Abstract
Flavonoids are a group of compounds that are commonly found in various plants, where they play important roles in many processes, including free radical scavenging and UV protection. These compounds can also act as chemical messengers, physiological regulators or protectants against pathogens in the defense reactions of plants. Flavonoid activity is regulated by the addition of various substituents, usually mono- or oligosaccharides of common sugars, such as glucose, rhamnose or galactose. In some plants, glucuronic acid is attached, and this sugar is often acylated by phenylpropanoic acids. Identification of these compounds and their derivatives is of great importance to understanding their role in plant metabolism and defense mechanisms; this research is important because flavonoids are frequently a significant constituent of the human diet. In this study, we identify the flavonoid conjugates present in Axyris amaranthoides L. extracts and demonstrate the usefulness of high-resolution mass spectrometry (HRMS) analyzers for the differentiation of isobaric compounds and the utility of fragmentation spectra for the differentiation of isomeric structures. According to our knowledge, some of the structures, especially dehydrodiferulated conjugates of tricin, whose structures are proposed here have been found for the first time in plant material.
Highlights
Flavonoids are present in plants mainly as glycosides; glucuronides, in which uronic acids occur as sugar units, are less frequent [1]
The use of an LC-MS/MS system comprising a rapid HPLC and a tandem MS/MS spectrometer equipped with a high-resolution time-of-flight analyzer permits the structural characterization of flavonoid glycoconjugates containing glucuronic acid and phenolic acyl substituents
It is of particular importance that mechanisms observed for glycosides containing more than one molecule of glucuronic acid are dramatically different from those of flavonoid glycoconjugates containing sugars without carboxyl groups, especially when using the negative ion mode
Summary
Flavonoids are present in plants mainly as glycosides; glucuronides, in which uronic acids occur as sugar units, are less frequent [1]. High resolution MS was used to identify saponins and flavonoids in Camellia oleifera [34], using a ultra high performance liquid chromatography coupled with electrospray ionization hybrid linear trap quadrupole orbitrap mass spectrometry (UHPLC-LTQ-orbitrap-MSn) system, it was possible to tentatively characterize seven flavonol glycosides, and MS3 spectra were used for unambiguous aglycone characterization Another interesting work showing usefulness of the high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MSn) approach for comprehensive plant metabolites characterization was published by Wang and co-workers [35], where authors propose general strategies for analysis of complex samples. To the best of our knowledge, some ofGlycosides the structures proposed here have been shown for the first time in plants
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