Sylvain Sutour

Composition and chemical variability of Mentha suaveolens ssp. suaveolens and M. suaveolens ssp. insularis from Corsica.

A detailed analysis of two essential oils from individual plants of Mentha suaveolens ssp. suaveolens growing wild in Corsica was carried out by combination of GC(RI), GC/MS, and 13C‐NMR analyses. One oil sample is characterized by the pre‐eminence of piperitenone oxide, and the second is dominated by piperitenone. In contrast, it was reported that the essential oil of M. suaveolens ssp. insularis, an endemic species to Corsica and Sardinia, contained pulegone and cis‐cis‐p‐menthenolide as main components. A principal‐component analysis (PCA) carried out on the composition of the essential oil of 59 individual plants of M. suaveolens sp. allowed the classification into three well‐defined groups. All the oil samples from Mentha suaveolens ssp. insularis belonged to the same group, while the oils from M. suaveolens ssp. suaveolens were distributed in the two other groups. The composition of the essential oil isolated from aerial parts of M. suaveolens ssp. has been shown to be an additional tool to differentiate the botanically close subspecies suaveolens and insularis.

Chemical Composition of Laurencia obtusa Extract and Isolation of a New C15-Acetogenin

A new C15-acetogenin, sagonenyne (20), exhibiting an unusual single tetrahydropyran ring was isolated from an ethyl acetate extract of Laurencia obtusa collected on the Corsican coastline. Its structure was established by detailed NMR spectroscopic analysis, mass spectrometry, and comparison with literature data. Twenty-three known compounds were identified in the same extract by means of column chromatography steps, using a 13C-NMR computer aided method developed in our laboratory. In addition to sesquiterpenes, which represent the main chemical class of this extract, diterpenes, sterols, and C15-acetogenins were identified. The crude extract was submitted to a cytotoxicity assay and was particularly active against THP-1 cells, a human leukemia monocytic cell line.

Halogenated C15 Acetogenin Analogues of Obtusallene III from a Laurenciella sp. Collected in Corsica

NMR chemical profiling of a Laurenciella sp. using a computerized method developed in our laboratory resulted in the identification of five new compounds (1-5) and 17 known compounds, among which 3-(E)-laurenyne represented by far the most abundant metabolite. Compounds 1 to 5 were isolated and fully characterized by detailed spectroscopic analysis. The absolute configuration and structural features of compound 1 were determined by single-crystal X-ray diffraction analysis. Compounds 1 to 4 are 12-membered cyclic ether acetogenins that are present in solution as interconverting conformers exhibiting an (aR) configuration of the bromoallene unit together with an S configuration at C-4. Among these, compound 3 is the first obtusallene derivative with bromine substituents at both the C-7 and C-12 positions. Compound 5 is an acetogenin bearing a [5.5.1]bicyclotridecane ring system. A plausible biosynthetic route to 1-4 is proposed.

Chemical composition of leaf and bark essential oils of Vepris unifoliolata from Madagascar

Abstract The chemical composition of leaf essential oil of Vepris unifoliolata was characterized by hydrocarbon monoterpenes, α-pinene (60.5%), myrcene (6.8%), limonene (5.1%), (E)-β-ocimene (4.9%) and β-phellandrene (4.7%). The chemical composition of bark essential oil of V. unifoliolata was original and characterized by a high content in heat-sensitive compounds isofuranodiene (43.9%) and germacrone (17.1%). These compounds bearing the (E,E)-1,5-cyclodecadiene structure were known to rearrange and degrade during the GC–FID and GC-MS. The true content of isofuranodiene/curzerene, germacrone/trans-β-elemenone, germacrene A/β-elemene and germacrene B/γ-elemene was evaluated by combination of 13C-NMR data (intensities of signals of selected carbons) and GC–FID. Thus, a correct quantitative analysis of bark oil of V. unifoliolata was provided.

Discrimination and Characterization of Two Mediterranean Species from the Laurencia Complex (Rhodomelacea) Using an NMR‐Based Metabolomic Approach

Generic and specific determination among the Laurencia complex is a challenging task. DNA barcoding combined with phenotypic investigations are mandatory for species differentiation. In this study, two morphologically different members of the Laurencia complex were investigated using untargeted 1H‐NMR‐based metabolomics. Twenty‐one population samples were collected in order to evaluate both temporal and geographical homogeneity. Data obtained from 1H‐NMR analysis followed by statistical analysis allowed a clear separation of all the samples into two groups. DNA mitochondrial tests confirmed this pattern and identified the two species as Laurenciella sp. and Laurencia obtusa. In addition, metabolites responsible of this discrimination were investigated directly in crude extracts by 13C‐NMR using an in‐house computer‐assisted method. The combination of both untargeted (1H) and targeted (13C) NMR‐based metabolomic approaches proves to be a powerful and complementary approach to discriminate species from the Laurencia complex.

New Metabolites Isolated from a Laurencia obtusa Population Collected in Corsica

The chemical investigation of an ethyl acetate extract (EtOAc) obtained from Laurencia obtusa, collected in Corsica, allowed for the identification of three new compounds (1, 2, and 4) and six known compounds. Compounds 1 to 4 were isolated and fully characterized by a detailed spectroscopic analysis. Compounds 1 and 2 are two C15-acetogenins sharing the same ring system: a tetrahydropyran linked by a methylene to a tetrahydrofuran ring. Compound 1 exhibits a bromoallene unit whereas compound 2 possesses an uncommon α-bromo-α,β-unsaturated aldehyde terminal unit. Compound 4 is the first diterpene exhibiting a 19(4→3)abeo-labdane skeleton isolated from a Laurencia species. Isolation of concinndiol (compound 3) together with compound 4 suggests a common biosynthetic origin. Additionally, five known compounds, namely sagonenyne, laurene, α-bromocuparene, microcladallene A, and β-snyderol were identified in chromatographic fractions by NMR analysis using a computerized method that was developed in our laboratory.

Anti-Quorum Sensing Activity of 12 Essential Oils on chromobacterium violaceum and Specific Action of cis-cis-p-Menthenolide from Corsican Mentha suaveolens ssp. Insularis

Quorum sensing (QS) is a bacterial communication mechanism used to express various survival or virulence traits leading to enhanced resistance. Chromobacterium violaceum is a commonly used strain that highlights anti-QS action of bioactive substances. Here, we wanted to see if 12 selected essential oils (EO) could exert anti-QS activity. We measured the sublethal minimal QS inhibitory concentration (MQSIC) by assessing violacein production of C. violaceum along with bacterial growth. To confirm the QS disruption, we also proceed to surface bacterial observations using scanning electron microscopy (SEM). We showed that cis-cis-p-menthenolide extracted and isolated from a plant endemic to occidental Mediterranean Sea islands, Mentha suaveolens ssp. insularis, acts as an inhibitor of violacein production and biofilm formation. Measured MQSIC was much lower than the minimal inhibitory concentration (MIC): 0.10 mg·mL−1 vs. 3.00 mg·mL−1. Moreover, disturbance of QS-related traits was confirmed by the degradation of C. violaceum biofilm matrix. There is a clear structure–activity relationship between cis-cis-p-menthenolide and anti-QS activity. Indeed, its isomer molecule (mintlactone) exerts a poor anti-QS action. These results indicate that inhibition of violacein production and biofilm formation by cis-cis-p-menthenolide might be related to a disruption in the QS mechanism.