integrated OMICs approaches are just emerging. Here, we report recent contributions of the different OMICs approaches to the investigation of dinoflagellates' responses to chemical stressors and discuss the current challenges we need to face to push studies further despite the lack of genomic resources available for dinoflagellates.

Synthesis and Investigation of Flavanone Derivatives as Potential New Anti-Inflammatory Agents.

Flavonoids are polyphenols with broad known pharmacological properties. A series of 2,3-dihydroflavanone derivatives were thus synthesized and investigated for their anti-inflammatory activities. The target flavanones were prepared through cyclization of 2'-hydroxychalcone derivatives, the later obtained by Claisen-Schmidt condensation. Since nitric oxide (NO) represents an important inflammatory mediator, the effects of various flavanones on the NO production in the LPS-induced RAW 264.7 macrophage were assessed in vitro using the Griess test. The most active compounds were flavanone (4G), 2'-carboxy-5,7-dimethoxy-flavanone (4F), 4'-bromo-5,7-dimethoxy-flavanone (4D), and 2'-carboxyflavanone (4J), with IC50 values of 0.603, 0.906, 1.030, and 1.830 µg/mL, respectively. In comparison, pinocembrin achieved an IC50 value of 203.60 µg/mL. Thus, the derivatives synthesized in this work had a higher NO inhibition capacity compared to pinocembrin, demonstrating the importance of pharmacomodulation to improve the biological potential of natural molecules. SARs suggested that the use of a carboxyl-group in the meta-position of the B-ring increases biological activity, whereas compounds carrying halogen substituents in the para-position were less active. The addition of methoxy-groups in the meta-position of the A-ring somewhat decreased the activity. This study successfully identified new bioactive flavanones as promising candidates for the development of new anti-inflammatory agents.

Biosorption of nickel ions Ni2+ by natural and modified Pinus caribaea Morelet sawdust.

The potential of Pinus caribaea Morelet sawdust for the removal of nickel ions (Ni2+) and other metallic trace ions (Co2+, Cr3+, Mn2+) from aqueous solutions was investigated under batch conditions. Several parameters such as size of particles, contact time, pH, initial metal and biomass concentrations, desorption conditions and reusability were evaluated on natural biomass. Biosorption was fast, effective (73%) and biomaterial can be reused after five cycles. To enhance the removal capacity of nickel, pine sawdust was modified by acidic and oxidative treatments. Cellulosic residues from sawdust sequential extraction showed great biosorption capacity (96%). In the presence of a metal mixture, oxidized sawdust had better selectivity for Cr3+ ions than for Ni2+ . Pinus caribaea biomass could be an environmental, inexpensive and renewable material for the depollution of water laden with metallic trace elements.

Antioxidant Compounds from Microalgae: A Review.

The demand for natural products isolated from microalgae has increased over the last decade and has drawn the attention from the food, cosmetic and nutraceutical industries. Among these natural products, the demand for natural antioxidants as an alternative to synthetic antioxidants has increased. In addition, microalgae combine several advantages for the development of biotechnological applications: high biodiversity, photosynthetic yield, growth, productivity and a metabolic plasticity that can be orientated using culture conditions. Regarding the wide diversity of antioxidant compounds and mode of action combined with the diversity of reactive oxygen species (ROS), this review covers a brief presentation of antioxidant molecules with their role and mode of action, to summarize and evaluate common and recent assays used to assess antioxidant activity of microalgae. The aim is to improve our ability to choose the right assay to assess microalgae antioxidant activity regarding the antioxidant molecules studied.

The effects of CO2-induced acidification on Tetraselmis biomass production, photophysiology and antioxidant activity: A comparison using batch and continuous culture.

A Tetraselmis sp. was selected for its antioxidant activity owing to its high lipid peroxidation inhibition capacity. With the aim to monitor culture conditions to improve antioxidant activity, effects of CO2-induced acidification on Tetraselmis growth, elemental composition, photosynthetic parameters and antioxidant activity were determined. Two pH values were tested (6.5 and 8.5) in batch and continuous cultures in photobioreactors. Acidification enhanced cell growth under both culture methods. However, the microalgae physiological state was healthier at pH 8.5 than at pH 6.5. Indeed, photosynthetic parameters measured with pulse amplitude modulated (PAM) fluorometry showed a decrease in the photosystem II (PSII) efficiency at pH 6.5 in batch culture. Yet, with the exception of the PSII recovering capacity, photosynthetic parameters were similar in continuous culture at both pH. These results suggest that lowering pH through CO2-induced acidification may induce a lower conversion of light to chemical energy especially when coupled with N-limitation and/or under un-balanced culture conditions. The highest antioxidant activity was measured in continuous culture at pH 6.5 with an IC50 of 3.44 ±â€¯0.6 µg mL-1, which is close to the IC50 of reference compounds (trolox and α-tocopherol). In addition, the principal component analysis revealed a strong link between the antioxidant activity and the culture method, the photophysiological state and the nitrogen cell quota and C:N ratio of Tetraselmis sp.. These results highlight Tetraselmis sp. as a species of interest for natural antioxidant production and the potential of PAM fluorometry to monitor culture for production of biomass with a high antioxidant activity.

Chemotaxonomy and cytotoxicity of the liverwort Porella Viridissima.

The first chemotaxonomic study based on volatile components of Porella viridissima (Mitt.) Grolle is reported. The GC-MS analysis of ether extract was performed; ten santalane and five pinguisane-type sesquiterpenes were identified together with perrottetianal A as major diterpene. Most of detected santalane-type sesquiterpenes are reported for the first time in liverwort. P. viridissima was found to belong to the chemotype III (pinguisane/sacculatane) and shared chemical similarities with P. navicularis. Perrotettianal A was isolated and has shown strong cytotoxicity against ovarian cancer.

Effects of Nitrogen Availability on the Antioxidant Activity and Carotenoid Content of the Microalgae Nephroselmis sp.

Nephroselmis sp. was previously identified as a species of interest for its antioxidant properties owing to its high carotenoid content. In addition, nitrogen availability can impact biomass and specific metabolites' production of microalgae. To optimize parameters of antioxidant production, Nephroselmis sp. was cultivated in batch and continuous culture conditions in stirred closed photobioreactors under different nitrogen conditions (N-repletion, N-limitation, and N-starvation). The aim was to determine the influence of nitrogen availability on the peroxyl radical scavenging activity (oxygen radical absorbance capacity (ORAC) assay) and carotenoid content of Nephroselmis sp. Pigment analysis revealed a specific and unusual photosynthetic system with siphonaxanthin-type light harvesting complexes found in primitive green algae, but also high lutein content and xanthophyll cycle pigments (i.e., violaxanthin, antheraxanthin, and zeaxanthin), as observed in most advanced chlorophytes. The results indicated that N-replete conditions enhance carotenoid biosynthesis, which would correspond to a higher antioxidant capacity measured in Nephroselmis sp. Indeed, peroxyl radical scavenging activity and total carotenoids were higher under N-replete conditions and decreased sharply under N-limitation or starvation conditions. Considering individual carotenoids, siphonaxanthin, neoxanthin, xanthophyll cycle pigments, and lycopene followed the same trend as total carotenoids, while ß-carotene and lutein stayed stable regardless of the nitrogen availability. Carotenoid productivities were also higher under N-replete treatment. The peroxyl radical scavenging activity measured with ORAC assay (63.6 to 154.9 µmol TE g-1 DW) and the lutein content (5.22 to 7.97 mg g-1 DW) were within the upper ranges of values reported previously for other microalgae. Furthermore, contents of siphonaxanthin ere 6 to 20% higher than in previous identified sources (siphonous green algae). These results highlight the potential of Nephroselmis sp. as a source of natural antioxidant and as a pigment of interest.

Synthesis, Optimization, Antifungal Activity, Selectivity, and CYP51 Binding of New 2-Aryl-3-azolyl-1-indolyl-propan-2-ols.

A series of 2-aryl-3-azolyl-1-indolyl-propan-2-ols was designed as new analogs of fluconazole (FLC) by replacing one of its two triazole moieties by an indole scaffold. Two different chemical approaches were then developed. The first one, in seven steps, involved the synthesis of the key intermediate 1-(1H-benzotriazol-1-yl)methyl-1H-indole and the final opening of oxiranes by imidazole or 1H-1,2,4-triazole. The second route allowed access to the target compounds in only three steps, this time with the ring opening by indole and analogs. Twenty azole derivatives were tested against Candida albicans and other Candida species. The enantiomers of the best anti-Candida compound, 2-(2,4-dichlorophenyl)-3-(1H-indol-1-yl)-1-(1H-1,2,4-triazol-1-yl)-propan-2-ol (8g), were analyzed by X-ray diffraction to determine their absolute configuration. The (-)-8g enantiomer (Minimum inhibitory concentration (MIC) = IC80 = 0.000256 µg/mL on C. albicans CA98001) was found with the S-absolute configuration. In contrast the (+)-8g enantiomer was found with the R-absolute configuration (MIC = 0.023 µg/mL on C. albicans CA98001). By comparison, the MIC value for FLC was determined as 0.020 µg/mL for the same clinical isolate. Additionally, molecular docking calculations and molecular dynamics simulations were carried out using a crystal structure of Candida albicans lanosterol 14α-demethylase (CaCYP51). The (-)-(S)-8g enantiomer aligned with the positioning of posaconazole within both the heme and access channel binding sites, which was consistent with its biological results. All target compounds have been also studied against human fetal lung fibroblast (MRC-5) cells. Finally, the selectivity of four compounds on a panel of human P450-dependent enzymes (CYP19, CYP17, CYP26A1, CYP11B1, and CYP11B2) was investigated.

Impact of Light Intensity on Antioxidant Activity of Tropical Microalgae.

Twelve microalgae species isolated in tropical lagoons of New Caledonia were screened as a new source of antioxidants. Microalgae were cultivated at two light intensities to investigate their influence on antioxidant capacity. To assess antioxidant property of microalgae extracts, four assays with different modes of action were used: 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2'-azino-bis (3-éthylbenzothiazoline-6-sulphonique) (ABTS), oxygen radical absorbance capacity (ORAC), and thiobabituric acid reactive substances (TBARS). This screening was coupled to pigment analysis to link antioxidant activity and carotenoid content. The results showed that none of the microalgae studied can scavenge DPPH and ABTS radicals, but Chaetoceros sp., Nephroselmis sp., and Nitzschia A sp. have the capacity to scavenge peroxyl radical (ORAC) and Tetraselmis sp., Nitzschia A sp., and Nephroselmis sp. can inhibit lipid peroxidation (TBARS). Carotenoid composition is typical of the studied microalgae and highlight the siphonaxanthin, detected in Nephroselmis sp., as a pigment of interest. It was found that xanthophylls were the major contributors to the peroxyl radical scavenging capacity measured with ORAC assay, but there was no link between carotenoids and inhibition of lipid peroxidation measured with TBARS assay. In addition, the results showed that light intensity has a strong influence on antioxidant capacity of microalgae: Overall, antioxidant activities measured with ORAC assay are better in high light intensity whereas antioxidant activities measured with TBARS assay are better in low light intensity. It suggests that different antioxidant compounds production is related to light intensity.

Biological exploration of a novel 1,2,4-triazole-indole hybrid molecule as antifungal agent.

(2-(2,4-Dichlorophenyl)-3-(1H-indol-1-yl)-1-(1,2,4-1H-triazol-1-yl)propan-2-ol (8 g), a new 1,2,4-triazole-indole hybrid molecule, showed a broad-spectrum activity against Candida, particularly against low fluconazole-susceptible species. Its activity was higher than fluconazole and similar to voriconazole on C. glabrata (MIC90 = 0.25, 64 and 1 µg/mL, respectively), C. krusei (MIC90 = 0.125, 64 and 0.125 µg/mL, respectively) and C. albicans (MIC90 = 0.5, 8 and 0.25 µg/mL, respectively). The action mechanisms of 8 g were also identified as inhibition of ergosterol biosynthesis and phospholipase A2-like activity. At concentration as low as 4 ng/mL, 8g inhibited ergosterol production by 82% and induced production of 14a-methyl sterols, that is comparable to the results obtained with fluconazole at higher concentration. 8 g demonstrated moderate inhibitory effect on phospholipase A2-like activity being a putative virulence factor. Due to a low MRC5 cytotoxicity, this compound presents a high therapeutic index. These results pointed out that 8 g is a new lead antifungal candidate with potent ergosterol biosynthesis inhibition.

Chemodiversity of Calophyllum inophyllum L. oil bioactive components related to their specific geographical distribution in the South Pacific region.

BACKGROUND: Different parts of the tree Calophyllum inophyllum L. (nuts, leaves, roots, bark, fruits, nut oil and resin) are used as traditional medicines and cosmetics in most of the Pacific Islands. The oil efficiency as a natural cure and in traditional cosmetics has been largely described throughout the South Pacific, which led us to investigate C. inophyllum's chemical and genetic diversity. A correlative study of the nut resin and leaf DNA from three distinct archipelagos in the South Pacific was carried out in order to identify diversity patterns in C. inophyllum across the South Pacific. METHODS: Calophyllum inophyllum plants were sampled from French Polynesia, New Caledonia and Fiji. We extracted tamanu oil (nut oil) resin for chemo-diversity studies and sampled leaf tissues for genetic studies. We applied an analysis method designed for small quantities (at a microscale level), and used High Performance Liquid Chromatography (HPLC) to establish the chemo-diversity of tamanu oil resin. In-house standards were co-eluted for qualitative determination. Genetic diversity was assessed using chloroplast barcoding markers (the Acetyl-CoA carboxylase (accD) gene and the psaA-ycf3 intergenic spacer region). RESULTS: Our HPLC analysis revealed 11 previously known tamanu oil constituents, with variability among plant samples. We also isolated and characterized two new neoflavonoids from tamanu oil resin namely, tamanolide E1 and E2 which are diastereoisomers. Although genetic analysis revealed low genetic variation, our multivariate analysis (PCA) of the tamanu oil resin chemical profiles revealed differentiation among geographic regions. CONCLUSION: We showed here that chromatographic analysis using formalized in-house standards of oil resin compounds for co-elution studies against oil resin samples could identify patterns of variation among samples of C. inophyllum, and discriminate samples from different geographical origins.

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.

Mechanisms of action and structure-activity relationships of cytotoxic flavokawain derivatives.

22 Flavokawain derivatives (FKd) were obtained by one step syntheses in order to conduct a SAR study to understand the structural requirements for optimum and selective cytotoxicity. FKd and natural flavokawains A and B found into kava, a South Pacific traditional beverage, were evaluated against nine cancer and one healthy cell lines. The targeted cell cycle phases as well as the effects on the induction of apoptosis and cell cycle protein levels were investigated. Therapeutic improvements (more activity and selectivity) were achieved with FKd compared to natural flavokawains and notably with the 2',3,4',6'-tetramethoxychalcone (FKd 19). FKd induced a G1/S arrest on p53 wild-type cells and an M arrest on p53 mutant-type, via the up-regulation of p21 and cyclin B1 proteins, followed by apoptosis. Moreover, FKd exhibited a 24h-effect on Akt/mTor normal cells versus a 48h-effect on Akt/mTor up-regulated cells. The SAR study resulted in the conclusion that trimethoxy A-ring allowed the best compromise between cytotoxicity and selectivity, as well as the substitution of the meta position on the B-ring and the use of halogens substituents.

Chemical Composition and Acaricidal Activity of Nemuaron vieillardii Essential Oil against the Cattle Tick Rhipicephalus (Boophilus) microplus.

Essential oil from leaves of Neinuaron vieilardii (Baill.) Baill., a shrub used in the kanak pharmacopeia, was analyzed by gas chromatography and combined. gas chromatography-mass spectrometry. The main compounds identified were safrole (49.7%), linalool (8.0%), 5-cadinene (5.1%), caryophyllene oxide.(4%) and A-6opaene (2.4%). This chemical composition is consistent with leaf oils of the Atherospermataceae family and demonstrates the proximity of the two genera Nemnuaron and Atherosperma as regards to their essential oil compositions. The modified Larval Packet Test (LPT) was used to assess acaricidal effect of N. viefflardii essential oil on larvae of the cattle tick Rhipicephalus (Boophilus) microplus and LC(50) was then calculated to 14.67%. High content of safrole in this oil which is suspected of being a human carcinogen, poses the problem of the use of this oil in a perspective of development of alternative tick control strategy and in the traditional medicinal consumption of Nemuaron vieillardii.

Volatile Constituents of New Caledonian Frullania Species.

Volatile components of seven Frullania species (Frullaniaceae) from New Caledonia, including five endemic species (F. bella, F. scalaris, F. mamnmillosa, F. cornita and F. falsicornuta), were analyzed by GC-MS in order to index these plants to known chemotypes. Constituents detected in these Frullania species were mainly sesquiterpenes, as well as the bibenzyl dihydrognetin, and the flavonoid naringinin-5,7,4'-trimethyl ether. These compositions allowed an indexation of Frullania species from New Caledonia to cyclocolorenone, sesquiterpene lactone and bibenzyl chemotypes. In addition, qualitative intraspecies variations of chemical composition were very important and made indexation to known chemotypes very tricky. Moreover, two of the endemic liverworts did not possess any biomarker that linked to a known chemotype.

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.

The Wound Healing and Antibacterial Activity of Five Ethnomedical Calophyllum inophyllum Oils: An Alternative Therapeutic Strategy to Treat Infected Wounds.

BACKGROUND: Calophyllum inophyllum L. (Calophyllaceae) is an evergreen tree ethno-medically used along the seashores and islands of the Indian and Pacific Oceans, especially in Polynesia. Oil extracted from the seeds is traditionally used topically to treat a wide range of skin injuries from burn, scar and infected wounds to skin diseases such as dermatosis, urticaria and eczema. However, very few scientific studies reported and quantified the therapeutic properties of Calophyllum inophyllum oil (CIO). In this work, five CIO from Indonesia (CIO1), Tahiti (CIO2, 3), Fiji islands (CIO4) and New Caledonia (CIO5) were studied and their cytotoxic, wound healing, and antibacterial properties were presented in order to provide a scientific support to their traditional use and verify their safety. METHODS: The safety of the five CIO was ascertained using the Alamar blue assay on human keratinocyte cells. CIO wound healing properties were determined using the scratch test assay on human keratinocyte cells. CIO-stimulated antibacterial innate immune response was evaluated using ELISA by measuring ß defensin-2 release in human derivative macrophage cells. CIO antibacterial activity was tested using oilogramme against twenty aerobic Gram- bacteria species, twenty aerobic Gram+ bacteria species, including a multi-drug resistant Staphylococcus aureus strain and two anaerobic Gram+ bacteria species e.g. Propionibacterium acnes and Propionibacterium granulosum. To detect polarity profile of the components responsible of the antibacterial activity, we performed bioautography against a Staphylococcus aureus strain. RESULTS: Based on Alamar Blue assay, we showed that CIO can be safely used on keratinocyte cells between 2.7% and 11.2% depending on CIO origin. Concerning the healing activity, all the CIO tested accelerated in vitro wound closure, the healing factor being 1.3 to 2.1 higher compared to control when keratinocytes were incubated after scratch with CIO at 0.1%. Furthermore, our results showed that CIO exhibit two distinct antibacterial effects: one against Gram+ bacteria by direct inhibition of mitotic growth and another potent effect against Gram- bacteria due to increased release of ß-defensin 2 peptide by macrophages. Interestingly, the needed concentrations of CIO to inhibit bacteria growth and to promote wound healing are lower than concentrations exhibiting cytotoxic effects on keratinocyte cells. Finally, we performed bioautography assay against Staphylococcus aureus to determine polarity profile of the components responsible for CIO antibacterial activity. Our results showed for the five tested CIO that components responsible of the bacterial growth inhibition are the more polar one on the TLC chromatographic profile and are contained in the resinous fraction of the oil. CONCLUSIONS: This study was conducted to evaluate cytotoxicity, wound healing and antibacterial properties of five CIO traditionally used to treat infected wounds. Using cell and bacteria cultures, we confirmed the pharmacological effects of CIO as wound healing and antimicrobial agent. Moreover, we showed that concentration of CIO needed to exhibit therapeutic effects are lower than concentrations exhibiting cytotoxic effects in vitro. For the first time, this study provides support for traditional uses of CIO. These wound healing and antibiotic properties make CIO a valuable candidate to treat infected wounds especially in tropical areas.

The leaf, wood and bark oils of three species of Myodocarpus (Myodocarpaceae) endemic to New Caledonia.

The leaf, wood and bark oils of three species of Myodocarpus, M. viellardii Brongn. & Gris, M. fraxinifolius Brongn. & Gris and M. lanceolatus Dubard & R. Viguier have been examined. From the wood oil of M. viellardii the major components were α-pinene (22.4%) and a monoterpene methyl ester, methyl myodocarpate (methyl 3,7-dimethylbicyclo [4,1,0]hept-3-ene-7-carboxylate) (61%), based on the δ-3-carene skeleton. Also present in lesser amounts was the corresponding acid, myodocarpic acid (3,7-dimethylbicyclo[4,1,0]hept-3-ene-7-carboxilic acid) and the corresponding alcohol, myodocarpol (3,7- dimethylbicyclo[4,1,0]hept-3-en-7-yl) methanol), in lesser (< 3%) amounts. The bark oil contained ß-caryophyllene (13.8%) and a series of long chain fatty alcohols, dodecanol, tetradecanol, hexadecanol, octadecanol and octadec-9-en-1-ol in amounts of 1.4-15% (all but octadecanol > 11%). The leaf oil of this species produced a sesquiterpenic oil with the principal components being ß-caryophyllene (36%), α-humulene (11.1%) and bicyclogermacrene (10.6%). In M. fraxinifolius, both the wood and bark oils contained a series of long chain alcohols, tetradecanol (30-38%), hexadecanol (23-29%) and octadec-9-en-1-ol (12%) as principal components. In the leaf oil of this species the principal component was ß-caryophyllene (63%), with lesser amounts of humulene oxide II (2.9%), isocomene (2.8%) and viridiflorol (1.4%). In M. lanceolatus, the leaf oil was dominated by the monoterpene hydrocarbons α-pinene (22.9%) and δ-3-carene (32.6%). In the wood oil of this species the principal components were geraniol (7.4%), citronellol (4.7%), germacrene-B (7.1%), zingiberine (6.8%) and linalool (6.7%), while in the bark oil they were geraniol (12.4%), citronellol (2.6%), germacrene-B (5.8%), and linalool (6.5%).

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

Dengue virus is the world's 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.