Origin of Dimethoxyserratene derivatives in a peat bog

Abstract : Due to the diversity of their skeleton, functional groups and configurations, pentacyclic triterpenes are molecular biomarkers that provide precious information on past local vegetation. When preserved in natural archives, and considering their taxonomical value, they can be used to track the evolution of past ecosystems through the time. For example, triterpenyl acetates are mainly produced by Asteraceae (Lavrieux et al., 2011) whereas pentacyclic triterpenes methyl ether are essentially biosynthesized by Poaceae (Jacob et al., 2005), both taxa representing open vegetation. Recently, various methoxyserratenes identified in coniferous forest soils (Le Milbeau et al., 2013) have been related to their source organisms, i.e. Pinaceae. Unravelling the past dynamics of this tree group is important because it is implicated in many Human activities (forestry). As part of our continuing effort to identify the source-product relationship between methoxyserratenes and Pinaceae, and to test whether these compounds can be preserved in various archives (soils, peats and sediments)we have analysed peat samples from La Guette peat bog (région Centre, France) with a focus on these compounds. Lipids were extracted by ASE, fractionated into polarity classes by liquid chromatography and analysed by gas chromatography coupled to mass spectrometry. A series of five methoxyserratenes were detected: 3β,21α-dimethoxyserrat-14-ene, 3α-methoxyserrat-14-en-21-one, 3β-methoxyserrat-14-en-21-one, 3-methoxyserrat-14-en-21α-yl acetate, 3-methoxyserrat-14-en-21β-ol. Additionally, three new serratene derivatives could be identified on the basis of their mass spectra. These serratenes, which have not previously been described in the literature, exhibit two methoxyl at C-3 and C-21 and a third oxygenated function (hydroxyl or acetoxyl) at C-29 position. Analysis reveals that stem bark of Pinus sylvestris are enriched in methoxyserratenes when compared to leaves. Both stems and leaves contain the five common methoxyserratenes that were detected in the peat samples but also the three new functionalized dimethoxyserratenes. This observation constitutes a strong argument for relating these three original methoxyserratenes to Pinus sylvestris. Our results thus confirm and extend the potential of methoxyserratenes as specific biomarkers of Pinaceae and provide for the first time evidence for their preservation in peat samples. REFERENCES Jacob J., Disnar J.R., Boussafir M., Sifeddine A., Albuquerque A.L.S., Turcq B., 2005. Pentacyclic triterpene methyl ethers in recent lacustrine sediments (Lagoa do Caçó, Brazil). Organic Geochemistry 36, 449–461. Lavrieux M., Jacob J., Le Milbeau C., Zocatelli R., Masuda K., Bréhéret, J.G., Disnar J.R., 2011. Occurrence of triterpenyl acetates in soil and their potential as chemotaxonomical markers of Asteraceae. Organic Geochemistry 42, 1315–1323. Le Milbeau C., Lavrieux, M., Jacob, J., Bréhéret, J.-G., Zocatelli, R., Disnar, J.-R., 2013. Methoxy-serratenes in a soil under conifers and their potential use as biomarkers of Pinaceae. Organic Geochemistry 55, 45-54.
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Poster communications
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Claude Le Milbeau, Jérémy Jacob, Renata Zocatelli, Sébastien Gogo, Fatima Laggoun-Défarge. Origin of Dimethoxyserratene derivatives in a peat bog . 26th International Meeting on Organic Geochemistry (IMOG 2013), Sep 2013, Tenerife, Spain. ⟨insu-01295797⟩

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