Bioactivity-Guided Metabolite Profiling of Feijoa ( Acca sellowiana) Cultivars Identifies 4-Cyclopentene-1,3-dione as a Potent Antifungal Inhibitor of Chitin Synthesis

Design, synthesis, antifungal evaluation and mechanism study of novel norbornene derivatives as potential laccase inhibitors

BACKGROUND

To discover novel fungicide candidates, five series of novel norbornene hydrazide, bishydrazide, oxadiazole, carboxamide and acylthiourea derivatives (2a-2t, 3a-3f, 4a-4f, 5a-5f and 7a-7f) were designed, synthesized and assayed for their antifungal activity toward seven representative plant fungal pathogens.

RESULTS

In the in vitro antifungal assay, some title norbornene derivatives presented good antifungal activity against Botryosphaeria dothidea, Sclerotinia sclerotiorum and Fusarium graminearum. Especially, compound 2b exhibited the best inhibitory activity toward B. dothidea with the median effective concentration (EC50) of 0.17 mg L-1, substantially stronger than those of the reference fungicides boscalid and carbendazim. The in vivo antifungal assay on apples revealed that 2b had significant curative and protective effects, both of which were superior to boscalid. In the preliminary antifungal mechanism study, 2b was able to injure the surface morphology of hyphae, destroy the cell membrane integrity and increase the intracellular reactive oxygen species (ROS) level of B. dothidea. In addition, 2b could considerably inhibit the laccase activity with the median inhibitory concentration (IC50) of 1.02 μM, much stronger than that of positive control cysteine (IC50 = 35.50 μM). The binding affinity and interaction mode of 2b with laccase were also confirmed by molecular docking.

CONCLUSION

This study presented a promising lead compound for the study of novel laccase inhibitors as fungicidal agrochemicals, which demonstrate significant anti-B. dothidea activity and laccase inhibitory activity. © 2024 Society of Chemical Industry.

Chemical genomic analysis reveals the interplay between iron chelation, zinc homeostasis, and retromer function in the bioactivity of an ethanol adduct of the feijoa fruit-derived ellagitannin vescalagin

Nature has been a rich source of pharmaceutical compounds, producing 80% of our currently prescribed drugs. The feijoa plant, Acca sellowiana, is classified in the family Myrtaceae, native to South America, and currently grown worldwide to produce feijoa fruit. Feijoa is a rich source of bioactive compounds with anticancer, anti-inflammatory, antibacterial, and antifungal activities; however, the mechanism of action of these compounds is largely not known. Here, we used chemical genetic analyses in the model organism Saccharomyces cerevisiae to investigate the mechanism of action of a feijoa-derived ethanol adduct of vescalagin (EtOH-vescalagin). Genome-wide barcode sequencing analysis revealed yeast strains lacking genes in iron metabolism, zinc metabolism, retromer function, or mitochondrial function were hypersensitive to 0.3 µM EtOH-vescalagin. This treatment increased expression of iron uptake proteins at the plasma membrane, which was a compensatory response to reduced intracellular iron. Likewise, EtOH-vescalagin increased expression of the Cot1 protein in the vacuolar membrane that transports zinc into the vacuole to prevent cytoplasmic accumulation of zinc. Each individual subunit in the retromer complex was required for the iron homeostatic mechanism of EtOH-vescalagin, while only the cargo recognition component in the retromer complex was required for the zinc homeostatic mechanism. Overexpression of either retromer subunits or high-affinity iron transporters suppressed EtOH-vescalagin bioactivity in a zinc-replete condition, while overexpression of only retromer subunits increased EtOH-vescalagin bioactivity in a zinc-deficient condition. Together, these results indicate that EtOH-vescalagin bioactivity begins with extracellular iron chelation and proceeds with intracellular transport of zinc via the retromer complex. More broadly, this is the first report of a bioactive compound to further characterize the poorly understood interaction between zinc metabolism and retromer function.

Phytochemical profiling and antioxidant evaluation of Rhododendron arboreum Sm leaf and flower: integrative analysis using advanced analytical techniques

OBJECTIVE

This study investigates the biological activities of Rhododendron arboreum Sm from the eastern Himalayas, addressing a literature gap on its properties. It explores the plant's phytochemical, antioxidant, and medicinal characteristics.

SIGNIFICANCE

Evaluating methanolic extracts of R. arboreum offers valuable insights into its bioactive potential. Comprehensive GC-MS analysis identified a diverse array of compounds, highlighting the plant's chemical composition.

METHODS

Methanolic leaf and flower extracts underwent sequential extraction and phytochemical profiling using column chromatography, TLC, and GC-MS analysis. Spectral studies aided compound identification, and antioxidant activity was assessed via spectrophotometric assays.

RESULTS

Column chromatography separated methanol leaf and flower extracts into 17 and 24 distinct fractions, respectively. TLC analysis showed specific Rf values for leaf (0.58, 0.65, 0.75, 0.8, 0.86, 0.9) and flower samples (0.91, 0.38, 0.48, 0.51, 0.56, 0.6, 0.65, 0.75, 0.85, 0.96). GC-MS analysis revealed a variety of organic functional groups, including aliphatic hydrocarbons, aromatic compounds, heterocyclic molecules, phenolic compounds, steroids, terpenoids, alcohols, esters, and other bioactive compounds. FTIR spectra identified functional groups such as hydroxyls, primary amines, alkanes, and alkynes. NMR data indicated a complex molecular composition with diverse proton environments. Leaf extracts demonstrated superior antioxidant activity compared to flower extracts in DPPH, ABTS, hydrogen peroxide scavenging, lipid peroxidation inhibition, and FRAP assays.

CONCLUSION

The study identifies diverse phytochemicals in R.arboreum extracts and highlights their potential applications in pharmaceuticals, nutraceuticals, and functional foods, owing to the superior antioxidant activity of leaf extracts compared to flowers.

A Review of the Ethnobotanical Use, Chemistry and Pharmacological Activities of Constituents Derived from the Plant Genus Geijera (Rutaceae)

Geijera Schott is a plant genus of the Rutaceae Juss. (rue and citrus) family, comprising six species which are all native to Oceania. Of the plants belonging to this genus, the most significant species that has a customary use is Geijera parviflora, which was used by Indigenous Australians, primarily as a pain reliever. Herein, a comprehensive review of the literature published on the genus Geijera from 1930 to 2023 was conducted. This is the first review for this plant genus, and it highlights the chemical constituents reported to date, together with the range of pharmacological properties described from the various species and different parts of the plant. These properties include anti-inflammatory, anti-microbial, anti-parasitic, insect repellent, analgesic, neuroactive, and anti-cancer activities. Finally, a reflection on some of the important areas for future focused studies of this plant genus is provided.

Establishment of feijoa (Acca sellowiana) callus and cell suspension cultures and identification of arctigenin - a high value bioactive compound

Feijoa (Acca sellowiana (O. Berg.) Burret), also known as pineapple guava, is a member of the Myrtaceae family and is well known for its fruit. Chemical profiling of the different tissues of the feijoa plant has shown that they generate an array of useful bioactive compounds which have health benefits such as significant antioxidant activities. In this study, an in vitro culture system has been developed, which could be explored to extract high-value bioactive compounds from feijoa. Feijoa tissue culture was initiated by the induction of callus from floral buds. Sections of floral buds were plated on MS medium supplemented with 2,4-D and BAP at 2.0mg/L and 0.2mg/L concentrations, respectively. Cell suspension cultures of feijoa were established using a liquid MS medium with different concentrations of 2,4-D and BAP and cultured on a rotary shaker. The growth of the cell suspension was evaluated with different parameters such as different carbohydrate sources, concentration of MS media, and inoculum density. When the cell suspensions were treated with different concentrations of MeJA at different time points, phytochemicals UPLC - QTOF MS analysis identified extractables of interest. The main compounds identified were secondary metabolites (flavonoids and flavonoid-glucosides) and plant hormones. These compounds are of interest for their potential use in therapeutics or skin and personal care products. This report investigates essential methodology parameters for establishing cell suspension cultures from feijoa floral buds, which could be used to generate in vitro biomass to produce high-value bioactive compounds. This is the first study reporting the identification of arctigenin from feijoa, a high-value compound whose pharmaceutical properties, including anti-tumour, anti-inflammatory and anti-colitis effects, have been widely reported. The ability of feijoa cell cultures to produce such high-value bioactive compounds is extremely promising for its use in pharmaceuticals, cosmeceuticals and nutraceuticals applications.

Design, Synthesis, and Biological Evaluation of Novel Camphor-Based Hydrazide and Sulfonamide Derivatives as Laccase Inhibitors against Plant Pathogenic Fungi/Oomycetes

To discover novel natural product-based fungicidal agrochemicals, 41 novel camphanic acid hydrazide and camphor sulfonamide derivatives were designed, synthesized, and tested for their antifungal profile against four plant pathogenic fungi and three oomycetes. As a result, some derivatives presented pronounced inhibitory activities toward Botryosphaeria dothidea, Fusarium graminearum, Phytophthora capsici, and Phytophthora nicotianae. Especially, compound 4b demonstrated the most potent anti-B. dothidea activity (EC50 = 1.28 mg/L), much stronger than positive control chlorthalonil. The in vivo assay showed that 4b displayed significant protective and curative effects on apple fruits infected by B. dothidea. The primary antifungal mechanism study revealed that 4b could obviously enhance the cell membrane permeability, destroy the mycelial surface morphology and the cell ultrastructure, and reduce the ergosterol and exopolysaccharide contents of B. dothidea. Further, 4b showed potent laccase inhibitory activity in vitro with an IC50 value of 11.3 μM, superior to positive control cysteine. The molecular docking study revealed that 4b could dock well into the active site of laccase by forming multiple interactions with the key residues in the pocket. The acute oral toxicity test in rats presented that 4b had slight toxicity with an LD50 value of 849.1 mg/kg bw (95% confidence limit: 403.9-1785.3 mg/kg bw). This research identified that the camphanic acid hydrazide derivatives could be promising leads for the development of novel laccase-targeting fungicides.

Modes-of-action of antifungal compounds: Stressors and (target-site-specific) toxins, toxicants, or Toxin-stressors

Fungi and antifungal compounds are relevant to the United Nation's Sustainable Development Goals. However, the modes-of-action of antifungals-whether they are naturally occurring substances or anthropogenic fungicides-are often unknown or are misallocated in terms of their mechanistic category. Here, we consider the most effective approaches to identifying whether antifungal substances are cellular stressors, toxins/toxicants (that are target-site-specific), or have a hybrid mode-of-action as Toxin-stressors (that induce cellular stress yet are target-site-specific). This newly described 'toxin-stressor' category includes some photosensitisers that target the cell membrane and, once activated by light or ultraviolet radiation, cause oxidative damage. We provide a glossary of terms and a diagrammatic representation of diverse types of stressors, toxic substances, and Toxin-stressors, a classification that is pertinent to inhibitory substances not only for fungi but for all types of cellular life. A decision-tree approach can also be used to help differentiate toxic substances from cellular stressors (Curr Opin Biotechnol 2015 33: 228-259). For compounds that target specific sites in the cell, we evaluate the relative merits of using metabolite analyses, chemical genetics, chemoproteomics, transcriptomics, and the target-based drug-discovery approach (based on that used in pharmaceutical research), focusing on both ascomycete models and the less-studied basidiomycete fungi. Chemical genetic methods to elucidate modes-of-action currently have limited application for fungi where molecular tools are not yet available; we discuss ways to circumvent this bottleneck. We also discuss ecologically commonplace scenarios in which multiple substances act to limit the functionality of the fungal cell and a number of as-yet-unresolved questions about the modes-of-action of antifungal compounds pertaining to the Sustainable Development Goals.

Antibiofilm and Antivirulence Activities of Gold and Zinc Oxide Nanoparticles Synthesized from Kimchi-Isolated Leuconostoc sp. Strain C2

The rapid emergence of antimicrobial resistance (AMR) among bacterial pathogens results in antimicrobial treatment failure and the high mortality rate associated with AMR. The application of nanoparticles synthesized from probiotics will be widely accepted due to their efficacy and biocompatibility in treating microbial infections in humans. The current work sought to isolate and identify lactic acid bacteria (LAB) from Kimchi. Based on 16S rRNA gene sequencing, the LAB isolate C2 was identified as a member of the genus Leuconostoc. The obtained supernatant from Leuconostoc sp. strain C2 was employed for the green synthesis of metal (AuNPs) and metal oxide (ZnONPs) nanoparticles. UV–vis absorption spectra, FTIR analysis, XRD, DLS, FE-TEM, and EDS mapping were used to fully characterize these C2-AuNPs and C2-ZnONPs. The C2-AuNPs were found to be spherical in shape, with a size of 47.77 ± 5.7 nm and zeta potential of −19.35 ± 0.67 mV. The C2-ZnONPs were observed to be rod-shaped and 173.77 ± 14.53 nm in size. The C2-ZnONPs zeta potential was determined to be 26.62 ± 0.35 mV. The C2-AuNPs and C2-ZnONPs were shown to have antimicrobial activity against different pathogens. Furthermore, these nanoparticles inhibited the growth of Candida albicans. The antibiofilm and antivirulence properties of these NPs against Pseudomonas aeruginosa and Staphylococcus aureus were thoroughly investigated. C2-AuNPs were reported to be antibiofilm and antivirulence against P. aeruginosa, whereas C2-ZnONPs were antibiofilm and antivirulence against both P. aeruginosa and S. aureus. Furthermore, these nanoparticles disrupted the preformed mature biofilm of P. aeruginosa and S. aureus. The inhibitory impact was discovered to be concentration-dependent. The current research demonstrated that C2-AuNPs and C2-ZnONPs exhibited potential inhibitory effects on the biofilm and virulence features of bacterial pathogens. Further studies are needed to unravel the molecular mechanism behind biofilm inhibition and virulence attenuation.

Phenolic-rich feijoa extracts from flesh, peel and whole fruit activate apoptosis pathways in the LNCaP cell line

This study aimed to explore the potential anticancer activity of phenolic-rich feijoa extracts from the flesh, peel, and whole fruit on the human prostate cancer cell line (LNCaP). Results showed that feijoa extracts had cancer-specific anti-proliferative activity on the LNCaP cell line. The anticancer activity of feijoa extracts was shown through activation of the caspase-dependent apoptosis pathway based on the increase of sub-G1 phase in the cell cycle, the decrease of mitochondrial membrane potential, as well as the elevated caspase 3, 8, and 9 activity in the treated LNCaP cells. The anti-cancer activity of feijoa extracts could be attributed to the high total phenolic contents (0.14-0.37 mg GAE/mg dw) and, in particular, the high ellagic acid content (2.662-9.119 μg/mg dw). The successful activation of the caspase-dependent apoptosis pathway indicates that phenolic-rich feijoa extracts have a good potential to be utilized as a functional ingredient in foods and nutraceuticals.

Discovery of Novel 3,4-Dichloroisothiazole-Containing Coumarins as Fungicidal Leads

Natural products are one of the resources for discovering novel fungicidal leads. As a natural fungicide, osthole was used as a coumarin-based lead compound for the development of novel fungicides. Here, a series of 3,4-dichloroisothiazole-containing 7-hydroxycoumarins were rationally designed, synthesized, and characterized by introducing a bioactive substructure, 3,4-dichloroisothiazole, into the coumarin skeleton. In vitro bioassay indicated that compound 7g displayed good activity against Rhizoctonia solani, Physalospora piricola, Sclerotinia sclerotiorum, and Botrytis cinerea. Its median effective concentration (EC₅₀) value against each of these fungi fell between 0.88 and 2.50 μg/mL, which was much lower than that of osthole against the corresponding pathogen (between 7.38 and 74.59 μg/mL). In vivo screening validated that 7k exhibited 100%, 60%, and 20% efficacy against R. solani Kühn at 200, 100, and 50 μg/mL, respectively. RNA sequence analysis implied that growth inhibition of R. solani by 7k might result from potential disruptions of fungal membrane formation and intracellular metabolism. Furthermore, a field experiment with cucumber plants indicated that 7b showed 62.73% and 74.03% efficacy against Pseudoperonospora cubensis (Berk. & Curt.) Rostov. at rates of 12.5 g a.i./ha and 25 g a.i./ha, respectively, which showed no significant difference between 7b and osthole at 30 g a.i./ha. Our studies suggested that 7b, 7g, and 7k might be used as fungicidal leads for further optimization.

Insights into the Inhibition of Aeromonas hydrophila d-Alanine-d-Alanine Ligase by Integration of Kinetics and Structural Analysis

Aeromonas hydrophila, a pathogenic bacterium, is harmful to humans, domestic animals, and fishes and, moreover, of public health concern due to the emergence of multiple drug-resistant strains. The cell wall has been discovered as a novel and efficient drug target against bacteria, and d-alanine-d-alanine ligase (Ddl) is considered as an essential enzyme in bacterial cell wall biosynthesis. Herein, we studied the A. hydrophila HBNUAh01 Ddl (AhDdl) enzyme activity and kinetics and determined the crystal structure of AhDdl/d-Ala complex at 2.7 Å resolution. An enzymatic assay showed that AhDdl exhibited higher affinity to ATP (K_m: 54.1 ± 9.1 μM) compared to d-alanine (K_m: 1.01 ± 0.19 mM). The kinetic studies indicated a competitive inhibition of AhDdl by d-cycloserine (DCS), with an inhibition constant (K_i) of 120 μM and the 50% inhibitory concentrations (IC₅₀) value of 0.5 mM. Meanwhile, structural analysis indicated that the AhDdl/d-Ala complex structure adopted a semi-closed conformation form, and the active site was extremely conserved. Noteworthy is that the substrate d-Ala occupied the second d-Ala position, not the first d-Ala position. These results provided more insights for understanding the details of the catalytic mechanism and resources for the development of novel drugs against the diseases caused by A. hydrophila.

Antifungal Mechanism of Dipicolinic Acid and Its Efficacy for the Biocontrol of Pear Valsa Canker

Valsa pyri is a fatal canker pathogen that causes significant reduction of crop yield in pear orchards. V. pyri invades the trunk phloem, and is difficult to control by chemical treatment. In this work, it was found for the first time that Bacillus subtilis-produced dipicolinic acid (DPA) exhibits antifungal activity against different canker pathogens, including Alteraria alternata, Botryosphaeria dothidea, Rhizoctonia solani, and V. pyri. Growth inhibition of V. pyri was observed at less than 5 mM concentration (pH = 5.6). DPA showed the highest antifungal activity at acidic pH values and in the presence of bivalent metals, such as zinc(II), cobalt(II), and copper(II). Measurement of mRNA expression levels and scanning electron microscope (SEM) observations revealed that DPA causes V. pyri apoptosis via inhibition of chitin biosynthesis and subsequent cell lysis. Interestingly, DPA showed high stability in the pear bark and was able to cross the pear tree bark into the phloem, protecting the internal phases of the pear trunk. In preventive applications, DPA reduced the canker symptoms of V. pyri on Cuigan pear trees by 90%. Taken together, an efficient strategy for the management of V. pyri-caused canker disease was developed using a novel antifungal agent, DPA, with strong antifungal activity and particular diffusion properties.

Feijoa Fruit Peel: Micro-morphological Features, Evaluation of Phytochemical Profile, and Biological Properties of Its Essential Oil

Acca sellowiana (O. Berg) Burret (Feijoa) is an evergreen shrub, belonging to the Mirtaceae family. The aim of this study was to investigate the micromorphological features of the feijoa fruit peel and to evaluate the phytochemical profile, as well as the antioxidant, cytoprotective, and antimicrobial properties of its essential oil (EO), by several in vitro cell-free and cell-based assays. The micromorphological analysis showed several schizogenic secretory cavities, immediately below the epidermal layer. Forty compounds were identified and quantified by GC-FID and GC-MS analyses. Sesquiterpenes were the most abundant ones (76.89%), followed by monoterpene hydrocarbons (3.26%), and oxygenated monoterpenes (0.34%). The main compounds were γ-Selinene (17.39%), α-Cariophyllene (16.74%), β-Cariophyllene (10.37%), and Germacene D (5.32%). The EO showed a strong and dose-dependent antioxidant, and free-radical scavenging activity. Furthermore, it showed cytoprotective activity on the lymphocytes, that have been pre-treated with 100 μM tert-butyl-hydroperoxide (t-BOOH), as well as a decrease in intracellular reactive oxygen species (ROS), induced by t-BOOH on erythrocytes. A preliminary antimicrobial screening against GRAM+ and GRAM− bacteria, as well as on fungi highlighted that EO showed the best activity against S. aureus and C. albicans (MIC 2.7 mg/mL). In light of these results, feijoa fruit EO could find various applications, especially in the food, nutraceutical, and pharmaceutical fields.

Extraction Optimization, Antioxidant Capacity and Phenolic Profiling of Extracts from Flesh, Peel and Whole Fruit of New Zealand Grown Feijoa Cultivars

Feijoa fruit is becoming increasingly popular, yet limited studies have focused on the antioxidant capacity and phenolic profiling of its extracts. In this research, optimization of phenolic extraction from feijoa flesh, peel, and whole fruit from four New Zealand grown cultivars was conducted using orthogonal design. Antioxidant activities of the extracts were assessed, followed by phenolic profiling by a validated liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method. For feijoa flesh and whole fruit, the extraction was optimized using 70% ethanol, material to solvent ratio of 1:30, at extraction temperature of 50 °C for 30 min. For feijoa peel, extraction at 50 °C for 60 min using 50% ethanol with a material to solvent ratio of 1:30 were the optimized conditions. Results showed feijoa peel had higher total phenolic content (TPC) and antioxidant activities than the flesh and whole fruit. Overall, the Unique cultivar had a relatively higher TPC and antioxidant activity than the other cultivars tested. A total of 15 phenolic compounds were identified, and seven of them were reported for the first time in feijoa fruit. This is the first systematic investigation on the extraction method, phenolic content, antioxidant activity and phenolic profile of feijoa emphasis on comparison of sample types and cultivars.

Synthesis of functionalized cyclopentenes through allenic ketone-based multicomponent reactions

A novel and efficient synthesis of diversely functionalized cyclopentene derivatives through the multicomponent reactions of 1,2-allenic ketones with 4-chloroacetoacetate and malononitrile/cyanoacetate under mild and metal-free conditions is presented. Mechanistically, the formation of title compounds involves a cascade process including nucleophilic substitution, Michael addition and intramolecular aldol type reaction. Interestingly, when 1-phenyl allenic ketones bearing electron-donating groups on the phenyl ring were reacted with 4-chloroacetoacetate and cyanoacetate, methylenecyclo-pentanes, the regioisomer of cyclopentenes, were formed with good selectivity and high efficiency.