David Guilet

Dihydrochalcones: implication in resistance to oxidative stress and bioactivities against advanced glycation end-products and vasoconstriction.

Flavonoids are a group of polyphenol compounds with known antioxidant activities. Among them, dihydrochalcones are mainly found in apple leaves (Malus domestica). Glycosylated dihydrochalcones were previously found in large amounts in leaves of two genotypes of Malus with contrasting resistance to fire blight, a bacterial disease caused by Erwinia amylovora. In the present study we demonstrate that soluble polyphenol patterns comprised phloridzin alone or in combination with two additional dihydrochalcones, identified as sieboldin and trilobatin. Presence of sieboldin in young leaves correlated well with a high 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging activity. Moreover, these leaves displayed enhanced tolerance to paraquat, a photooxidative-stress generating herbicide. Interestingly, phloridzin had a high activity in the oxygen radical absorbance capacity (ORAC) assay, but its presence alone in leaves did not correlate with tolerance to paraquat. In order to further characterise the activity of these compounds, we tested their ability to prevent oxidative-dependent formation of advanced glycation end-products (AGEs) and phenylephrine-induced contraction of isolated rat mesenteric arteries. The antioxidant capacity of sieboldin was clearly demonstrated by showing that this compound (i) prevented vasoconstriction and (ii) inhibited AGEs formation. Both assays provided interesting information concerning a potential use of sieboldin as a therapeutic. Hence, our results strongly argue for a bioactivity of dihydrochalcones as functional antioxidants in the resistance of Malus leaves to oxidative stress. In addition, we demonstrate for the first time that sieboldin is a powerful multipotent antioxidant, effective in preventing physiopathological processes. Further work should aim at demonstrating the potential use of this compound as a therapeutic in treating free radical-involving diseases.

Cytotoxic coumarins from Calophyllum dispar

Six coumarins have been isolated from the fruits and the stem bark of Calophyllum dispar (Clusiaceae). The structures of these minor components were established by means of spectroscopic analysis, including extensive 2D NMR studies. Some of these coumarins exhibited a significant cytotoxic activity against KB cells.

Cytotoxic and antiplasmodial xanthones from Pentadesma butyracea.

Four new xanthones, butyraxanthones A-D (1-4), were isolated from the stem bark of Pentadesma butyracea, together with six known xanthones (5-10) and a triterpenoid (lupeol). The structures of 1-4 were established by spectroscopic methods. Compounds 1-10 were tested in vitro for antiplasmodial activity against a Plasmodium falciparum chloroquine-resistant strain and for cytotoxicity against a human breast cancer cell line (MCF-7). Nearly all of these xanthones exhibited good antiplasmodial activity, and some of them also demonstrated potent cytotoxicity.

Bioguided fractionation and isolation of natural inhibitors of advanced glycation end-products (AGEs) from Calophyllum flavoramulum

Advanced glycation end-products (AGEs) are associated with many pathogenic disorders such as Alzheimers disease, pathogenesis of diabetes, atherosclerosis or endothelial dysfunction leading to cardiovascular events. Clusiaceae and Calophyllaceae families are rich in compounds like polyphenols which are able to inhibit their formation and are therefore of great interest. Calophyllum flavoramulum Hend. & Wyatt-Sm., a native Malaysian plant, was selected after an anti-AGEs screening conducted on DCM and MeOH extracts from plants belonging to these aforementioned families. In a first study, bioguided fractionation of the MeOH leaf extract of C. flavoramulum afforded amentoflavone, 3-methoxy-2-hydroxyxanthone, 3,4-dihydroxy-tetrahydrofuran-3-carboxylic acid, quercitrin, 3,4-dihydroxybenzoic acid, canophyllol and apetalactone. Amentoflavone and 3-methoxy-2-hydroxyxanthone were found to be very potent (IC(50)=0.05 and 0.06 mM respectively), while anti-AGEs activities of quercitrin and 3,4-dihydroxybenzoic acid appeared as moderately strong (IC(50)=0.5 mM). In a second study, a systematic phytochemical study of the cyclohexane, DCM and EtOAc extracts obtained from the same plant was conducted to isolate the following products: flavoramulone, 6-deoxyjacareubin, rheediachromenoxanthone, 2,3-dihydroamentoflavone and benzoic acid. 3,4-Dihydroxy-tetrahydrofuran-3-carboxylic acid and flavoramulone were isolated for the first time and their structures were identified by means of IR, MS and NMR spectrometries.

Breast cancer resistance protein (BCRP/ABCG2): new inhibitors and QSAR studies by a 3D linear solvation energy approach.

A series of compounds derived from naturally occurring flavonoids and synthetic analogs have been evaluated on cell lines overexpressing the wild-type breast cancer resistance protein (BCRP/ABCG2) half-transporter. Human ABCG2-transfected cells were used for screening their inhibitory activity. Five new natural compounds obtained from Morus mesozygia Stapf and one synthetic chromone, comprising a flavonoidic scaffold, were also evaluated. Based on the results obtained with a total of 34 compounds, a 3D linear solvation energy QSAR was investigated by VolSurf descriptors of molecular-interaction fields (MIFs) related to hydrophobic-interaction forces, polarisability and hydrogen-bonding capacity. Accuracy of the constructed 3D-QSAR model was attested by a correlation coefficient r(2) of 0.77. Shape parameters and hydrophobicity were revealed to be major physicochemical parameters responsible for the inhibition activity of flavonoid derivatives and synthetic analogs towards ABCG2, whereas hydrogen-bond donor capacity appeared highly unfavorable.

6-Acylcoumarins from Mesua racemosa

Abstract Two new 6-acylcoumarins, racemosol 1 and mammea A/AC cyclo F 2 were isolated by fractionation of a leave extract of Mesua racemosa (Planch. ex Triana and Planch.) Kostermans. Their structures were solved by extensive spectroscopic analysis as 5,7-dihydroxy-8- (2‴-hydroxy-3‴-methylbut-3‴-ene)-6- (1″-oxobutyl)-4-phenyl-2 H -benzo [ b ]pyran-2-one 1 and 5-hydroxy-8- (1‴-hydroxy-1‴-methylethyl)-6- (1″-oxobutyl)-4-phenyl-8,9-dihydro-2 H -furo [2′,3′:5,6]benzo [1,2-b]pyran-2-one 2. Five known compounds namely mammea A/AC 3, mammea A/AC cyclo D 4, mammea A/AD cyclo D 5, mammea A/BB 6 and mammea A/AA 7 were also isolated from the same source.

QTL analysis and candidate gene mapping for the polyphenol content in cider apple.

Polyphenols have favorable antioxidant potential on human health suggesting that their high content is responsible for the beneficial effects of apple consumption. They control the quality of ciders as they predominantly account for astringency, bitterness, color and aroma. In this study, we identified QTLs controlling phenolic compound concentrations and the average polymerization degree of flavanols in a cider apple progeny. Thirty-two compounds belonging to five groups of phenolic compounds were identified and quantified by reversed phase liquid chromatography on both fruit extract and juice, over three years. The average polymerization degree of flavanols was estimated in fruit by phloroglucinolysis coupled to HPLC. Parental maps were built using SSR and SNP markers and used for the QTL analysis. Sixty-nine and 72 QTLs were detected on 14 and 11 linkage groups of the female and male maps, respectively. A majority of the QTLs identified in this study are specific to this population, while others are consistent with previous studies. This study presents for the first time in apple, QTLs for the mean polymerization degree of procyanidins, for which the mechanisms involved remains unknown to this day. Identification of candidate genes underlying major QTLs was then performed in silico and permitted the identification of 18 enzymes of the polyphenol pathway and six transcription factors involved in the apple anthocyanin regulation. New markers were designed from sequences of the most interesting candidate genes in order to confirm their co-localization with underlying QTLs by genetic mapping. Finally, the potential use of these QTLs in breeding programs is discussed.

Regioselectivity in the ene reaction of singlet oxygen with ortho-prenylphenol derivatives

The ene reaction of singlet oxygen with prenylated dihydroxyacetophenones led to the 2-hydroperoxy-3-methylbut-3-enyl derivatives as the major product. This original regioselectivity outlined a new effect, in competition with the previously established large group non-bonding effect. The oxidation products distribution could be explained by a stabilising interaction between the phenolic hydrogen, ortho to the prenyl side chain, and the perepoxide intermediate.

Comparison of two methods, UHPLC-UV and UHPLC-MS/MS, for the quantification of polyphenols in cider apple juices.

The aim of this study was to develop faster and more efficient phenotyping methods for in-depth genetic studies on cider apple progeny. The UHPLC chromatographic system was chosen to separate polyphenolic compounds, and quantifications were then simultaneously performed with a UV-PDA detector and an ESI-triple quadrupole mass analyzer (SRM mode). Both quantification methods were validated for 15 major compounds using two apple juice samples, on the basis of linearity, limits of detection and quantification, recovery and precision tests. The comparison between UV and SRM quantifications in 120 different samples of a cider apple progeny showed an excellent correlation for major compounds quantified with both methods. However, an overestimation was revealed for five compounds with the UV detector and the mass analyzer. Co-elution and matrix effects are discussed to explain this phenomenon. SRM methods should therefore be considered with restrictions in some cases for quantification measurements when several phenolic compounds are simultaneously quantified in complex matrices such as apple juices. For both methods, analyses were carried out over short periods of time while maintaining a high quality for the simultaneous quantification of phenolic compounds in apple juice. Each method is relevant for more in-depth genetic studies of the polyphenol content of apple juice.

Antiangiogenic tocotrienol derivatives from Garcinia amplexicaulis.

Phytochemical investigation of a dichloromethane extract from Garcinia amplexicaulis stem bark led to the isolation of four new tocotrienols (1-4); two known tocotrienols, two triterpenes, and a xanthone were also isolated. Their structures were mainly established using NMR and MS methods. The main compounds isolated, δ-amplexichromanol (1) and γ-amplexichromanol (2), were evaluated on VEGF-induced angiogenesis using a Matrigel assay. Compounds 1 and 2 inhibited in vitro angiogenesis of VEGF-induced human primary endothelial cells in the low nanomolar range. Their capacity to inhibit VEGF-induced proliferation of endothelial cells partially explained this activity, although δ-amplexichromanol (1) also prevented adhesion and migration processes.