Unusual negative charge-directed fragmentation: collision-induced dissociation of cyclopentenone oxylipins in negative ion mode

Triterpene Glycosides from the Viscera of Sea Cucumber Apostichopus japonicus with Embryotoxicity

Sea cucumbers release chemical repellents from their guts when they are in danger from predators or a hostile environment. To investigate the chemical structure of the repellent, we collected and chemically analyzed the viscera of stressed sea cucumbers (Apostichopus japonicus) in the Yellow Sea of China. Two undescribed triterpene glycosides (1 and 2), together with a known cladoloside A (3), were identified and elucidated as 3β-O-{2-O-[β-d-quinovopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (1), 3β-O-{2-O-[β-d-glucopyranosyl]-4-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-glucopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (2), 3β-O-{2-O-[3-O-methyl-β-d-glucopyranosyl-(1→3)-β-d-xylopyranosyl-(1→4)-β-d-quinovopyranosyl]-β-d-xylopyranosyl}-holosta-9(11),25(26)-dien-16-one (3) by spectroscopic analysis, including HR-ESI-MS and NMR spectra. Compounds 1, 2, and 3 display embryonic toxicity, as indicated by their 96-hour post-fertilization lethal concentration (96 hpf-LC50) values of 0.289, 0.536, and 0.091 μM, respectively. Our study discovered a class of triterpene glycoside compounds consisting of an oligosaccharide with four sugar units and a holostane aglycone. These compounds possess embryotoxicity and may serve as chemical defense molecules in marine benthic ecosystems.

Sea Cucumber Viscera Contains Novel Non-Holostane-Type Glycoside Toxins that Possess a Putative Chemical Defense Function

Sea cucumbers frequently expel their guts in response to predators and an aversive environment, a behavior perceived as releasing repellents involved in chemical defense mechanisms. To investigate the chemical nature of the repellent, the viscera of stressed sea cucumbers (Apostichopus japonicus) in the Yellow Sea of China were collected and chemically analyzed. Two novel non-holostane triterpene glycosides were isolated, and the chemical structures were elucidated as 3ꞵ-O-[ꞵ-D-glucopyranosyl-(1→2)-ꞵ-D-xylopyranosyl]-(20S)-hydroxylanosta-7,25-diene-18(16)-lactone (1) and 3ꞵ-O-[ꞵ-D-quinovopyranosyl-(1→2)-ꞵ-D-xylopyranosyl]-(20S)-hydroxylanosta-7,25-diene-18(16)-lactone (2) by spectroscopic and mass-spectrometric analyses, exemplifying a triterpene glycoside constituent of an oligosaccharide containing two sugar-units and a non-holostane aglycone. Zebrafish embryos were exposed to various doses of 1 and 2 from 4 to 96 hpf. Compound 1 exposure showed 96 h-LC50 41.5 µM and an increased zebrafish mortality rates in roughly in a dose- and time-dependent manner. Compound 2, with different sugar substitution, exhibited no mortality and moderate teratogenic toxicity with a 96 h-EC50 of 173.5 µM. Zebrafish embryos exhibited teratogenic effects, such as reduced hatchability and total body length. The study found that triterpene saponin from A. japonicus viscera had acute toxicity in zebrafish embryos, indicating a potential chemical defense role in the marine ecosystem.

Male lake char release taurocholic acid as part of a mating pheromone

The evolutionary origins of sexual preferences for chemical signals remain poorly understood, due, in part, to scant information on the molecules involved. In the current study, we identified a male pheromone in lake char (Salvelinus namaycush) to evaluate the hypothesis that it exploits a non-sexual preference for juvenile odour. In anadromous char species, the odour of stream-resident juveniles guides migratory adults into spawning streams. Lake char are also attracted to juvenile odour but have lost the anadromous phenotype and spawn on nearshore reefs, where juvenile odour does not persist long enough to act as a cue for spawning site selection by adults. Previous behavioural data raised the possibility that males release a pheromone that includes components of juvenile odour. Using metabolomics, we found that the most abundant molecule released by males was also released by juveniles but not females. Tandem mass spectrometry and nuclear magnetic resonance were used to identify the molecule as taurocholic acid (TCA), which was previously implicated as a component of juvenile odour. Additional chemical analyses revealed that males release TCA at high rates via their urine during the spawning season. Finally, picomolar concentrations of TCA attracted pre-spawning and spawning females but not males. Taken together, our results indicate that male lake char release TCA as a mating pheromone and support the hypothesis that the pheromone is a partial match of juvenile odour.

Acute Toxicity of the Dinoflagellate Amphidinium carterae on Early Life Stages of Zebrafish (Danio rerio)

Dinoflagellates of the genus Amphidinium can produce a variety of polyketides, such as amphidinols (AMs), amphidinoketides, and amphidinin, that have hemolytic, cytotoxic, and fish mortality properties. AMs pose a significant threat to ecological function due to their membrane-disrupting and permeabilizing properties, as well as their hydrophobicity. Our research aims to investigate the disparate distribution of AMs between intracellular and extracellular environments, as well as the threat that AMs pose to aquatic organisms. As a result, AMs containing sulphate groups such as AM19 with lower bioactivity comprised the majority of A. carterae strain GY-H35, while AMs without sulphate groups such as AM18 with higher bioactivity displayed a higher proportion and hemolytic activity in the extracellular environment, suggesting that AMs may serve as allelochemicals. When the concentration of extracellular crude extracts of AMs reached 0.81 µg/mL in the solution, significant differences in zebrafish embryonic mortality and malformation were observed. Over 96 hpf, 0.25 μL/mL of AMs could cause significant pericardial edema, heart rate decrease, pectoral fin deformation, and spinal deformation in zebrafish larvae. Our findings emphasized the necessity of conducting systematic research on the differences between the intracellular and extracellular distribution of toxins to gain a more accurate understanding of their effects on humans and the environment.

Unique localization of jasmonic acid-related compounds in developing Phaseolus vulgaris L. (common bean) seeds revealed through desorption electrospray ionization-mass spectrometry imaging

Jasmonic acid (JA) and its precursors are oxylipins derived from α-linolenic acid (αLA). Presumably, they are involved in the regulation of seed embryogenesis, dormancy, and germination. However, their spatial localization in the developing Phaseolus vulgaris L. (common bean) seeds has not been fully elucidated. Therefore, desorption electrospray ionization-mass spectrometry imaging (DESI-MSI) was performed to investigate their localization in the developing seeds. Peaks corresponding to the chemical formulae of αLA and 3-oxo-2-(2-(Z)-pentenyl)-cyclopentane-1-octanoic acid (OPC-8:0) were localized mainly in the radicle and seed coat, while that of 12-oxo-phytodienoic acid (OPDA) in the seed coat. This was consistent with the quantitative results obtained using liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) analysis. In contrast, DESI-tandem MSI (MS/MSI) and LC-ESI-MS/MS analyses showed that the effects of isomers on the DESI-MSI ion images were small for αLA and OPDA, but not for OPC-8:0. This indicated that DESI-MSI could accurately visualize αLA and OPDA, while DESI-MS/MSI was necessary to visualize OPC-8:0. The results demonstrated that free αLA and OPC-8:0 were abundant in the radicle and seed coat, while free OPDA was accumulated in the seed coat. Interestingly, the localization pattern of OPDA was similar to that of JA. In addition, compared to the concentrations of OPDA, the concentration of OPC-8:0 was lower in the seed coat and higher in the radicle. These results suggest that OPDA and/or JA play a biological role mainly in the seed coat, while OPC-8:0 is biologically active mainly in the radicle. Therefore, DESI-MSI coupled with LC-ESI-MS is a useful tool for spatial analysis of JA-related compounds in developing common bean seeds.

Ultrasound-Assisted Extraction Optimization of α-Glucosidase Inhibitors from Ceratophyllum demersum L. and Identification of Phytochemical Profiling by HPLC-QTOF-MS/MS

Ceratophyllum demersum L. (CDL) is a traditional Chinese herb to treat many diseases, but research on its anti-diabetic activity is not available. In this research, the α-glucosidase inhibitory ability and phytochemical constituents of CDL extract were firstly studied. Optimal ultrasound-assisted extraction conditions for α-glucosidase inhibitors (AGIs) were optimized by single factor experiment and response surface methodology (RSM), which was confirmed as 70% methanol, liquid-to-solid ratio of 43 (mL/g), extraction time of 54 min, ultrasonic power of 350 W, and extraction temperature of 40 °C. The lowest IC₅₀ value for α-glucosidase inhibition was 0.15 mg dried material/mL (mg DM/mL), which was much lower than that of acarbose (IC₅₀ value of 0.64 mg DM/mL). In total, 80 compounds including 8 organic acids, 11 phenolic acids, 25 flavonoids, 21 fatty acids, and 15 others were identified or tentatively identified from CDL extract by HPLC-QTOF-MS/MS analysis. The results suggested that CDL could be a potential source of α-glucosidase inhibitors. It can also provide useful phytochemical information for research into other bioactivities.

Charge migration fragmentation in the negative ion mode of cyclopentenone and cyclopentanone intermediates in the biosynthesis of jasmonates

RATIONALE

Jasmonates are formed from 12-oxo-10,15(Z)-phytodienoic acid (12-OPDA) in plants and also from 12-oxo-10-phytoenoic acid (12-OPEA) in fungi. Collision-induced dissociation (CID) of [M-H]^- generates characteristic product anions at m/z 165 [C₁₁ H₁₇ O]^- . Our goal was to investigate the structure and mode of formation of this anion by CID of 12-OPDA, 12-OPEA, and 12-oxophytonoic acid (12-OPA).

METHODS

We investigated the CID of the [M-H]^- , [M-H-CO₂ ]^- , and [M-H-H₂ O]^- anions using electrospray ionization and MS/MS analysis of 12-OPDA, 12-OPEA, and 12-OPA, and compared the results with the data obtained with the corresponding compounds labeled with ² H at C-6 and C-7 and with structural and side chain analogs.

RESULTS

CID of [6,6,7,7-² H₄ ]12-OPEA and [6,6-² H₂ ]12-OPDA ([M-H]^- and [M-H-CO₂ ]^- ) showed that one or two ² H atoms were transferred to anions at m/z 165 as judged by the signal intensities of m/z 165 + 1 or 165 + 2, respectively. CID of [6,6-² H₂ ]- and [6,6,7,7-² H₄ ]-12-OPA ([M-H]^- and [M-H-CO₂ ]^- ) yielded the loss of H₂ from the cyclopentanone and displayed the transfer of one ² H atom in analogy to 12-OPEA. In contrast, CID of [6,6,7,7-² H₄ ]12-OPEA and [6,6,7,7-² H₄ ]12-OPA [M-H-H₂ O]^- demonstrated the transfer of two ² H atoms (m/z 165 + 2). All spectra obtained by CID of [6,6,7,7-² H₄ ]12-OPDA and [6,6,7,7-² H₄ ]12-oxo-9(13),15(Z)-phytodienoic acid showed that one or two additional ² H atoms could be transferred to this anion at m/z 167 of [6,6-² H₂ ]12-OPDA due to isotope scrambling.

CONCLUSIONS

CID of 12-OPDA and 12-OPEA generates cyclopentanone enolate anions at m/z 165 by charge-driven hydride transfer as a common mechanism and by bond cleavage between C-7 and C-8 of the carboxyl side chains with either gain or loss of a hydrogen atom.

Quantitative Jasmonate Profiling Using a High-Throughput UPLC-NanoESI-MS/MS Method

Jasmonic acid (JA) and its many derivatives-collectively referred as jasmonates-occur ubiquitously in land plants and regulate a wide range of stress-responses and development. Measuring these signaling compounds is complicated by the large number of jasmonate derivatives and the comparatively low concentration of these metabolites in plant tissues. We, here, present a selective and sensitive method consisting of a two-phase extraction coupled with liquid chromatography, nanoelectrospray ionization, and mass spectrometry to determine jasmonate levels in tissues and fluids of various plant species. The application of stable deuterium-labelled standards in combination with authentic standards allows the absolute quantification of a multitude of jasmonates and, additionally, the semi-quantitative analysis of further metabolites from the jasmonate pathway.

An allene oxide and 12-oxophytodienoic acid are key intermediates in jasmonic acid biosynthesis by Fusarium oxysporum

Fungi can produce jasmonic acid (JA) and its isoleucine conjugate in large quantities, but little is known about the biosynthesis. Plants form JA from 18:3n-3 by 13S-lipoxygenase (LOX), allene oxide synthase, and allene oxide cyclase. Shaking cultures of Fusarium oxysporum f. sp. tulipae released over 200 mg of jasmonates per liter. Nitrogen powder of the mycelia expressed 10R-dioxygenase-epoxy alcohol synthase activities, which was confirmed by comparison with the recombinant enzyme. The 13S-LOX of F. oxysporum could not be detected in the cell-free preparations. Incubation of mycelia in phosphate buffer with [17,17,18,18,18-²H₅]18:3n-3 led to biosynthesis of a [²H₅]12-oxo-13-hydroxy-9Z,15Z-octadecadienoic acid (α-ketol), [²H₅]12-oxo-10,15Z-phytodienoic acid (12-OPDA), and [²H₅]13-keto- and [²H₅]13S-hydroxyoctadecatrienoic acids. The α-ketol consisted of 90% of the 13R stereoisomer, suggesting its formation by nonenzymatic hydrolysis of an allene oxide with 13S configuration. Labeled and unlabeled 12-OPDA were observed following incubation with 0.1 mM [²H₅]18:3n-3 in a ratio from 0.4:1 up to 47:1 by mycelia of liquid cultures of different ages, whereas 10 times higher concentration of [²H₅]13S-hydroperoxyoctadecatrienoic acid was required to detect biosynthesis of [²H₅]12-OPDA. The allene oxide is likely formed by a cytochrome P450 or catalase-related hydroperoxidase. We conclude that F. oxysporum, like plants, forms jasmonates with an allene oxide and 12-OPDA as intermediates.

Optimized Jasmonic Acid Production by Lasiodiplodia theobromae Reveals Formation of Valuable Plant Secondary Metabolites

Jasmonic acid is a plant hormone that can be produced by the fungus Lasiodiplodia theobromae via submerged fermentation. From a biotechnological perspective jasmonic acid is a valuable feedstock as its derivatives serve as important ingredients in different cosmetic products and in the future it may be used for pharmaceutical applications. The objective of this work was to improve the production of jasmonic acid by L. theobromae strain 2334. We observed that jasmonic acid formation is dependent on the culture volume. Moreover, cultures grown in medium containing potassium nitrate as nitrogen source produced higher amounts of jasmonic acid than analogous cultures supplemented with ammonium nitrate. When cultivated under optimal conditions for jasmonic acid production, L. theobromae secreted several secondary metabolites known from plants into the medium. Among those we found 3-oxo-2-(pent-2-enyl)-cyclopentane-1-butanoic acid (OPC-4) and hydroxy-jasmonic acid derivatives, respectively, suggesting that fungal jasmonate metabolism may involve similar reaction steps as that of plants. To characterize fungal growth and jasmonic acid-formation, we established a mathematical model describing both processes. This model may form the basis of industrial upscaling attempts. Importantly, it showed that jasmonic acid-formation is not associated to fungal growth. Therefore, this finding suggests that jasmonic acid, despite its enormous amount being produced upon fungal development, serves merely as secondary metabolite.

A previously undescribed jasmonate compound in flowering Arabidopsis thaliana - The identification of cis-(+)-OPDA-Ile

Jasmonates (JAs) are plant hormones that integrate external stress stimuli with physiological responses. (+)-7-iso-JA-L-Ile is the natural JA ligand of COI1, a component of a known JA receptor. The upstream JA biosynthetic precursor cis-(+)-12-oxo-phytodienoic acid (cis-(+)-OPDA) has been reported to act independently of COI1 as an essential signal in several stress-induced and developmental processes. Wound-induced increases in the endogenous levels of JA/JA-Ile are accompanied by two to tenfold increases in the concentration of OPDA, but its means of perception and metabolism are unknown. To screen for putative OPDA metabolites, vegetative tissues of flowering Arabidopsis thaliana were extracted with 25% aqueous methanol (v/v), purified by single-step reversed-phase polymer-based solid-phase extraction, and analyzed by high throughput mass spectrometry. This enabled the detection and quantitation of a low abundant OPDA analog of the biologically active (+)-7-iso-JA-L-Ile in plant tissue samples. Levels of the newly identified compound and the related phytohormones JA, JA-Ile and cis-(+)-OPDA were monitored in wounded leaves of flowering Arabidopsis lines (Col-0 and Ws) and compared to the levels observed in Arabidopsis mutants deficient in the biosynthesis of JA (dde2-2, opr3) and JA-Ile (jar1). The observed cis-(+)-OPDA-Ile levels varied widely, raising questions concerning its role in Arabidopsis stress responses.

Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products

Over the last decade, the number of studies reporting the use of electrospray ionization mass spectrometry (ESI-MS) in combination with collision cells (or other activation methods) to promote fragmentation of synthetic and natural products for structural elucidation purposes has considerably increased. However, the lack of a systematic compilation of the gas-phase fragmentation reactions subjected to ESI-MS/MS conditions still represents a challenge and has led to many misunderstood results in the literature. This review article exploits the most common fragmentation reactions for ions generated by ESI in positive and negative modes using collision cells in an effort to stimulate the use of this technique by non-specialists, undergraduate students and researchers in related areas.