Abstract
Desorption atmospheric pressure photoionization (DAPPI) is an ambient mass spectrometry (MS) technique that allows the analysis of both polar and nonpolar compounds directly from the surfaces of various sample types. Here, DAPPI was used to study the chemical profiles in different parts of birch and alder tree barks. Four distinct fractions of Betula pendula (silver birch) bark were collected from three different developmental stages of the stem, after which the chemical profiles of the different tissue types were measured. Of special interest were triterpenoids, a class of important defensive substances, which are found in the bark of the silver birch. Additionally, the chemical profiles of lenticels and the surrounding surfaces in the phellem of B. pendula (silver birch), Alnus glutinosa (black alder), and Alnus incana (gray alder) were screened with DAPPI. Another ambient MS technique, laser ablation atmospheric pressure photoionization (LAAPPI), was further used for the mass spectrometry imaging of lenticels on the B. pendula phellem. All the studied birch bark fractions showed individual chemical profiles in DAPPI. The mass spectra from the young apical stem and the transition zone resembled each other more than the mature stem. Instead, the phellem was found to contain a high amount of triterpenoids in all the developmental stages of the stem. The most intense peaks in the DAPPI mass spectra of the birch bark fractions were those of betulin and lupeol. Betulinic and betulonic acid peaks were intense as well, and these compounds were detected especially in the lenticels of the tree samples.Graphical abstract
Highlights
Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.It has been reported that over 50% of currently sold pharmaceuticals originate from natural products or naturally occurring compounds or their derivatives synthesized in the laboratory [1]
The most intense signals were observed for betulin, lupeol, and betulinic acid, which were detected as M+ ions at m/z 442, 426, and 456, respectively
Triterpenoids and other plant metabolites were detected from B. pendula bark fractions collected from three different developmental stages of the tree
Summary
One natural compound that has proved to have interesting bioactivities is the triterpenoid betulin, and especially its natural derivatives like betulinic acid [2,3,4]. These compounds have been used as scaffolds in various drug development projects that aim at treatments of, e.g., bacterial inflammations [5] and cancer [6]. A schematic picture of the B. pendula bark structure containing four fractions (phellem, phelloderm/ phellogen, old phloem, and developing phloem) is presented in
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