Fast Identification of Radical Scavengers from Securigera varia by Combining 13C-NMR-Based Dereplication to Bioactivity-Guided Fractionation

13C NMR dereplication-assisted isolation of bioactive polyphenolic metabolites from Clusia flava Jacq

Presently it is estimated that many of the approximately 4000 new natural products isolated every year following complicated, long, and expensive isolation processes are already known; because of this, developing new strategies for locating secondary metabolites of interest in complex extracts or fractions is important. Currently, chromatographic and spectroscopic techniques are being used to optimize the isolation and identification of natural products. In this investigation we have used 13C NMR dereplication analyses for the quick identification of a number of triterpenes (friedelin, lupeol, betulinic acid), sterols (euphol, β-sitosterol) and fatty acids (palmitic acid) present in semipurified fractions obtained from the stem bark extract of Clusia flava and to assist in the isolation of the bioactive metabolites trapezifolixanthone and paralycolin A. The complete and correct assignment of the 1H and 13C NMR spectroscopic data for paralycolin A is reported for the first time and the antioxidant and antiAGEs activity of both metabolites is described.

Old Meets New: Mass Spectrometry-Based Untargeted Metabolomics Reveals Unusual Larvicidal Nitropropanoyl Glycosides from the Leaves of Heteropterys umbellata

The Aedes aegypti (Diptera: Culicidae) mosquito is the vector of several arboviruses in tropical and subtropical areas of the globe, and synthetic pesticides remain the most widely used combat strategy. This study describes the investigation of secondary metabolites with larvicidal activity from the Malpighiaceae taxon using a metabolomic and bioactivity-based approach. The workflow initially consisted of a larvicidal screening of 394 extracts from the leaves of 197 Malpighiaceae samples, which were extracted using solvents of different polarity, leading to the selection of Heteropterys umbellata for the identification of active compounds. By employing untargeted mass spectrometry-based metabolomics and multivariate analyses (PCA and PLS-DA), it was possible to determine that the metabolic profiles of different plant organs and collection sites differed significantly. A bioguided approach led to the isolation of isochlorogenic acid A (1) and the nitropropanoyl glucosides karakin (2) and 1,2,3,6-tetrakis-O-[3-nitropropanoyl]-beta-glucopyranose (3). These nitro compounds exhibited larvicidal activity, possibly potentialized by synergistic effects of their isomers in chromatographic fractions. Additionally, targeted quantification of the isolated compounds in different extracts corroborated the untargeted results from the statistical analyses. These results support a metabolomic-guided approach in combination with classical phytochemical techniques to search for natural larvicidal compounds for arboviral vector control.

Analysis of 3-nitropropionic acid in Fabaceae plants by HPLC-MS/MS

INTRODUCTION

3-Nitropropionic acid (3-NPA) is a toxic compound that can accumulate in esterified form in the Fabaceae family. In the Lotae tribe, many species have been identified as 3-NPA producers (e.g., Securigera varia), while some of the genetically close Lotae plants were formerly reported as 3-NPA-free (e.g., Lotus corniculatus and Anthyllis vulneraria). These plants are used as forage and have a tradition in ethnomedicine, also, the extracts of A. vulneraria are used in cosmetics.

OBJECTIVES

Our aim was to investigate the 3-NPA content of these selected Fabaceae species and to develop a validated quantitative method to evaluate 3-NPA concentrations in extracts of different herbal parts and cosmetic products.

MATERIALS AND METHODS

A UHPLC-ESI-Orbitrap-MS/MS method was applied for detection and identification of 3-NPA derivatives in the form of glucose esters. For the quantitative analysis, an optimized sample processing method was developed. The free 3-NPA content was determined using HPLC-ESI-MS/MS.

RESULTS

3-NPA esters could be detected in all three species, but their quantity showed a high variation. S. varia contained 0.5-1.0 g/100 g of 3-NPA, while in L. corniculatus samples only trace quantities were detectable, below the LOQ (25 ng/ml). Most of the A. vulneraria samples showed similarly low concentrations, but one sample had 3-NPA levels comparable to S. varia. 3-NPA could not be detected in the tested cosmetics containing A. vulneraria extracts.

CONCLUSIONS

Using highly sensitive analytical methods, new 3-NPA-containing species were identified. The developed validated quantitative method is suitable for the determination of 3-NPA concentrations in herbal samples.

Computational guided identification of potential leads from Acacia pennata (L.) Willd. as inhibitors for cellular entry and viral replication of SARS-CoV-2

BACKGROUND

Coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) started in 2019 and is still an on-going pandemic. SARS-CoV-2 uses a human protease called furin to aid in cellular entry and its main protease (M^pro) to achieve viral replication. By targeting these proteins, scientists are trying to identify phytoconstituents of medicinal plants as potential therapeutics for COVID-19. Therefore, our study was aimed to identify promising leads as potential inhibitors of SARS-CoV-2 M^pro and furin using the phytocompounds reported to be isolated from Acacia pennata (L.) Willd.

RESULTS

A total of 29 phytocompounds were reported to be isolated from A. pennata. Molecular docking simulation studies revealed 9 phytocompounds as having the top 5 binding affinities towards SARS-CoV-2 M^pro and furin. Among these phytocompounds, quercetin-3-O-α-L-rhamnopyranoside (C_18), kaempferol 3-O-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranoside (C_4), and isovitexin (C_5) have the highest drug score. However, C_18 and C_4 were not selected for further studies due to bioavailability issues and low synthetic accessibility. Based on binding affinity, molecular properties, drug-likeness, toxicity parameters, ligand interactions, bioavailability, synthetic accessibility, structure-activity relationship, and comparative analysis of our experimental findings with other studies, C_5 was identified as the most promising phytocompound. C_5 interacted with the active site residues of SARS-CoV-2 M^pro (GLU166, ARG188, GLN189) and furin (ASN295, ARG298, HIS364, THR365). Many phytocompounds that interacted with these amino acid residues were reported by other studies as potential inhibitors of SARS-CoV-2 M^pro and furin. The oxygen atom at position 18, the -OH group at position 19, and the 6-C-glucoside were identified as the pharmacophores in isovitexin (also known as apigenin-6-C-glucoside). Other in-silico studies reported apigenin as a potential inhibitor of SARS-CoV-2 M^pro and apigenin-o-7-glucuronide was reported to show stable conformation during MD simulations with SARS-CoV-2 M^pro.

CONCLUSION

The present study found isovitexin as the most promising phytocompound to potentially inhibit the cellular entry and viral replication of SARS-CoV-2. We also conclude that compounds having oxygen atom at position 18 (C-ring), -OH group at position 19 (A-ring), and 6-C-glucoside attached to the A-ring at position 3 on a C₆-C₃-C₆ flavonoid scaffold could offer the best alternative to develop new leads against SARS-CoV-2.

Isoorientin: A dietary flavone with the potential to ameliorate diverse metabolic complications

Isoorientin is a natural C-glucosyl flavone that is generating a lot of interest due to its multiple pharmacological activities. Increasing experimental data have shown that the robust antioxidant and anti-inflammatory properties of isoorientin remain important in ameliorating a number of metabolic complications. In fact, plants rich in isoorientin have demonstrated strong ameliorative properties against complications such as hyperglycemia, hyperlipidemia, and insulin resistance. However, while such evidence is accumulating, it has not been reviewed to better inform on the therapeutic potential of this flavone in improving human health. This review examines and extrapolates available literature on the potential beneficial or detrimental effects associated with the use of isoorientin in mitigating metabolic diseases, with a specific focus on diabetes, obesity, and insulin resistance, including associated complications. The discussion includes effective doses in various experimental settings and proposed molecular mechanisms by which isoorientin may exert its therapeutic effects. In addition, the protective effects of extracts of a number of isoorientin-rich plants against metabolic complications will be highlighted.

Computer-Aided 13C NMR Chemical Profiling of Crude Natural Extracts without Fractionation

A computer-aided, ¹³C NMR-based dereplication method is presented for the chemical profiling of natural extracts without any fractionation. An algorithm was developed in order to compare the ¹³C NMR chemical shifts obtained from a single routine spectrum with a set of predicted NMR data stored in a natural metabolite database. The algorithm evaluates the quality of the matching between experimental and predicted data by calculating a score function and returns the list of metabolites that are most likely to be present in the studied extract. The proof of principle of the method is demonstrated on a crude alkaloid extract obtained from the leaves of Peumus boldus, resulting in the identification of eight alkaloids, including isocorydine, rogersine, boldine, reticuline, coclaurine, laurotetanine, N-methylcoclaurine, and norisocorydine, as well as three monoterpenes, namely, p-cymene, eucalyptol, and α-terpinene. The results were compared to those obtained with other methods, either involving a fractionation step before the chemical profiling process or using mass spectrometry detection in the infusion mode or coupled to gas chromatography.

Computer-aided Dereplication and Structure Elucidation of Natural Products at the University of Reims

Natural product chemistry began in Reims, France, in a pharmacognosy research laboratory whose main emphasis was the isolation and identification of bioactive molecules, following the guidelines of chemotaxonomy. The structure elucidation of new compounds of steadily increasing complexity favored the emergence of methodological work in nuclear magnetic resonance. As a result, our group was the first to report the use of proton-detected heteronuclear chemical shift correlation spectra for the computer-assisted structure elucidation of small organic molecules driven by atom proximity relationships and without relying on databases. The early detection of known compounds appeared as a necessity in order to deal more efficiently with complex plant extracts. This goal was reached by an original combination of mixture fractionation by centrifugal partition chromatography, analysis by ¹³ C NMR, digital data reduction and alignment, hierarchical data clustering, and computer database search.