New Developments of Laser Desorption Ionization Mass Spectrometry in Natural Products Research

Mass spectrometry (MS) represents an indispensable tool for the structural identification of natural products (NPs) and is one of the major focus areas of analytical chemistry research. The technique has long been used to obtain molecular weights and further molecular formulae. In the past, former ionization sources such as electronic impact (EI) limited MS analysis to predominately volatile, polar, and thermostable compounds. However, the development of soft ionization techniques such as electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and laser desorption/ionization (LDI) have gradually extended the scope of MS analysis to a much wider range of chemical entities. Moreover, the hyphenation of liquid and gas chromatography with MS (LC‐MS, GC‐MS) has provided a most powerful tool for the analysis of complex mixtures and NPs. In fact, LC‐MS is often considered as a method of first choice particularly when studying complex mixtures of small molecules. On the other hand, recent developments in matrix‐assisted laser desorption/ionization (MALDI) and LDI may provide useful supplements and potential alternatives to this approach. Both methods share similar, though slightly different ionization mechanisms. While MALDI uses small molecules comprising strong UV chromophores (matrices) to transfer laser energy to the sample material, LDI targets compounds that can be directly ionized by laser irradiation without any matrix support. Moreover, certain compounds showing LDI properties may also work as MALDI matrices. With regard to NPs research, MALDI and LDI may help overcoming certain limitations encountered in LC‐MS such as the indispensable use of buffer solutions when analyzing alkaloids. Moreover, as (MA)LDI hardly requires any sample conditioning, analysis time can be significantly shortened. With all this in mind, the subsequent article will highlight some interesting MALDI and LDI applications, which focus on the detection of NPs in complex mixtures. This includes the use of specifically adapted matrices for the selective detection of alkaloids (i), the study of the inherent LDI and matrix properties of phenolic compounds (ii) as well of evaluation on the reproducibility of LDI signal patterns (iii). Eventually, a statistical approach toward LDI profiling, which may provide a future tool for quality control of large sample batches will be presented (iv)

Semisynthetic modifications of δ-amplexichromanol, an original tocotrienol with antitumoral properties

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New Developments of Laser Desorption Ionization Mass Spectrometry in Plant Analysis

The structural identification of natural products is one of the major focus areas of analytical chemistry research. Mass spectrometry (MS) has long been used to obtain molecular weights and further molecular formulae. In the past, former ionization sources such as electronic impact unfortunately limited MS analysis to predominately volatile, polar, and thermostable compounds. However, recent developments in soft ionization techniques such as electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), or laser desorption/ionization (LDI) have gradually extended MS analysis to a much wide range of chemical structures. As far as small natural compounds are concerned, LDI sources are still seldom used because of specific technical limitations. Indeed, the photoionization process of LDI is generally assisted by a matrix, which is a small molecule carrying strong UV chromophore. The process is then called matrix‐assisted laser desorption/ionization (MALDI) process. MALDI ionization therefore induces the formation of numerous matrix ions that commonly appear in the range 0–600 Da, and consequently interfere with molecular ions originating from many natural products. For this reason, the correct signal assignment is highly impaired in the critical region of interest. As LDI and MALDI are not only soft ionization processes but also quite sensitive techniques yielding high resolution spectra when coupled to a time‐of‐flight (TOF) analyzer, different attempts have been made to adapt these techniques for the analysis of natural products. Three of them will be more specifically discussed in this chapter: (i) LDI on neat gold surfaces obtained by physical vapor diffusion (PVD), (ii) desorption/ionization on self‐assembled monolayer surfaces (DIAMS), and (iii) the use of specific matrices for the selective detection of alkaloids

New Use for a Compound as a Matrix in the Specific Detection, Identification and/or Quantification of Alkaloids by MALDI-TOF Mass Spectrometry

The present invention relates to (i) a method of analysing small molecules that may have a mass of < 800 Da, in particular alkaloids, said method being generally referred to as MALDI-TOF-MS (or MALDI Time-of-Flight MAss Spectrometry) which is an acronym for a method of analysis by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, to (ii) a molecule according to formula (I) and to the use thereof as a matrix in such an analysis method

Novel Cytotoxic 4-Phenylfuranocoumarins from Calophyllum dispar

Eight new 4-phenylfuranocoumarins (1−8) have been isolated from the stem bark and the fruits of Calophyllum dispar, together with three known coumarins. The structures of 1−8 were established by means of spectroscopic analysis, including extensive 2D NMR studies. Some of these furanocoumarins exhibited significant cytotoxic activity against KB cells

Studies on the reactivity of a tertiary allylic alcohol in an acetophenonic series, a model for natural products synthesis

The synthesis of benzopyranic simplified analogues of dibenzopyranic natural compounds is described, together with the access to a precursor of a new furobenzopyranic natural product. These natural products have anti-cancer activity. The 1,3-diacetoxy-2-acetyl-4-(3-hydroxy-3-methylbut-1-enyl)benzene synthone is used as a common precursor to these structures

Front face fluorescence spectroscopy and visible spectroscopy coupled with chemometrics have the potential to characterise ripening of Cabernet Franc grapes

The potential of front-face spectroscopy for grape ripening dates discrimination was investigated on Cabernet Franc grapes from three parcels located on the Loire Valley and for six ripening dates. The 18 batches were analysed by front-face fluorescence spectroscopy and visible spectroscopy. The excitation spectra (250–310 nm, emission wavelength = 350 nm) were characterised by a shoulder at 280 nm. Grapes spectra were classified by factorial discriminant analysis (FDA). Ripening dates were well predicted by fluorescence spectra: grapes before veraison were separated from grapes after veraison and almost every ripening date was identified. The common spectroscopic space obtained by CCSWA showed that wavelengths corresponding to anthocyanin absorption in the visible were correlated to fluorescence wavelengths around the starting and ending points of the shoulder (263 and at 292 nm). Then, regression models were investigated to predict total soluble solids (TSS), total acidity, malvidin-3G, total anthocyanins and total phenolics content from visible and fluorescence spectra. To predict technological indicators (TSS and total acidity), the PLS model with visible spectra (RMSECV = 0.82°Brix or 0.96 g L−1 H2SO4) was better than those with fluorescence one (RMSECV = 1.39°Brix or 2.06 g L−1 H2SO4). For malvidin-3G and total anthocyanins, all R c 2 and R cv 2 were superior to 0.90 and RMSECV were low. Visible and fluorescence spectroscopies succeeded in predicting anthocyanin content. Concerning total phenolic, the best prediction was provided by fluorescence spectroscopy