Structure of Echivulgarine, a Pyrrolizidine Alkaloid Isolated from the Pollen of Echium vulgare

Soil pH, developmental stages and geographical origin differently influence the root metabolomic diversity and root-related microbial diversity of Echium vulgare from native habitats

Improved understanding of the complex interaction between plant metabolism, environmental conditions and the plant-associated microbiome requires an interdisciplinary approach: Our hypothesis in our multiomics study posited that several environmental and biotic factors have modulating effects on the microbiome and metabolome of the roots of wild Echium vulgare plants. Furthermore, we postulated reciprocal interactions between the root metabolome and microbiome. We investigated the metabolic content, the genetic variability, and the prokaryotic microbiome in the root systems of wild E. vulgare plants at rosette and flowering stages across six distinct locations. We incorporated the assessment of soil microbiomes and the measurement of selected soil chemical composition factors. Two distinct genetic clusters were determined based on microsatellite analysis without a consistent alignment with the geographical proximity between the locations. The microbial diversity of both the roots of E. vulgare and the surrounding bulk soil exhibited significant divergence across locations, varying soil pH characteristics, and within the identified plant genetic clusters. Notably, acidophilic bacteria were characteristic inhabitants of both soil and roots under acidic soil conditions, emphasizing the close interconnectedness between these compartments. The metabolome of E. vulgare significantly differed between root samples from different developmental stages, geographical locations, and soil pH levels. The developmental stage was the dominant driver of metabolome changes, with significantly higher concentrations of sugars, pyrrolizidine alkaloids, and some of their precursors in rosette stage plant roots. Our study featured the complex dynamics between soil pH, plant development, geographical locations, plant genetics, plant metabolome and microbiome, shedding light on existing knowledge gaps.

Vincazalidine A, a unique bisindole alkaloid from Catharanthus roseus

A new dimeric indole alkaloid, vincazalidine A consisting of an aspidosperma type and a modified iboga type with 1-azatricyclo ring system consisting of one azepane and two piperidine rings coupled with an oxazolidine ring was isolated from Catharanthus roseus, and the structure including absolute stereochemistry was elucidated on the basis of spectroscopic data as well as DP4 statistical analysis. Vincazalidine A induced G2 arrest and subsequent apoptosis in human lung carcinoma cell line, A549 cells.

Isovincathicine from Catharanthus roseus induces apoptosis in A549 cells

A dimeric indole alkaloid, isovincathicine consisting of an aspidosperma type and modified iboga with C-7-C-20 connection type skeletons was first isolated from Catharanthus roseus, and the structure including stereochemistry was elucidated on the basis of spectroscopic data as well as DP4 statistical analysis. Isovincathicine inhibited cell proliferation in A549 cells. We investigated the detailed mode of action of isovincathicine-induced inhibitory effects on cell proliferation in A549 cells. Flow cytometric analysis showed that isovincathicine-treated cells accumulated in the G2 phase after 24 h, and the percentage of cells showing cell death increased after 48 h. Western blotting also showed increased expression of BimEL, an apoptosis-related protein, and decreased expression of Mcl-1 and Bcl-xL. Isovincathicine was suggested to induce apoptosis in A549 cells by a mechanism is similar to that of vinblastine.

Advanced Methods for Natural Products Discovery: Bioactivity Screening, Dereplication, Metabolomics Profiling, Genomic Sequencing, Databases and Informatic Tools, and Structure Elucidation

Natural Products (NP) are essential for the discovery of novel drugs and products for numerous biotechnological applications. The NP discovery process is expensive and time-consuming, having as major hurdles dereplication (early identification of known compounds) and structure elucidation, particularly the determination of the absolute configuration of metabolites with stereogenic centers. This review comprehensively focuses on recent technological and instrumental advances, highlighting the development of methods that alleviate these obstacles, paving the way for accelerating NP discovery towards biotechnological applications. Herein, we emphasize the most innovative high-throughput tools and methods for advancing bioactivity screening, NP chemical analysis, dereplication, metabolite profiling, metabolomics, genome sequencing and/or genomics approaches, databases, bioinformatics, chemoinformatics, and three-dimensional NP structure elucidation.

Structural characterisation of natural products by means of quantum chemical calculations of NMR parameters: new insights

In this review, we focus in all aspects of NMR simulation of natural products, from the fundamentals to the new computational toolboxes available, combining advanced quantum chemical calculations with upstream data processing and machine learning.

Pyrrolizidine Alkaloids of Blue Heliotrope (Heliotropium amplexicaule) and Their Presence in Australian Honey

Blue heliotrope (Heliotropium amplexicaule) is an invasive environmental weed that is widely naturalized in eastern Australia and has been implicated as a source of pyrrolizidine alkaloid (PA) poisoning in livestock. Less well-documented is the potential of such carcinogenic alkaloids to contaminate honey from bees foraging on this plant species. In this study, the PA profile of H. amplexicaule plant material, determined by HRAM LC-MS/MS, revealed the presence of nine PAs and PA-N-oxides, including several PAs and PA-N-oxides of the indicine class, which have not previously been reported. The predominant alkaloid, indicine, represents 84% of the reduced PA content, with minor alkaloids identified as intermedine and the newly reported helioamplexine, constituting 7 and 9%, respectively. NMR analysis confirmed the identity of helioamplexine as a previously unreported indicine homologue. This is the first report of the isolation of intermedine, helioamplexine, and 3'-O-angelylindicine from H. amplexicaule. Also described is the identification of N-chloromethyl analogues of the major alkaloids as isolation-derived artifacts from reactions with dichloromethane. Analysis of regional-market honey samples revealed a number of honey samples with PA profiles analogous to that seen in H. amplexicaule, with measured PA contents of up to 2.0 μg of PAs per gram of honey. These results confirm the need for honey producers to be aware of H. amplexicaule as a potential PA source, most particularly in products where honey is sourced from a single location.

Pyrrolizidine Alkaloids: The Botanical Origin of Pollen Collected during the Flowering Period of Echium vulgare and the Stability of Pyrrolizidine Alkaloids in Bee Bread

Previous studies have shown that pollen products sold as nutritional supplements and used in apitherapy may contain toxic pyrrolizidine alkaloids (PAs) if bees collect pollen from PA-containing plants, such as Echium vulgare. In this study, the botanical origin of pollen from two observation sites was studied. Despite a high PA content in pollen samples that bees collected during E. vulgare's flowering period, bees were found to collect relatively few Echium pollen loads. Thus, the monitoring of pollen loads collected at the apiaries is unviable to estimate the risk of PA contamination in pollen or bee bread. In a second step, the stability of PAs in bee bread samples containing PAs at concentrations of 2538 ng/g and 98 ng/g was assessed over a period of five or six months, respectively. No significant PA reduction was observed in bee bread stored at 15 °C, but there were overall PA reductions of 39% and 33% in bee bread stored at 30 °C, reflecting hive conditions. While PA N-oxides decreased over time, other types of PAs remained relatively stable. Monitoring PAs in pollen products remains important to ensure consumer safety and should include echivulgarine (and its N-oxide), the major PA type found in pollen from E. vulgare.

Pyrrolizidine alkaloids: occurrence, biology, and chemical synthesis

Covering: 2013 up to the end of 2015This review covers the isolation and structure of new pyrrolizidines; pyrrolizidine biosynthesis; biological activity, including the occurrence of pyrrolizidines as toxic components or contaminants in foods and beverages; and formal and total syntheses of naturally-occurring pyrrolizidine alkaloids and closely related non-natural analogues.