Presently, the key bottleneck of (plant) metabolomics is structural confirmation and elucidation of secondary metabolites.
is a well-established model system to monitor plant-herbivore interactions with metabolomics being
a novel approach to investigate the underlying biology . 17-Hydroxygeranyllinallool diterpene glycosides (HGL-DTGs) are
abundant direct defense compounds with their mode of action being largely unknown [1-3]. New acyclic HGL-DTGs were
characterized using MS and NMR after extraction of several hundred grams of raw plant material [2, 3]. Such scale is not
compatible to the analytical scope of metabolomics. Here, we present novel solutions facilitating the identification and fast
dereplication process of natural products when mass spectral libraries are not yet available and the sample amount is limited.
Plant samples were prepared as described previously . Chromatographic separation was carried out using an UHPLC system
combined with ultra high resolution (UHR) Q-TOF MS detection. Selected plant samples were fractionated. Peaks enriched in
HGL-DTGs were subjected to detailed fragmentation studies by means of direct infusion measurements.
The dereplication of HGL-DTGs is rendered difficult by the large number of in-source fragments and adduct formation,
and their molecular weight of 800-1000m/z. Novel algorithms were applied for deconvolution of LC-MS chromatograms by
correlation analysis to safely determine the molecular ion in the presence of adducts and in-source CID fragments. Molecular
formula determination was carried out by combined evaluation of mass accuracy, isotopic patterns, adduct and fragment
information. The diagnostic fragments for the HGL-DTG backbone and successive sugar units, such as [M+H]
and 417.2999m/z = C
enabled the rapid identification of the entire compound family, which is subsequently
characterized in more detail. For this, the fragmentation results have been combined with the structural information to visualize
the interpretation. Simultaneously the necessary validation prior submission to a mass spectral library is achieved.
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