Δ-Keto-acid/hydroxy-lactone isomerization in some lichen depsides, depsidones and diphenyl ethers.

In some compounds in lichens, the carboxylic acid is ortho-substituted by an 2-oxoalkyl chain. This particular structure induces the existence of δ-keto-acid ka or hydroxy-lactone hl isomers, clearly identified by their NMR data and chemical properties, such as dehydration, methylation and behaviour in thermal conditions. Internal hydrogen bonding between the carboxylic acid and substituent in the ortho' position is proposed as an isomerization modulator: an H-bond acceptor (OCH3) leads to ka isomers, whereas hl isomers are obtained with an H-bond donor (OH).

New insights into the Van Krevelen diagram: Automated molecular formula determination from HRMS for a large chemical profiling of lichen extracts.

INTRODUCTION: In recent years, LC-MS has become the golden standard for metabolomic studies. Indeed, LC is relatively easy to couple with the soft electrospray ionization. As a consequence, many tools have been developed for the structural annotation of tandem mass spectra. However, it is sometimes difficult to do data-dependent acquisition (DDA), especially when developing new methods that stray from the classical LC-MS workflow. OBJECTIVE: An old tool from petroleomics that has recently gained popularity in metabolomics, the Van Krevelen diagram, is adapted for an overview of the molecular diversity profile in lichens through high-resolution mass spectrometry (HRMS). METHODS: A new method is benchmarked against the state-of-the-art classification tool ClassyFire using a database containing most known lichen metabolites (n ≈ 2,000). Four lichens known for their contrasted chemical composition were selected, and extractions with apolar, aprotic polar, and protic polar solvents were performed to cover a wide range of polarities. Extracts were analyzed with direct infusion electrospray ionization mass spectrometry (DI-ESI-MS) and atmospheric solids analysis probe mass spectrometry (ASAP-MS) techniques to be compared with the chemical composition described in the literature. RESULTS: The most common lichen metabolites were efficiently classified, with more than 90% of the molecules in some classes being matched with ClassyFire. Results from this method are consistent with the various extraction protocols in the present case study. CONCLUSION: This approach is a rapid and efficient tool to gain structural insight regarding lichen metabolites analyzed by HRMS without relying on DDA by LC-MS/MS analysis. It may notably be of use during the development phase of novel MS-based metabolomic approaches.

ASAP-MS and DART-MS as ancillary tools for direct analysis of the lichen metabolome.

INTRODUCTION: Lichens contain unique metabolites that most often need to be characterized from a limited amount of material. While thin layer chromatography is still the preferred analysis method for most lichenologists, liquid chromatography gives a deeper insight in the lichen metabolome, but an extractive step is needed before any analysis. Therefore, ambient ionization mass spectrometry (MS) analysis of lichen samples using Atmospheric Solid Analysis Probe (ASAP) and Direct Acquisition in Real Time (DART) techniques is evaluated. OBJECTIVE: We looked for a faster method to screen the metabolome by disrupting the classical workflow of analysis. METHODS: Four lichens selected for their metabolic diversity were analyzed with MS; namely Evernia prunastri, Lichina pygmaea, Parmelia saxatilis, and Roccella fuciformis. ASAP and DART analyses were compared against the reference electrospray ionization with a bioinformatic process including Van Krevelen diagrams as well as the multivariate comparison of the ionization methods in positive and negative modes. RESULTS: Metabolite profiles obtained from DART and ASAP analyses of lichen samples are consistent with classical analyses of lichen extracts. Through an easy and rapid experiment and without any extraction solvent, a large and informative profile of lichen metabolites is obtained when using complementary ionization modes of these high resolution mass spectrometry methods. CONCLUSION: ASAP-MS and DART-MS are two ancillary methods that provide a comprehensive evaluation of the lichen metabolome.

Novel Antifungal Compounds, Spermine-Like and Short Cyclic Polylactates, Produced by Lactobacillus harbinensis K.V9.3.1Np in Yogurt.

Lactobacillus harbinensis K.V9.3.1Np was described as endowed with high antifungal activity. Most of the studies associated this activity to the produced organic acids, i.e., lactic acid, acetic acid, and hexanoic acid. The aim of this study was to purify and identify, other not yet described, antifungal molecules produced by L. harbinensis K.V9.3.1Np when used in yogurt fermentation. Active compounds were extracted through several extraction processes using organic solvents and protein precipitation. The fractions of interest were purified using flash chromatography and preparative HPLC for specific characterization. The bioactive compounds identification was performed using Nuclear Magnetic Resonance and Mass Spectrometry. Activity tests against Penicillium expansum and Yarrowia lipolytica showed that the active compounds from L. harbinensis K.V9.3.1Np are benzoic acid and a polyamine identified as a spermine analog, which has not been reported earlier. However, the highest activity was shown by a mixture of short (n = 2-5) polycyclic lactates. Our overall results demonstrate the efficiency of the proposed extraction/purification approach. The new compounds described here have promising antifungal activities but further studies are still needed to decipher their mode of action and production pathways. Even though, they present an interesting potential application in food, feed, as well as, in pharmaceutical industries and could serve as alternative to chemical additives.

Solventless and Metal-Free Synthesis of High-Molecular-Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines.

The solventless reaction of diisopropylaminoborane with n-butylamine, at room temperature, leads to a mixture of B(sp2) H-, B(sp3) H2 -, and B(sp3) H3 -containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high-mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal-free access to high-molecular-mass polyaminoboranes in good to high yields under mild reaction conditions.

Chemical analysis of the Alphaproteobacterium strain MOLA1416 associated with the marine lichen Lichina pygmaea.

Alphaproteobacterium strain MOLA1416, related to Mycoplana ramosa DSM 7292 and Chelativorans intermedius CC-MHSW-5 (93.6% 16S rRNA sequence identity) was isolated from the marine lichen, Lichina pygmaea and its chemical composition was characterized by a metabolomic network analysis using LC-MS/MS data. Twenty-five putative different compounds were revealed using a dereplication workflow based on MS/MS signatures available through GNPS (https://gnps.ucsd.edu/). In total, ten chemical families were highlighted including isocoumarins, macrolactones, erythrinan alkaloids, prodiginines, isoflavones, cyclohexane-diones, sterols, diketopiperazines, amino-acids and most likely glucocorticoids. Among those compounds, two known metabolites (13 and 26) were isolated and structurally identified and metabolite 26 showed a high cytotoxic activity against B16 melanoma cell lines with an IC50 0.6 ± 0.07 µg/mL.

Evidence of a tetradocosahexaenoic cardiolipin in some marine bivalves.

Separation of phospholipid classes in lipid extracts from the scallop Pecten maximus, the Pacific oyster Crassostrea gigas, and the blue mussel Mytilus edulis was conducted using HPLC. An isolated polar lipid fraction was found to contain a very high level of DHA, up to 80 mol% of the total FA. MS with electrospray ionization in the positive-ion mode, tandem MS (MS-MS) and multidimensional NMR spectroscopy were used to analyze the detailed chemical structure of this polar lipid fraction. The isolated fraction contained exclusively cardiolipin (CL) molecules, predominantly in a form with four docosahexaenoyl chains (Do4CL). To the best of our knowledge, this is the first time that such a CL form has been analytically characterized and described in these three bivalve species. This tetradocosahexaenoic CL is presumed to reflect a specific adaptation in bivalves that enhances the structural and functional mechanisms of biomembranes in response to variations in environmental conditions (temperature, salinity, emersion).