Flavonoid and Galloyl Glycosides Isolated from Saxifraga spinulosa and Their Antioxidative and Inhibitory Activities against Species That Cause Piroplasmosis

A review of the bioactive properties of Mongolian plants, with a focus on their potential as natural food preservatives

Consumers have recently preferred food that is easy to make and of excellent quality, as well as food that is safe, natural, and minimally processed, but has a longer shelf life. Food deteriorates over time as a result of microbiological, chemical, or physical changes. Phytochemicals derived from medicinal and food plants have long been recognized for their biological activity to protect plants. These bioactivities are designed to increase the shelf life of food while inhibiting the growth of microorganisms. The use of natural plant food preservatives containing bioactive compounds as health-promoting agents is particularly intriguing. Furthermore, due to their effectiveness against food spoilage and foodborne pathogens, natural plant-origin antimicrobial compounds have been investigated as alternatives to synthetic antimicrobial compounds for preserving food quality. This review focused on the plant composition and properties that can be utilized as a natural food preservative, as well as the possibilities of using Mongolian medicinal plants.

Perplexing Polyphenolics: The Isolations, Syntheses, Reappraisals, and Bioactivities of Flavonoids, Isoflavonoids, and Neoflavonoids from 2016 to 2022

Flavonoids, isoflavonoids, neoflavonoids, and their various subcategories are polyphenolics-an extensive class of natural products. These compounds are bioactive and display multiple activities, including anticancer, antibacterial, antiviral, antioxidant, and neuroprotective activities. Thus, these compounds can serve as leads for therapeutic agents or targets for complex synthesis; they are coveted and routinely isolated, characterized, biologically evaluated, and synthesized. However, data regarding the compounds' sources, isolation procedures, structural novelties, bioactivities, and synthetic schemes are often dispersed and complex, a dilemma this review aims to address. To serve as an easily accessible guide for researchers wanting to apprise themselves of the latest advancements in this subfield, this review summarizes seventy-six (76) articles published between 2016 and 2022 that detail the isolation and characterization of two hundred and forty-nine (249) novel compounds, the total and semisyntheses of thirteen (13) compounds, and reappraisals of the structures of twenty (20) previously reported compounds and their bioactivities. This article also discusses new synthetic methods and enzymes capable of producing or modifying flavonoids, isoflavonoids, or neoflavonoids.

Comparative Analysis of Chloroplast Genomes within Saxifraga (Saxifragaceae) Takes Insights into Their Genomic Evolution and Adaption to the High-Elevation Environment

Saxifraga species are widely distributed in alpine and arctic regions in the Northern hemisphere. Highly morphological diversity within this genus brings great difficulties for species identification, and their typical highland living properties make it interesting how they adapt to the extreme environment. Here, we newly generated the chloroplast (cp) genomes of two Saxifraga species and compared them with another five Saxifraga cp genomes to understand the characteristics of cp genomes and their potential roles in highland adaptation. The genome size, structure, gene content, GC content, and codon usage pattern were found to be highly similar. Cp genomes ranged from 146,549 bp to 151,066 bp in length, most of which comprised 130 predicted genes. Yet, due to the expansion of IR regions, the second copy of rps19 in Saxifraga stolonifera was uniquely kept. Through sequence divergence analysis, we identified seven hypervariable regions and detected some signatures of regularity associated with genetic distance. We also identified 52 to 89 SSRs and some long repeats among seven Saxifraga species. Both ML and BI phylogenetic analyses confirmed that seven Saxifraga species formed a monophyletic clade in the Saxifragaceae family, and their intragenus relationship was also well supported. Additionally, the ndhI and ycf1 genes were considered under positive selection in species inhabiting relatively high altitudes. Given the conditions of intense light and low CO₂ concentration in the highland, the products of these two genes might participate in the adaptation to the extreme environment.

Three new dihydroflavonols with free radical scavenging activity from Ribes himalense Royle ex Decne

Ribes himalense Royle ex Decne, a small shrub, is widely used as a Tibetan medicine in Chinese folk. In this study, three novel 1,1-diphenyl-2-picrylhydrazyl inhibitors named Rihimaside A, Rihimaside B, and Rihimaside C, as well as one known 1,1-diphenyl-2-picrylhydrazyl inhibitor, dihydromyricetin, were isolated from the leaves and stems of Ribes himalense Royle ex Decne using online high performance liquid chromatography-1,1-diphenyl-2-picrylhydrazyl activity screening system combined with medium and high-pressure liquid chromatography. All four 1,1-diphenyl-2-picrylhydrazyl inhibitors are dihydroflavonols. The 1,1-diphenyl-2-picrylhydrazyl scavenging activity and IC₅₀ values of three novel 1,1-diphenyl-2-picrylhydrazyl inhibitors were determined using 1,1-diphenyl-2-picrylhydrazyl methods. Rihimaside A, Rihimaside B, and Rihimaside C exhibited IC₅₀ values of 9.58 μg/mL, 12.57 μg/mL and 387 μg/mL, respectively.

In Vitro Potently Active Anti-Plasmodium and Anti-Toxoplasma Mongolian Plant Extracts

PURPOSE

Malaria and toxoplasmosis are important public health diseases affecting millions of people and animals each year, and there is a continuing need for new and improved treatments for them. Plants have provided many opportunities for new drug leads in pharmacology.

METHODS

We examined 43 crude extracts from Mongolian plants for their activities against the Plasmodium falciparum 3D7 strain and the Toxoplasma gondii RH strain using a SYBR Green-based fluorescence assay and a fluorescence-based assay, respectively. The potential toxicity of these extracts was also assessed on human foreskin fibroblast cells (HFF) using a cell viability assay.

RESULTS

From the initial screenings, 11 and 7 crude extracts were effective against T. gondii and P. falciparum, respectively, at 100 µg/ml concentration (≥ 80% inhibition activity). The 50% cytotoxic concentrations of the extracts were estimated on HFF cells, and their 50% inhibitory concentrations (IC₅₀s) were calculated. According to our lead criteria (selective index, SI; value ≥ 10), six plants (Galatella dahurica leaf + flower, Leonurus deminutus leaf + flower, Oxytropis trichophysa aerial part, Schultzia crinita whole plant, Leontopodium campestre root, Spirea salicifolia aerial part) inhibited P. falciparum growth at IC₅₀ values of 5.99-64.15 µg/ml (SI values: 10.11-17.02). Amaranthus retroflexus root was highly active against T. gondii (IC₅₀, 19.89 µg/ml; SI value, 38).

CONCLUSION

This first observation of the anti-Plasmodium and anti-Toxoplasma activities of Mongolian plant extracts shows them to be interesting potential candidates for drug discovery.

Preparative separation of 1,1-diphenyl-2-picrylhydrazyl inhibitors originating from Saxifraga sinomontana employing medium-pressure liquid chromatography in combination with reversed-phase liquid chromatography

Traditional Tibetan medicines elaborately document the health benefits of Saxifraga sinomontana. However, there have been limited reports on its chemical make-up, presumably because of the complicated separation and purification process. In this work, a methanolic extract of Saxifraga sinomontana was utilized for targeted separation of 4 key 1,1-diphenyl-2-picrylhydrazyl inhibitors employing the medium-pressure liquid chromatography, reversed-phase liquid chromatography in combination with on-line reversed-phase liquid chromatography-1,1-diphenyl-2-picrylhydrazyl detection. Pre-treatment of the sample was carried out by employing medium-pressure liquid chromatography using MCI GEL® CHP20P as the stationary phase, furnishing 2.4 g of fraction Fr3 and 3.4 g of fraction Fr4 (the percentage retrieval was 32.7%). The 1,1-diphenyl-2-picrylhydrazyl inhibitors contained in fractions Fr3 and Fr4 were subjected to additional separation using a C18 (ReproSil-Pur C18 AQ) column and yielded 106.2 mg of Fr3-1, 246.9 mg of Fr3-2, 248.5 mg of Fr4-1 and 41.8 mg of Fr4-2. The degree of purity, structures and 1,1-diphenyl-2-picrylhydrazyl inhibition activity of the isolated DPPH inhibitors were determined, and four 1,1-diphenyl-2-picrylhydrazyl inhibitors including two new diarylnonanoids (3-methoxy-4-hydroxyphenol-(6'-O-galloyl)-1-O-β-d-glucopyrano side with IC₅₀ of 39.6 μM, 3,4,5-trimethoxyphenyl-(6'-O-galloyl)-1-O-β-d-glucopyranoside with IC₅₀ of 46.9 μM, saximonsin A with IC₅₀ of 11.4 μM, and saximonsin B with IC₅₀ of 20.6 μM) were isolated with a percentage purity above 95%. The methodology thus evolved has good efficacy for preparatively isolating high-purity 1,1-diphenyl-2-picrylhydrazyl inhibitors from extracts of Saxifraga sinomontana and could be efficiently utilized for rapidly isolating 1,1-diphenyl-2-picrylhydrazyl inhibitors from other natural products.

Isolation and evaluation of virucidal activities of flavanone glycosides and rosmarinic acid derivatives from Dracocephalum spp. against feline calicivirus

Feline calicivirus is one of the surrogate viruses of human norovirus. This study aimed to identify virucidal compounds, chemical constituents of plants from the genus Dracocephalum, which are rich in flavonoids and phenylpropanoid oligomers. Four undescribed compounds, including a flavanone glucoside, two stilbenoid glycosides, and a phenylpropanoid amide glycoside, as well as 17 known compounds, were isolated from the Mongolian plants Dracocephalum fruticulosum Stephan ex Willd., and D. nutans L. belonging to the family Lamiaceae. The structures of the compounds were determined based on NMR, MS, and electronic CD spectroscopic data. In addition to these 21 compounds, 15 previously reported compounds from D. foetidum Bunge in C.F. von Ledebour were included, and a total of 36 compounds were evaluated for their virucidal activities against feline calicivirus. Some of the flavanone glycosides and phenylpropanoid oligomers showed virucidal activities, and their structural features are discussed. The findings suggest that isosakuranetin glycosides and phenylpropanoid oligomers may have the potential for norovirus inactivation.

Evaluation of Mongolian compound library for potential antimalarial and anti-Toxoplasma agents

179 compounds in a Mongolian compound library were investigated for their inhibitory effect on the in vitro growth of Plasmodium falciparum and Toxoplasma gondii. Among these compounds, brachangobinan A at a half-maximal inhibition concentration (IC₅₀) of 2.62 μM and a selectivity index (SI) of 27.91; 2-(2'-hydroxy-5'-O-methylphenyl)-5-(2″,5″-dihydroxyphenyl)oxazole (IC₅₀ 3.58 μM and SI 24.66); chrysosplenetin (IC₅₀ 3.78 μM and SI 15.26); 4,11-di-O-galloylbergenin (IC₅₀ 3.87 μM and SI 13.38); and 2-(2',5'-dihydroxyphenyl)-5-(2″-hydroxyphenyl)oxazole (IC₅₀ 6.94 μM and SI 11.48) were identified as potential inhibitors of P. falciparum multiplication. Additionally, tricin (IC₅₀ 12.94 μM and SI > 23.40) was identified as a potential inhibitor of T. gondii multiplication. Our findings represent a good starting point for developing novel antimalarial and anti-Toxoplasma therapeutics from Mongolian compounds.

Biological activity evaluations of chemical constituents derived from Mongolian medicinal forage plants and their applications in combating infectious diseases and addressing health problems in humans and livestock

Mongolian nomadic people possess traditional knowledge of wild plants that grow in their areas of habitation. Many of these are forage plants in nature and are consumed by livestock. However, these plants are known to have medicinal and/or toxic properties. To establish a scientific understanding of the plants, and in turn, offer sound knowledge on their applications and effective use, it is essential to collect data pertaining to the chemical constituents of each plant. Therefore, the first objective of this study was to identify and determine the structural constituents of the forage plants that were available to our research group. Furthermore, in an attempt to demonstrate the biological activities of the isolated chemical compounds, we focused on solving some of the social issues affecting Mongolian communities, including protozoan diseases affecting livestock, vectors of infectious diseases, and the general health of humans and their livestock. The results of the chemical constituents derived from Mongolian medicinal plants and their biological activities that were studied in the recent decade are also described herein.

Targeted isolation of 1,1-diphenyl-2-picrylhydrazyl inhibitors from Saxifraga atrata using medium- and high- pressure liquid chromatography combined with online high performance liquid chromatography-1,1-diphenyl-2- picrylhydrazyl detection

Traditional Tibetan medicine (TTM) is a valuable source of novel therapeutic lead molecules inspired by natural products (NPs). The health benefits of Saxifraga atrata are well documented in TTM, but reports on its chemical composition are limited, most likely due to the complicated purification process. Herein, target separation and identification of 4 main radical scavenging compounds from the methanolic extract of S. atrata was were performed using medium- and high-pressure liquid chromatography coupled with online HPLC-DPPH detection. The sample was pretreated using medium pressure liquid chromatography with MCI GELⓇ CHP20P styrene-divinylbenzene beads as a stationary phase, yielding 1.4 g of the target DPPH inhibitors (Fr4, 11.9% recovery). The compounds were further purified and isolated using HPLC on RP-C18 (ReproSil-Pur C18 AQ) followed by HILIC (Click XIon) column separation, resulting in 2.8 mg of fraction Fr4-1-1, 6.8 mg of fraction Fr4-2, 244.9 mg of the Fr4-3-1 sample, and 38.3 mg of Fr4-4-1. The structure and purity of the target compounds were determined, and four compounds (ethyl gallate, 11-O-galloylbergenin, rutin and isoquercitrin) were isolated with >95% purity. The developed methodology is efficient for targeted isolation of high-purity radical scavengers from NP extracts and could be used for rapid identification and isolation of DPPH inhibitors from various NPs.

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Equine piroplasmosis (EP), caused by the hemoparasites Theileria equi, Theileria haneyi, and Babesia caballi, is an important tick-borne disease of equines that is prevalent in most parts of the world. Infection may affect animal welfare and has economic impacts related to limitations in horse transport between endemic and non-endemic regions, reduced performance of sport horses and treatment costs. Here, we analyzed the epidemiological, serological, and molecular diagnostic data published in the last 20 years, and all DNA sequences submitted to GenBank database, to describe the current global prevalence of these parasites. We demonstrate that EP is endemic in most parts of the world, and that it is spreading into more temperate climates. We emphasize the importance of using DNA sequencing and genotyping to monitor the spread of parasites, and point to the necessity of further studies to improve genotypic characterization of newly recognized parasite species and strains, and their linkage to virulence.

Saxifraga spinulosa-Derived Components Rapidly Inactivate Multiple Viruses Including SARS-CoV-2

Novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza A virus (IAV), and norovirus (NV) are highly contagious pathogens that threaten human health. Here we focused on the antiviral potential of the medicinal herb, Saxifragaspinulosa (SS). Water-soluble extracts of SS were prepared, and their virus-inactivating activity was evaluated against the human virus pathogens SARS-CoV-2 and IAV; we also examined virucidal activity against feline calicivirus and murine norovirus, which are surrogates for human NV. Among our findings, we found that SS-derived gallocatechin gallate compounds were capable of inactivating all viruses tested. Interestingly, a pyrogallol-enriched fraction (Fr 1C) inactivated all viruses more rapidly and effectively than did any of the component compounds used alone. We found that 25 µg/mL of Fr 1C inactivated >99.6% of SARS-CoV-2 within 10 s (reduction of ≥2.33 log₁₀ TCID₅₀/mL). Fr 1C resulted in the disruption of viral genomes and proteins as determined by gel electrophoresis, electron microscopy, and reverse transcription–PCR. Taken together, our results reveal the potential of Fr 1C for development as a novel antiviral disinfectant.

Naphthylisoquinoline alkaloids and their synthetic analogs as potent novel inhibitors against Babesia canis in vitro

Babesia canis is the predominant and clinically relevant canine Babesia species in Europe. Transmitted by vector ticks, the parasite enters red blood cells and induces a severe, potentially fatal hemolytic anemia. Here, we report on the antibabesial activities of three extracts of the West African tropical plant species Triphyophyllum peltatum (Dioncophyllaceae) and Ancistrocladus abbreviatus (Ancistrocladaceae) and of 13 genuine naphthylisoquinoline alkaloids isolated thereof. Two of the extracts and eight of the alkaloids were found to display strong activities against Babesia canis in vitro. Among the most potent compounds were the C,C-coupled dioncophyllines A (1a) and C (2) and the N,C-linked alkaloids ancistrocladium A (3) and B (4), with half-maximum inhibition concentration (IC₅₀) values of 0.48 μM for 1a, 0.85 μM for 2, 1.90 μM for 3, and 1.23 μM for 4. Structure-activity relationship (SAR) studies on a small library of related genuine analogs and non-natural synthetic derivatives of 1a and 2 revealed the likewise naturally occurring alkaloid N-methyl-7-epi-dioncophylline A (6b) to be the most potent (IC₅₀, 0.14 μM) among the investigated compounds. Although none of the tested naphthylisoquinolines showed 100 % inhibition of parasite infection - as displayed by imidocarb dipropionate (IC₅₀, 0.07 μM), which was used as a positive control - the antibabesial potential of the dioncophyllines A (1a) and C (2) and related compounds such as 6b, its atropo-diastereomer 6a (IC₅₀, 1.45 μM), and 8-O-(p-nitrobenzyl)dioncophylline A (14) (IC₅₀, 0.82 μM) is to be considered as high. The SAR results showed that N-methylation and axial chirality exert a strong impact on the antibabasial activities of the naphthylisoquinolines presented here, whereas dimerization, as in jozimine A₂ (5) (IC₅₀, 140 μM), leads to a significant decrease of activity against B. canis. Alkaloids displaying good to high activities against B. canis like the dioncophyllines 1a, 2, 6a, and 6b were found to cause only a small degree of hemolysis (< 0.7 %), whereas compounds with moderate to weak antibabesial activities such as 6-O-methyl-4'-O-demethylancistrocladine (15a) (IC₅₀, 14.0 μM) and its atropo-diastereomer 6-O-methyl-4'-O-demethylhamatine (15b) (IC₅₀, 830 μM) caused a high degree of hemolysis (7.3 % for 15a and 11.2 % for 15b). In this respect, the most effective anti-Babesia naphthylisoquinolines are also the safest ones.

Preparative isolation of arylbutanoid-type phenol [(-)-rhododendrin] with peak tailing on conventional C18 column using middle chromatogram isolated gel column coupled with reversed-phase liquid chromatography

Reversed-phase liquid chromatography coupled with middle chromatogram isolated gel column was employed for the efficient preparative separation of the arylbutanoid-type phenol [(-)-rhododendrin] from Saxifraga tangutica. Universal C18 (XTerra C18) and XCharge C18 columns were compared for (-)-rhododendrin fraction analysis and preparation. Although tailing and overloading occurred on the XTerra C18 column, the positively charged reversed-phase C18 column (XCharge C18) overcame these drawbacks, allowing for favorable separation resolution, even when loading at a on a preparative scale (3.69 mg per injection). The general separation process was as follows. First, 365.0 mg of crude (-)-rhododendrin was enriched from 165 g Saxifraga tangutica extract via a middle chromatogram isolated gel column. Second, separation was performed on an XTerra C18 preparative column, from which 73.8 mg of the target fraction was easily obtained. Finally, the 24.0 mg tailing peak of (-)-rhododendrin on XTerra C18 column was selectively purified on the XCharge C18 analytical column. These results demonstrate that the tailing nonalkaloid peaks can be effectively used for preparative isolation on XCharge C18 columns.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Palhinosides A-H: Flavone Glucosidic Truxinate Esters with Neuroprotective Activities from Palhinhaea cernua

Palhinosides A-H (1-8), new flavone glucosidic truxinate esters, including β-truxinate and μ-truxinate forms, were isolated from Palhinhaea cernua. Their structures were elucidated by extensive spectroscopic methods and chemical analyses. The flavone glucoside cyclodimers possess a unique cyclobutane ring in their carbon scaffolds. Compounds 2-7 represent three pairs of stereoisomers (2/3, 4/5, 6/7). The protective effects of 1-8 against the damage of HT-22 cells induced by l-glutamate were evaluated, and compounds 4 and 5 showed better neuroprotective effects than the positive control, Trolox.

Two novel flavonoids from the leaves of Rhododendron dauricum L. with their inhibition of TNF-α production in LPS-induced RAW 264.7 cells

Two new flavonoids, (2S)-6,8-dimethyl-5,7,3',4'-tetrahydroxyflavanone 4'-O-β-D-glucopyranoside (1) and quercetin 3-O-β-D-(6''-p-methoxybenzoyl)-galactopyranoside (2), together with ten known flavonoids (3-12) were isolated from the leaves of Rhododendron dauricum L. The structures of the flavonoids were characterized from spectroscopic data (1D and 2D NMR and HR-ESI-MS). The isolated flavonoids were evaluated for their inhibitory effects on the production of tumour necrosis factor (TNF)-α in LPS-stimulated RAW 264.7 cells. Compound 11 exhibited inhibitory activity against TNF-α production with an IC₅₀ value of 46.2 ± 1.2 µM.

Flavonoids isolated from the flowers of Pulsatilla flavescens and their anti-piroplasm activity

Pulsatilla species are known as "Yargui", and their flowers are traditionally used in Mongolia as a tonic and for the treatment of inflammatory diseases. By chemical investigation of P. flavescens flowers, 21 flavonoids, including a new chalcone C-glucoside, chalconaringenin 2'-O-β-D-glucopyranosyl-5'-β-D-glucopyranoside, and two new flavanone C-glucosides, (2R)- and (2S)-naringenin 8-β-D-glucopyranosyl-4'-O-β-D-glucopyranoside, were isolated. The absolute configurations of the seven flavanone glucosides were elucidated by ECD spectra. For the isolated compounds, inhibitory activity against Babesia caballi and Theileria equi, which cause fatal diseases in horses, was estimated. Although most of the isolated chalcone and flavanone derivatives did not show any anti-piroplasm activity, all the isolated flavone and flavonol derivatives showed moderate effects against B. caballi and/or T. equi.

Survey of natural products reported by Asian research groups in 2017

The new natural products reported in 2017 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2017 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.