New antibacterial dihydrochalcone derivatives from buds of Populus balsamifera

Organic extracts from sustainable hybrid poplar hairy root cultures as potential natural antimicrobial and antibiofilm agents

In order to meet growing consumer demands in terms of naturalness, the pharmaceutical, food, and cosmetic industries are looking for active molecules of plant origin. In this context, hairy roots are considered a promising biotechnological system for the sustainable production of compounds of interest. Poplars (genus Populus, family Salicaceae) are trees of ecological interest in temperate alluvial forests and are also cultivated for their industrial timber. Poplar trees also produce specialized metabolites with a wide range of bioactive properties. The present study aimed to assess the hybrid poplar hairy root extracts for antimicrobial and antibiofilm activities against four main life-threatening strains of Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. Ethyl acetate extracts from two hairy root lines (HP15-3 and HP A4-12) showed significant antibacterial properties as confirmed by disc diffusion assay. Antibiofilm activities were found to be dose dependent with significant biofilm inhibition (75-95%) recorded at 1000 µg.mL-1 in all the bacterial strains tested. Dose-dependent enhancement in the release of exopolysaccharides was observed in response to treatment with extracts, possibly because of stress and bacterial cell death. Fluorescence microscopy confirmed loss of cell viability of treated bacterial cells concomitant with increased production of reactive oxygen species compared to the untreated control. Overall, this study demonstrates for the first time a high potential of poplar hairy root extracts as a natural and safe platform to produce antimicrobial agents in pharmaceutical, food, industrial water management, or cosmetic industries.

Antiproliferative and Anti-Inflammatory Effects of the Polyphenols Phloretin and Balsacone C in a Coculture of T Cells and Psoriatic Keratinocytes

Plaque psoriasis is a chronic inflammatory skin disease causing red inflamed lesions covered by scales. Leukocytes, including dendritic cells and T cells, participate in the inflammation of the skin by producing multiple cytokines, thus contributing to the hyperproliferation of keratinocytes. Lack of effectiveness and toxic side effects are the main concerns with conventional treatments, and research involving new antipsoriatic molecules is essential. In this study, the anti-inflammatory and antiproliferative effects of two natural polyphenols, phloretin and balsacone C, were investigated using the coculture of T cells and psoriatic keratinocytes. Phloretin exerted antiproliferative activity by regulating the expression of antigen Ki67 and proliferating cell nuclear antigen (PCNA). These effects were comparable to those of methotrexate, a reference treatment for moderate to severe psoriasis. With balsacone C, the expression of Ki67 was also reduced. Additionally, phloretin decreased the levels of multiple pro-inflammatory cytokines: monocyte chemoattractant protein-1 (MCP-1/CCL2), macrophage inflammatory protein-1α (MIP-1α), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-1 alpha (IL-1α), interleukin-1 beta (IL-1β), interleukin-6 (IL-6), interleukin-17A (IL-17A), and tumor necrosis factor alpha (TNF-α). The increased interleukin-2 (IL-2) levels with phloretin and methotrexate also represented anti-inflammatory activity. Balsacone C and methotrexate decreased the levels of IL-1α and IL-1β, but methotrexate exerted a higher reduction. In summary, the anti-inflammatory effects of phloretin were more pronounced than those of methotrexate and balsacone C. In addition, the expression of lymphocyte common antigen (CD45) was more similar to that of the healthy condition after using phloretin or methotrexate. Finally, phloretin stood out from the other compounds and appears promising for psoriasis treatment.

Characterization of Secondary Metabolites of Leaf Buds from Some Species and Hybrids of Populus by Gas Chromatography Coupled with Mass Detection and Two-Dimensional High-Performance Thin-Layer Chromatography Methods with Assessment of Their Antioxidant Activity

Poplars provide medicinal raw plant materials used in pharmacy. Leaf buds are one of the herbal medicinal products collected from poplars, having anti-inflammatory and antiseptic properties, but there are no quality standards for their production and there is a need to determine their botanical sources. Therefore, the chemical compositions of the leaf buds from four species and varieties of poplars, Populus balsamifera, P. × berolinensis, P. × canadensis 'Marilandica', and P. wilsonii were investigated and compared using gas chromatography coupled with mass detection (GC-MS) and two-dimensional high-performance thin-layer chromatography (2D-HPTLC) in order to search for taxa characterized by a high content of biologically active compounds and with a diverse chemical composition that determines their therapeutic effects. The presence of 163 compounds belonging to the groups of flavonoids, phenolic acids derivatives, glycerides, and sesquiterpenes was revealed. Moreover, the conditions for the separation and identification of biologically active compounds occurring in analyzed leaf buds using 2D-HPTLC were optimized and used for metabolomic profiling of the studied poplars, enabling their fast and simple botanical identification. The total phenolic (TPC) and flavonoid (TFC) contents of examined extracts were determined and their antioxidant capacities were estimated by spectrophotometric DPPH, ABTS, and FRAP assays. Based on the analysis of phytochemicals and antioxidant activity, P. × berolinensis buds were selected as the raw plant material for medicinal purposes with the highest content of active compounds and the strongest antioxidant activity.

Synthesis of Asebogenin and Balsacone A Precursor by a Novel Synthetic Strategy: Recent Opportunities for and Challenges of Total Synthesis of Balsacone A

One of the main areas of interest of synthetic organic chemistry is the rapid construction of small molecules with proven diverse biological activities for the development of new strategies to cure human health. In particular, the development of novel synthetic strategies is the most important option for reaching the molecular scaffolds of active molecules of natural origin. Balsacone A and asebogenin are compounds that exhibit a wide variety of important biological activities. In this respect, it has become very important to develop new strategies for the construction of biologically active natural and synthetic balsacone analogues. In particular, balsacone derivatives with hydroxy-substituted dihydrochalcone skeletons can be isolated from plant sources or obtained by hemi-syntheses using bio-sourced precursors. An efficient synthetic strategy to synthetically obtain balsacone A is the aim of the present study that considers the limited natural availability of these molecules as well as other factors, such as cost and time. Starting with phloroglucinol, a nine-step synthesis of the precursor of balsacone A was achieved at a 10% overall yield. Furthermore, asebogenin, which has a dihydrochalcone structure and plays a key role in the synthesis of balsacone A, was synthesised with a good yield.

Hemisynthesis and Biological Evaluation of Cinnamylated, Benzylated, and Prenylated Dihydrochalcones from a Common Bio-Sourced Precursor

Several families of naturally occurring C-alkylated dihydrochalcones display a broad range of biological activities, including antimicrobial and cytotoxic properties, depending on their alkylation sidechain. The catalytic Friedel-Crafts alkylation of the readily available aglycon moiety of neohesperidin dihydrochalcone was performed using cinnamyl, benzyl, and isoprenyl alcohols. This procedure provided a straightforward access to a series of derivatives that were structurally related to natural balsacones, uvaretin, and erioschalcones, respectively. The antibacterial and cytotoxic potential of these novel analogs was evaluated in vitro and highlighted some relations between the structure and the pharmacological properties of alkylated dihydrochalcones.

Plant synthetic biology for producing potent phyto-antimicrobials to combat antimicrobial resistance

Inappropriate and injudicious use of antimicrobial drugs in human health, hygiene, agriculture, animal husbandry and food industries has contributed significantly to rapid emergence and persistence of antimicrobial resistance (AMR), one of the serious global public health threats. The crisis of AMR versus slower discovery of newer antibiotics put forth a daunting task to control these drug-resistant superbugs. Several phyto-antimicrobials have been identified in recent years with direct-killing (bactericidal) and/or drug-resistance reversal (re-sensitization of AMR phenotypes) potencies. Phyto-antimicrobials may hold the key in combating AMR owing to their abilities to target major microbial drug-resistance determinants including cell membrane, drug-efflux pumps, cell communication and biofilms. However, limited distribution, low intracellular concentrations, eco-geographical variations, beside other considerations like dynamic environments, climate change and over-exploitation of plant-resources are major blockades in full potential exploration phyto-antimicrobials. Synthetic biology (SynBio) strategies integrating metabolic engineering, RNA-interference, genome editing/engineering and/or systems biology approaches using plant chassis (as engineerable platforms) offer prospective tools for production of phyto-antimicrobials. With expanding SynBio toolkit, successful attempts towards introduction of entire gene cluster, reconstituting the metabolic pathway or transferring an entire metabolic (or synthetic) pathway into heterologous plant systems highlight the potential of this field. Through this perspective review, we are presenting herein the current situation and options for addressing AMR, emphasizing on the significance of phyto-antimicrobials in this apparently post-antibiotic era, and effective use of plant chassis for phyto-antimicrobial production at industrial scales along with major SynBio tools and useful databases. Current knowledge, recent success stories, associated challenges and prospects of translational success are also discussed.

Rapid identification model based on decision tree algorithm coupling with 1H NMR and feature analysis by UHPLC-QTOFMS spectrometry for sandalwood

Sandalwood is one of the most valuable woods in the world. However, today's counterfeits are widespread, it is difficult to distinguish authenticity. In this paper, similar genus (Dalbergia and Pterocarpus) and confused species (Gluta sp.) of sandalwood were quickly and efficiently identified. Rapid identification model based on ¹H NMR and decision tree (DT) algorithm was firstly developed for the identification of sandalwood, and the accuracy was improved by introducing the AdaBoost algorithm. The accuracy of the final model was above 95%. And the feature components between different species of sandalwood were further explored using UHPLC-QTOFMS and NMR spectrometry. The results showed that 183 compounds were identified, among which 99 were known components, 84 were unknown components. The ¹H NMR and ¹³C NMR signals of 505 samples were assigned, among them, 14 compounds were attributed, characteristic chemical shift intervals with great differences in the model were analysed. Furthermore, the fragmentation pattern of different compounds from sandalwood, in both positive and negative ion ESI modes, was summarized. The results showed a potential and rapid tool based on DT, NMR spectroscopy and UHPLC-QTOFMS, which had performed great potential for rapid identification and feature analysis of sandalwood.

A novel chresdihydrochalcone from Streptomyces chrestomyceticus exhibiting activity against Gram-positive bacteria

Microbial-derived natural products provide unique bioactivities and serve as a unique source of drug leads. In the present study, we isolated one new chresdihydrochalcone (1), one new chresphenylacetone (2), and one known streptimidone (3) from Streptomyces chrestomyceticus BCC 24770 using antibacterial activity-guided isolation and purification procedures. We determined their molecular weights using MS and HRMS and elucidated their chemical structures from their 1D and 2D NMR and electronic circular dichroism (ECD) spectra. Compound 1 showed moderate inhibitory activities against the Gram-positive bacteria Methicillin-resistant Staphylococcus aureus, Bacillus subtilis, and Micrococcus luteus. Cytotoxicity and hemolytic activity were not observed at a concentration of up to 100 μg ml^-1. The specific antimicrobial activity and low toxicity of compound 1 indicate this compound to be a potential antibiotic candidate, especially as antibiotic resistance has become a significant public health threat.

Dihydrochalcone Derivatives from Populus balsamifera L. Buds for the Treatment of Psoriasis

Psoriasis is a skin disorder characterized by epidermal hyperplasia, hyperkeratosis, and inflammation. The treatments currently available on the market only improve patients' quality of life and are associated with undesirable side effects. Thus, research leading to the development of new, effective, and safer therapeutic agents is still relevant. Populus balsamifera L. buds were used traditionally by Native Americans to treat various skin pathologies such as eczema and psoriasis. In this study, the antipsoriatic activities of dihydrochalcone derivatives from Populus balsamifera L. buds, known as balsacones, were investigated. The experiments were performed in vitro using a psoriatic skin substitute model. Also, anti-inflammatory and antioxidant activities were investigated. The tested balsacones showed promising antipsoriatic properties by slowing down cell growth and by regulating the expression of involucrin, loricrin, and Ki67 better than methotrexate in psoriatic substitutes. All five tested compounds could be an effective topical treatment for psoriasis, with promising anti-inflammatory and antioxidant actions that may contribute to clinical improvement in patients with psoriasis.

Dihydrochalcones: Methods of Acquisition and Pharmacological Properties-A First Systematic Review

Dihydrochalcones are a class of secondary metabolites, for which demand in biological and pharmacological applications is still growing. They posses several health-endorsing properties and, therefore, are promising candidates for further research and development. However, low content of dihydrochalcones in plants along with their low solubility and bioavailability restrict the development of these compounds as clinical therapeutics. Therefore, chemomicrobial and enzymatic modifications are required to expand their application. This review aims at analyzing and summarizing the methods of obtaining dihydrochalcones and of presenting their pharmacological actions that have been described in the literature to support potential future development of this group of compounds as novel therapeutic drugs. We have also performed an evaluation of the available literature on beneficial effects of dihydrochalcones with potent antioxidant activity and multifactorial pharmacological effects, including antidiabetic, antitumor, lipometabolism regulating, antioxidant, anti-inflammatory, antibacterial, antiviral, and immunomodulatory ones. In addition, we provide useful information on their properties, sources, and usefulness in medicinal chemistry.

New composites based on starch/Ecoflex®/biomass wastes: Mechanical, thermal, morphological and antimicrobial properties

Different biomass wastes were successfully blended with starch and Ecoflex® viz. poly(butylene adipate-co-terephthalate), without glycerol addition, to obtain biocomposite materials. The mechanical properties, as well as thermal and surface properties, of the developed composites were evaluated. It was found that the tensile strength and impact strength improved upon the addition of lignin, while the water uptake capacity decreased. The presence of 5% lignin determined an increase in tensile strength of 125.4% for materials comprising celery (CEL), 109.6% for materials comprising poplar seed hair fibers (PSH), 92.9% for materials comprising pomace (POM) and 127.7% for materials comprising Asclepias syriaca fibers (ASF), compared with a reference sample. The addition of lignin to all the formulations conferred good antimicrobial properties against different microorganisms, S. aureus and especially E. coli. The good mechanical properties, water resistance and antimicrobial activity against pathogens recommend these composites to be used in the manufacture of packaging materials.

Antibacterial Activity of Chalcone and Dihydrochalcone Compounds from Uvaria chamae Roots against Multidrug-Resistant Bacteria

This study presents antimicrobial properties of Uvaria chamae roots, commonly used for the treatment of various infections in south Benin. Their constituents were extracted and then fractionated in order to isolate the active ingredients. Antimicrobial susceptibility tests were performed against several multidrug-resistant bacteria using the Mueller Hilton well agar diffusion method. Results showed that ethanol extracts were highly active against Gram-positive cocci. This activity was more extensive than that measured from conventional broad-spectrum antibiotics. Indeed, vancomycin-resistant enterococcus (VRE) and methicillin-resistant Staphylococcus aureus (MRSA) strains were all sensitive to this root extract. The aim of this study was to link the antimicrobial activity of the root to chemical structures. The ion mobility mass spectrometry analysis revealed for the first time the presence of ten chalcone and dihydrochalcone structures responsible for the antimicrobial activity of Uvaria chamae ethanol extracts. Two structures were described here for the first time in these roots. These findings confirm and justify the medical properties of these roots used as a traditional medicine.

Cytotoxic cardenolides and sesquiterpenoids from the fruits of Reevesia formosana

Bioassay-guided fractionation of the fruits of Reevesia formosana led to isolation of three cardenolides (reevesioside J, reevesioside K, and epi-reevesioside K), three sesquiterpenoids (reevesiterpenol C, reevesiterpenol D, and reevesiterpenol E), and two glycosides (reevesianin A and reevesianin B), along with 46 known compounds. Their structures were determined using spectroscopic techniques. In addition to the reported cytotoxic cardenolides, reevesioside J and strophanthidin exhibited moderate cytotoxicity against the cell lines MCF-7, NCI-H460, and HepG2, with IC50 values of 0.39 ± 0.06 μM and 1.06 ± 0.12 μM for MCF-7, 0.12 ± 0.01 μM and 0.29 ± 0.01 μM for NCI-H460, and 1.09 ± 0.02 μM and 1.72 ± 0.02 μM for HepG2, respectively. Reevesiterpenol E also exhibited the best selective cytotoxicity to the NCI-H460 cell line, with an IC50 value of 3.15 ± 0.22 μM.

The Search for Herbal Antibiotics: An In-Silico Investigation of Antibacterial Phytochemicals

Recently, the emergence and spread of pathogenic bacterial resistance to many antibiotics (multidrug-resistant strains) have been increasing throughout the world. This phenomenon is of great concern and there is a need to find alternative chemotherapeutic agents to combat these antibiotic-resistant microorganisms. Higher plants may serve as a resource for new antimicrobials to replace or augment current therapeutic options. In this work, we have carried out a molecular docking study of a total of 561 antibacterial phytochemicals listed in the Dictionary of Natural Products, including 77 alkaloids (17 indole alkaloids, 27 isoquinoline alkaloids, 4 steroidal alkaloids, and 28 miscellaneous alkaloids), 99 terpenoids (5 monoterpenoids, 31 sesquiterpenoids, 52 diterpenoids, and 11 triterpenoids), 309 polyphenolics (87 flavonoids, 25 chalcones, 41 isoflavonoids, 5 neoflavonoids, 12 pterocarpans, 10 chromones, 7 condensed tannins, 11 coumarins, 30 stilbenoids, 2 lignans, 5 phenylpropanoids, 13 xanthones, 5 hydrolyzable tannins, and 56 miscellaneous phenolics), 30 quinones, and 46 miscellaneous phytochemicals, with six bacterial protein targets (peptide deformylase, DNA gyrase/topoisomerase IV, UDP-galactose mutase, protein tyrosine phosphatase, cytochrome P450 CYP121, and NAD⁺-dependent DNA ligase). In addition, 35 known inhibitors were docked with their respective targets for comparison purposes. Prenylated polyphenolics showed the best docking profiles, while terpenoids had the poorest. The most susceptible protein targets were peptide deformylases and NAD⁺-dependent DNA ligases.

In-silico screening for anti-Zika virus phytochemicals

Zika virus (ZIKV) is an arbovirus that has infected hundreds of thousands of people and is a rapidly expanding epidemic across Central and South America. ZIKV infection has caused serious, albeit rare, complications including Guillain-Barré syndrome and congenital microcephaly. There are currently no vaccines or antiviral agents to treat or prevent ZIKV infection, but there are several ZIKV non-structural proteins that may serve as promising antiviral drug targets. In this work, we have carried out an in-silico search for potential anti-Zika viral agents from natural sources. We have generated ZIKV protease, methyltransferase, and RNA-dependent RNA polymerase using homology modeling techniques and we have carried out molecular docking analyses of our in-house virtual library of phytochemicals with these protein targets as well as with ZIKV helicase. Overall, 2263 plant-derived secondary metabolites have been docked. Of these, 43 compounds that have drug-like properties have exhibited remarkable docking profiles to one or more of the ZIKV protein targets, and several of these are found in relatively common herbal medicines, suggesting promise for natural and inexpensive antiviral therapy for this emerging tropical disease.

Structure elucidation of anti-methicillin resistant Staphylococcus aureus (MRSA) flavonoids from balsam poplar buds

There is nowadays an urgent need for developing novel generations of antibiotic agents due to the increased resistance of pathogenic bacteria. As a rich reservoir of structurally diverse compounds, plant species hold promise in this regard. Within this framework, we isolated a unique series of antibacterial flavonoids, named balsacones N-U, featuring multiple cinnamyl chains on the flavan skeleton. The structures of these compounds, isolated as racemates, were determined using extensive 1D and 2D NMR analysis in tandem with HRMS. Balsacones N-U along with previously isolated balsacones A-M were evaluated for their antibacterial activity against clinical isolates of methicillin resistant Staphylococcus aureus (MRSA). Several of the tested balsacones were potent anti-MRSA agents showing MIC values in the low micromolar range. Structure-activity relationships study highlighted some important parameters involved in the antibacterial activity of balsacones such as the presence of cinnamyl and cinnamoyl chains at the C-3 and C-8 positions of the flavan skeleton, respectively. These results suggest that balsacones could represent a potential novel class of naturally occurring anti-MRSA agents.

Precursor-Directed Combinatorial Biosynthesis of Cinnamoyl, Dihydrocinnamoyl, and Benzoyl Anthranilates in Saccharomyces cerevisiae

Biological synthesis of pharmaceuticals and biochemicals offers an environmentally friendly alternative to conventional chemical synthesis. These alternative methods require the design of metabolic pathways and the identification of enzymes exhibiting adequate activities. Cinnamoyl, dihydrocinnamoyl, and benzoyl anthranilates are natural metabolites which possess beneficial activities for human health, and the search is expanding for novel derivatives that might have enhanced biological activity. For example, biosynthesis in Dianthus caryophyllus is catalyzed by hydroxycinnamoyl/benzoyl-CoA:anthranilate N-hydroxycinnamoyl/ benzoyltransferase (HCBT), which couples hydroxycinnamoyl-CoAs and benzoyl-CoAs to anthranilate. We recently demonstrated the potential of using yeast (Saccharomyces cerevisiae) for the biological production of a few cinnamoyl anthranilates by heterologous co-expression of 4-coumaroyl:CoA ligase from Arabidopsis thaliana (4CL5) and HCBT. Here we report that, by exploiting the substrate flexibility of both 4CL5 and HCBT, we achieved rapid biosynthesis of more than 160 cinnamoyl, dihydrocinnamoyl, and benzoyl anthranilates in yeast upon feeding with both natural and non-natural cinnamates, dihydrocinnamates, benzoates, and anthranilates. Our results demonstrate the use of enzyme promiscuity in biological synthesis to achieve high chemical diversity within a defined class of molecules. This work also points to the potential for the combinatorial biosynthesis of diverse and valuable cinnamoylated, dihydrocinnamoylated, and benzoylated products by using the versatile biological enzyme 4CL5 along with characterized cinnamoyl-CoA- and benzoyl-CoA-utilizing transferases.

Antibacterial Balsacones J-M, Hydroxycinnamoylated Dihydrochalcones from Populus balsamifera Buds

A phytochemical investigation of buds from the hardwood tree Populus balsamifera led to the isolation of six new cinnamoylated dihydrochalcones as pairs of racemates and one as a racemic mixture along with the known compound iryantherin-D (2), the absolute configuration of which was determined for the first time. The structures of balsacones J (1), K (3), L (4), and M (5) were elucidated on the basis of spectroscopic data (1D and 2D NMR, IR, and MS). Chiral HPLC separations were carried out, and the absolute configuration of the isolated enantiomers unambiguously established via X-ray diffraction analyses and electron circular dichroism spectroscopic data. Each of the purified enantiomers exhibited potent in vitro antibacterial activity against Staphylococcus aureus with IC50 values ranging from 0.61 to 6 μM.

Balsacones D-I, dihydrocinnamoyl flavans from Populus balsamifera buds

A phytochemical investigation of an ethanolic extract from Populus balsamifera L. buds resulted in the isolation and characterization of twelve new flavan derivatives consisting of six pairs of enantiomers. Structures of (+) and (-)-balsacones D-I were elucidated based on spectroscopic data (1D and 2D NMR, MS) and their absolute configurations were established using X-ray single crystal diffraction analysis and ECD computational calculations. Antibacterial activity and cytotoxicity of all purified enantiomers were evaluated in vitro against Staphylococcus aureus and human skin fibroblast cells, respectively.