Characterization of bioactive plant ellagitannins by chromatographic, spectroscopic and mass spectrometric methods
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CHEMOECOLOGY
RESEARCH PAPER
Characterization of bioactive plant ellagitannins by chromatographic, spectroscopic and mass spectrometric methods Johanna Moilanen • Jari Sinkkonen Juha-Pekka Salminen
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Received: 5 December 2012 / Accepted: 2 April 2013 Ó Springer Basel 2013
Abstract Ellagitannins are widely distributed plant polyphenols showing potent anti-herbivore activities, but rather complex chemical structures. Here we show how ellagitannins with different structures can be efficiently characterized from plant extracts by utilizing the information obtained from four universal methods used for ellagitannin analysis: Sephadex LH-20 gel chromatography, high-performance liquid chromatography, ultraviolet spectroscopy, and mass spectrometry. We show that by combining the information obtained from the ellagitannins’ chromatographic elution order, specific shapes of the ultraviolet spectra, molecular masses and characteristic mass spectral fragmentations, it is possible to classify these polyphenols into different ellagitannin sub-groups, and even characterize the structures within the sub-groups. These findings aid in the fast screening of complex plant samples for their ellagitannin composition without having to isolate compounds for individual characterization. Keywords Polyphenol Hydrolyzable tannin Structure elucidation
Electronic supplementary material The online version of this article (doi:10.1007/s00049-013-0132-3) contains supplementary material, which is available to authorized users. J. Moilanen (&) J. Sinkkonen J.-P. Salminen Laboratory of Organic Chemistry and Chemical Biology, Department of Chemistry, University of Turku, 20014 Turku, Finland e-mail: [email protected]
Introduction Ellagitannins (ETs) are a sub-class of hydrolyzable tannins, which are found in numerous plant families of the dicotyledonous plants of Angiospermae. The structural diversity of ETs is substantial, and nowadays over 500 ETs have been characterized and identified (Okuda et al. 2009). Despite the number of different compounds, they are all derived from pentagalloyl glucose (PGG, Fig. 1a) by oxidative coupling of two (or more) neighboring galloyl groups (Niemetz and Gross 2005; Gross 2009). The hexahydroxydiphenoyl (HHDP, Fig. 1b) group formed is a basic structure for the majority of the ET monomers (Okuda et al. 2000; Yoshida et al. 2010). This structure can be further oxidized to first form the dehydrohexahydroxydiphenoyl (DHHDP, Fig. 1b) group and subsequently the transformed DHHDP group, for example, chebuloyl group (Fig. 1b; Okuda et al. 2000; Yoshida et al. 2010). Alternatively, the HHDP group may be coupled with another galloyl group to form the nonahydroxytriphenoyl (NHTP) group (Fig. 1b) characteristic to C-glycosidic ETs with an open glucose core. FlavanoETs, in turn, are complex combinations of C-glycosidic ETs and flavan-3-ol unit(s) (Khanbabaee and van Ree 2001; Yoshida et al. 2010). The structural diversity of ETs is further complicated by the oxidization of the monomeric ETs into larger oligomeric forms (
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