Antifungal activity of resveratrol against Botrytis cinerea is improved using 2-furyl derivatives

UV-exposure decreases antimicrobial activities of a grapevine cane extract against Plasmopara viticola and Botrytis cinerea as a consequence of stilbene modifications-a kinetic study

BACKGROUND

Stilbenoid extracts, such as those originating from grapevine by-products (e.g. canes), are of interest for use as biopesticides in vineyard owing to their antimicrobial activities. However, stilbenoids are unstable in the environment, especially under light. This study aimed to chemically characterize the effect of UV light on stilbenoids present in a grapevine cane extract (CE), and to evaluate the antimicrobial activities against two major grapevine pathogens (Plasmopara viticola and Botrytis cinerea) of grapevine extracts exposed to UV.

RESULTS

Treatment with UV (365 nm) on a grapevine CE led to degradation of stilbenoids (up to 71% after 1 h). The stilbenoid stability depended on their chemical structure: only those possessing CC, as trans-resveratrol and trans-ε-viniferin, were affected with first their isomerization and secondly their oxidation/cyclization. As a consequence, UV-exposed extracts (UV-CEs) showed reduced antimicrobial activities against the two pathogens (mycelium and spores). For instance, regarding P. viticola, an UV-CE exposed during 4 h showed an almost total loss of its activity on oomycete development and a 2.4-fold inhibition of zoospore mobility in comparison to CE. For B. cinerea, the inhibition capacity of the same UV-CE was reduced by only 1.1-fold on mycelial development and by 3.2-fold on conidial germination compared to CE.

CONCLUSION

UV light triggered modifications on the structure of bioactive stilbenoids, resulting in losses of their antimicrobial activities. Photoprotection of stilbenoids has to be considered in the perspective of using them in vineyards as biopesticides. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Stereodivergent Zweifel Olefination and its Mechanistic Dichotomy

Stereoselective Zweifel olefination using boronate complexes carrying two different reactive π-systems was achieved to synthesize vinyl heteroarenes and conjugated 1,3-dienes in good yield and up to 100 % stereoselectivity, which remains unexplored until now. Most importantly, we report the unprecedented formation of E vs. Z-vinyl heteroarenes for different heteroarenes under identical conditions. Density functional theory (DFT) investigations unveil the mechanistic dichotomy between olefin and heteroarene activation followed by 1,2-migration, leading to E or Z-vinyl heteroarenes respectively. We also report a previously unknown reversal of stereoselectivity by using 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an electrophile. The Zweifel olefination using a boronate complex that carries two different olefins was previously unexplored due to significant challenges associated with the site-selective activation of olefins. We have solved this problem and reported the site-selective activation of olefins for the stereoselective synthesis of 1,3-dienes.

Carboxymethyl chitosan-quercetin conjugate: A sustainable one-step synthesis and use for food preservation

Bioactive polysaccharide, carboxymethyl chitosan-quercetin (CMCS-q) was prepared by a one-step reaction utilizing Schiff base chemistry. Notably, the presented conjugation method involves neither radical reactions nor auxiliary coupling agents. Physicochemical properties and bioactivity of the modified polymer were studied and compared to those of the pristine carboxymethyl chitosan, CMCS. The modified CMCS-q demonstrated antioxidant activity by TEAC assay and antifungal activity by inhibiting spore germination of plant pathogen Botrytis cynerea. Then, CMCS-q was applied as an active coating on fresh-cut apples. The treatment resulted in enhanced firmness, inhibited browning and improved microbiological quality of the food product. The presented conjugation method allows retaining antimicrobial and antioxidant activity of quercetin moiety in the modified biopolymer. This method can be further used as a platform for binding ketone/aldehyde-containing polyphenols and other natural compounds to form various bioactive polymers.

Antifungal Activities of a Grapevine Byproduct Extract Enriched in Complex Stilbenes and Stilbenes Metabolization by Botrytis cinerea

Grapevine co-products, as canes, represent a source of compounds of interest to control vineyard diseases with a sustainable approach. We chose to study an extract that we produced from grapevine trunk and roots. This extract, enriched in complex stilbenes, strongly reduced mycelial growth and spore germination of Botrytis cinerea, the fungal agent causing gray mold. The most active stilbenes were resveratrol, r-viniferin, and ε-viniferin. This grapevine extract also inhibited the production of Botrytis laccases. Conversely, Botrytis secretome metabolized resveratrol into δ-viniferin and pallidol (2 dimers); and ε-viniferin, a dimer, into hopeaphenol, r-viniferin, and r2-viniferin (3 tetramers). r-Viniferin and hopeaphenol (2 tetramers) were not metabolized. The biotransformed extract maintained an effective antimycelial activity. This study provides evidence that a grapevine extract enriched in oligomerized stilbenes exerts different anti-Botrytis activities, notwithstanding the ability of the fungus to metabolize some stilbenes.

Antifungal activity against anthracnose-causing species of homopterocarpin derivatives

Derivatives of 3,9-dimethoxypterocarpan (1, homopterocarpin) were prepared by nitration, amination, and oxidation reactions, among others, and their antifungal activity was evaluated against the phytopathogenic fungi Colletotrichum gloeosporioides and C. lindemuthianum. Derivatives were purified by chromatographic techniques and identified by nuclear magnetic resonance spectroscopy. Eight derivatives were obtained from 1 corresponding to 3,9-dimethoxy-8-nitropterocarpan (2), 3,9-dimethoxy-2,8-dinitropterocarpan (3), 3,9-dimethoxy-2,8,10-trinitropterocarpan (4), 2,8-diamino-3,9-dimethoxypterocarpan (5), 3,9-dimethylcoumestan (6), medicarpin (7), 2'-hydroxy-4-(2-hydroxyethylsulfanyl)-7,4'-dimethoxyisoflavan (8), and 4-(2-hydroxyethylsulfanyl)-7,2',4'-trimethoxyisoflavan (9). The in vitro antifungal activity of the derivatives was determined at concentrations between 35 and 704 μM. Compounds 7 and 8 at 704 μM, showed an inhibition of radial growth and spore germination close to 100%, exceeding that found for the starting compound 1, which was 46%. Growth inhibition assays were also performed for the derivative 8 on papaya fruits (Carica papaya L. cv. Hawaiana) and mango (Mangifera indica L. cv. Hilacha) infected with C. gloeosporioides. Compound 8 showed fungal growth inhibition in fruits higher than that found for 1 and thymol (a recognized natural antifungal), under the same conditions. In general, derivatives that exhibited greater antifungal activity correspond to the compounds containing hydroxyl groups in the structure. Some of the compounds obtained could be considered promising for the control of phytopathogenic fungi.

Identification and structural elucidation of bioactive compounds from Scirpoides holoschoenus

Phytochemical investigations of dichloromethane and methanol extracts of roots and rhizomes of Scirpoides holoschoenus afforded 21 stilbenes, six flavonoids, six ferulic acid derivatives and four diterpenes. Among these constituents, six stilbenes, one flavonoid, one diterpene and two ferulic acid derivatives, represent previously unreported natural products. Structure elucidation was performed by HRESI-MS, NMR, GC-MS, and ECD data evaluation. The monoprenylated flavonoid (sophoraflavanone B) and all isolated stilbene oligomers (trans-scirpusin B, scirpusin A, cassigarol E, cyperusphenol B, cyperusphenol D, passiflorinol A, cyperusphenol A and mesocyperusphenol A) showed strong inhibitory activities on spore germination of two Botrytis cinerea strains isolated from field-infected grape berries and apple fruits compared to the reference controls resveratrol, piceid, and fenhexamid at a test concentration of 2.0 mM. For sophoraflavanone B and cyperusphenol A, the EC₅₀ values were determined by concentration response curves and resulted in values of 0.35 mM and 0.53 mM, respectively. The data suggest that stilbene oligomers but also prenylated flavonoids should be examined further to gain more information on their antimicrobial activity and might be a suitable addition to chemical fungicides on the market to combat gray mold.

Chemically Tuning Resveratrol for the Effective Killing of Gram-Positive Pathogens

In the era of antimicrobial resistance, the identification of new compounds with strong antimicrobial activity and the development of alternative therapies to fight drug-resistant bacteria are urgently needed. Here, we have used resveratrol, a safe and well-known plant-derived stilbene with poor antimicrobial properties, as a scaffold to design several new families of antimicrobials by adding different chemical entities at specific positions. We have characterized the mode of action of the most active compounds prepared and have examined their synergistic antibacterial activity in combination with traditional antibiotics. Some alkyl- and silyl-resveratrol derivatives show bactericidal activity against Gram-positive bacteria in the same low micromolar range of traditional antibiotics, with an original mechanism of action that combines membrane permeability activity with ionophore-related activities. No cross-resistance or antagonistic effect was observed with traditional antibiotics. Synergism was observed for some specific general-use antibiotics, such as aminoglycosides and cationic antimicrobial peptide antibiotics. No hemolytic activity was observed at the active concentrations or above, although some low toxicity against an MRC-5 cell line was noted.

Stilbenes: Characterization, bioactivity, encapsulation and structural modifications. A review of their current limitations and promising approaches

Stilbenes are phenolic compounds naturally synthesized as secondary metabolites by the shikimate pathway in plants. Research on them has increased in recent years due to their therapeutic potential as antioxidant, antimicrobial, anti-inflammatory, anticancer, cardioprotective and anti-obesity agents. Amongst them, resveratrol has attracted the most attention, although there are other natural and synthesized stilbenes with enhanced properties. However, stilbenes have some physicochemical and pharmacokinetic problems that need to be overcome before considering their applications. Human clinical evidence of their bioactivity is still controversial due to this fact and hence, exhaustive basis science on stilbenes is needed before applied science. This review gathers the main physicochemical and biological properties of natural stilbenes, establishes structure-activity relationships among them, emphasizing the current problems that limit their applications and presenting some promising approaches to overcome these issues: the encapsulation in different agents and the structural modification to obtain novel stilbenes with better features. The bioactivity of stilbenes should move from promising to evident.

Quaternized chitosan as a biopolymer sanitizer for leafy vegetables: synthesis, characteristics, and traditional vs. dry nano-aerosol applications

A series of quaternary dimethyl-(alkyl)-ammonium chitosan derivatives (QACs) was synthesized and studied for physicochemical properties and bioactivity. The QACs tended to spontaneously self-assembly into nanoaggregates. Antimicrobial activity was examined in vitro on Gram-negative Escherichia coli (E. coli) and Gram-positive Listeria innocua (L. innocua) bacteria as well as phytopathogenic fungus Botrytis cinerea. The hexyl chain-substituted QAC-6 demonstrated the highest potency causing 3.0- and 4.5-log CFU mL-1 reduction of E. coli and L. innocua, respectively. QAC-6 was tested for antimicrobial activity on stainless steel coupons and fresh spinach leaves. A traditional 'wet' application (spray) and dry Engineered Water Nanostructure (EWNS) approach were used for spinach decontamination. With both approaches, significant reduction of microbial load on the treated produce was achieved. The wet application showed a greater reduction of microbial load, while the advantages of EWNS were reaching the antimicrobial effect with miniscule dose of active agent leaving treated surface visibly dry.

Resveratrol and cyclodextrins, an easy alliance: Applications in nanomedicine, green chemistry and biotechnology

Most drugs or the natural substances reputed to display some biological activity are hydrophobic molecules that demonstrate low bioavailability regardless of their mode of absorption. Resveratrol and its derivatives belong to the chemical group of stilbenes; while stilbenes are known to possess very interesting properties, these are limited by their poor aqueous solubility as well as low bioavailability in animals and humans. Among the substances capable of forming nanomolecular inclusion complexes which can be used for drug delivery, cyclodextrins show spectacular physicochemical and biomedical implications in stilbene chemistry for their possible application in nanomedicine. By virtue of their properties, cyclodextrins have also demonstrated their possible use in green chemistry for the synthesis of stilbene glucosylated derivatives with potential applications in dermatology and cosmetics. Compared to chemical synthesis and genetically modified microorganisms, plant cell or tissue systems provide excellent models for obtaining stilbenes in few g/L quantities, making feasible the production of these compounds at a large scale. However, the biosynthesis of stilbenes is only possible in the presence of the so-called elicitor compounds, the most commonly used of which are cyclodextrins. We also report here on the induction of resveratrol production by cyclodextrins or combinatory elicitation with methyljasmonate in plant cell systems as well as the mechanisms by which they are able to trigger a stilbene response. The present article therefore discusses the role of cyclodextrins in stilbene chemistry both at the physico-chemical level as well as the biomedical and biotechnological levels, emphasizing the notion of "easy alliance" between these compounds and stilbenes.

Inhibitory activity of stilbenes against filamentous fungi

Stilbenoids (resveratrol and its derivatives) are secondary metabolites produced by plants as defence mechanism to microbial infection. These compounds are known for their anti-inflammatory action and health benefits in preventing a wide range of disorders (e.g. cancer and cardiovascular diseases). However, their antimicrobial properties are less investigated. A series of 8 stilbenoid compounds were synthesized and their antifungal activity against 19 wild strains of filamentous fungi and yeasts (isolated from the environment and food) was tested in vitro. Using an agar diffusion assay, compounds were tested at the concentration of 100 μg/ml on filamentous fungi and yeasts at 10⁴ CFU/ml. The results showed that tested derivatives possess moderate antifungal activity: in particular, monomeric stilbenoids 3'-hydroxy-pterostilbene and piceatannol, and dimeric stilbenoids (±)-trans-δ-viniferin and pallidol were active against mycotoxigenic fungi.

A Comprehensive Study on the Antimicrobial Properties of Resveratrol as an Alternative Therapy

Resveratrol is a polyphenolic antioxidant whose possible health benefits include anticarcinogenic, antiaging, and antimicrobial properties that have gained significant attention. The compound is well accepted by individuals and has been commonly used as a nutraceutical in recent decades. Its widespread usage makes it essential to study as a single agent as well as in combination with traditional prescription antibiotics as regards to antimicrobial properties. Resveratrol demonstrates the action of antimicrobials against a remarkable bacterial diversity, viruses, and fungus. This report explains resveratrol as an all-natural antimicrobial representative. It may modify the bacterial virulence qualities resulting in decreased toxic substance production, biofilm inhibition, motility reduction, and quorum sensing disturbance. Moreover, in conjunction with standard antibiotics, resveratrol improves aminoglycoside efficacy versus Staphylococcus aureus, while it antagonizes the deadly function of fluoroquinolones against S. aureus and also Escherichia coli. The present study aimed to thoroughly review and study the antimicrobial potency of resveratrol, expected to help researchers pave the way for solving antimicrobial resistance.

Can the cavi-precipitation process be exploited to generate smaller size drug nanocrystal?

OBJECTIVE

Cavi-precipitation has the potential to generate drug nanocrystals very efficiently. Achieving smaller than 100 nm particle size for organic drug substances still remained a challenge. The objective of this study was to demonstrate if cavi-precipitation technology can be used to generate smaller than 100 nm drug nanocrystal particle.

SIGNIFICANCE

This study demonstrates that cavi-precipitation process can be used to generate drug nanocrystals of the model compound resveratrol (RVT) consists of crystallites of 30-50 nm size.

METHOD

RVT was dissolved in different organic solvents to prepare the solvent phase (S-phase). Several stabilizers were tested for the organic phase. A combination of SDS and PVP was used stabilizer system in the aqueous anti-solvent phase (AS-phase). The S-phase was added to the AS-phase inside the Emulsiflex C5 homogenizer. Nanosuspension was characterized by laser diffractometry (LD), photon correlation spectroscopy (PCS) and scanning electron microscopy (SEM). The solid state of the suspended particles was investigated by powder X-ray diffractometry (PXRD) and differential scanning calorimetry (DSC).

RESULTS

It was found that DMSO, alone or in combination with acetone in the S-Phase generated the smallest size RVT nanocrystals. The optimum solvent (S) antisolvent (AS) ratio (S:AS) was found to be 3.6:56.4 (v:v). Span 20 was identified as the best stabilizer for the organic phase at a ratio (w:w) of 1:3 (Span 20:RVT). The particles precipitated from different solvents were predominantly crystalline.

CONCLUSIONS

The best sample had a mean particle size (LD) of 167 nm [d(0.5)] which was composed of smaller crystallites having 30-50 nm size (SEM).

Isothiocyanate Derivatives of Glucosinolates as Efficient Natural Fungicides

Fungal pathogens on crops account for losses that exceed US$200 billion annually. At present, chemical fungicides are widely used in the agricultural industry. Many of these products have a detrimental effect on human and animal health and are consequently forbidden postharvest, especially in Europe. Despite efforts to develop natural crop protection, very few have been commercialized. We explored the physicochemical characteristics of (i) glucosinolate derivatives from the present study and previously published papers in the light of their known biological roles and (ii) fungitoxic glucosinolate derivatives compared with natural and chemical fungicides. We found that 13 out of 31 tested natural and semisynthetic isothiocyanates are efficient fungicides against widespread species of plant pathogens alone and in a synergistic manner. Interestingly, physicochemical characteristics of fungitoxic glucosinolate derivatives differ from those showing no activities or known for their insecticidal or insect-attractive properties. The comparison of physicochemical characteristics of natural and semisynthetic fungitoxic glucosinolate derivatives with other fungicides (natural, semisynthetic, and synthetic) revealed that isothiocyanate glucosinolate derivatives clustered with nonglucosinolate derivatives plant fungicides as well as with some synthetic ones. Most of the fungicides show high bioaccumulation potential and lipophilic properties that most likely allow them to go through membranes.

[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Disarming the Host: Detoxification of Plant Defense Compounds During Fungal Necrotrophy

While fungal biotrophs are dependent on successfully suppressing/subverting host defenses during their interaction with live cells, necrotrophs, due to their lifestyle are often confronted with a suite of toxic metabolites. These include an assortment of plant defense compounds (PDCs) which can demonstrate broad antifungal activity. These PDCs can be either constitutively present in plant tissue or induced in response to infection, but are nevertheless an important obstacle which needs to be overcome for successful pathogenesis. Fungal necrotrophs have developed a number of strategies to achieve this goal, from the direct detoxification of these compounds through enzymatic catalysis and modification, to the active transport of various PDCs to achieve toxin sequestration and efflux. Studies have shown across multiple pathogens that the efficient detoxification of host PDCs is both critical for successful infection and often a determinant factor in pathogen host range. Here, we provide a broad and comparative overview of the various mechanisms for PDC detoxification which have been identified in both fungal necrotrophs and fungal pathogens which depend on detoxification during a necrotrophic phase of infection. Furthermore, the effect that these mechanisms have on fungal host range, metabolism, and disease control will be discussed.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Antioxidant and Biological Activities of Hydroxytyrosol and Homovanillic Alcohol Obtained from Olive Mill Wastewaters of Extra-Virgin Olive Oil Production

Some constituents of the Mediterranean diet, such as extra-virgin olive oil (EVOO) contain substances such as hydroxytyrosol (HT) and its metabolite homovanillic alcohol (HA). HT has aroused much interest due to its antioxidant activity as a radical scavenger, whereas only a few studies have been made on the HA molecule. Both chemical synthesis and extraction techniques have been developed to obtain these molecules, with each method having its advantages and drawbacks. In this study, we report the use of tyrosol from olive mill wastewaters as a starting molecule to synthesize HT and HA, using a sustainable procedure characterized by high efficiency and low cost. The effects of HT and HA were evaluated on two cell lines, THP-1 human leukemic monocytes and L-6 myoblasts from rat skeletal muscle, after treating the cells with a radical generator. Both HT and HA efficiently inhibited ROS production. In particular, HT inhibited the proliferation of the THP-1 leukemic monocytes, while HA protected L-6 myoblasts from cytotoxicity.

Secondary metabolites as plant defensive strategy: a large role for small molecules in the near root region

The roles of plant roots are not merely limited to the provision of mechanical support, nutrients and water, but also include more specific roles, such as the capacity to secrete diverse chemical substances. These metabolites are actively secreted in the near root and play specific and significant functions in plant defense and communication. In this review, we detail the various preventive roles of these powerful substances in the rhizosphere with a perspective as to how plants recruit microbes as a preventive measure against other pathogenic microbes, also, briefly about how the rhizosphere can repel insect pests, and how these chemical substances alter microbial dynamics and enhance symbiotic relationships. We also highlight the need for more research in this area to detail the mode of action and quantification of these compounds in the environment and their roles in some important biological processes in microorganisms and plants.

Antifungal Activity of Eugenol Derivatives against Botrytis Cinerea

Botrytis cinerea is a worldwide spread fungus that causes the grey mold disease, which is considered the most important factor in postharvest losses in fresh fruit crops. Consequently, the control of gray mold is a matter of current and relevant interest for agricultural industries. In this work, a series of phenylpropanoids derived from eugenol were synthesized and characterized. Their effects on the mycelial growth of a virulent and multi-resistant isolate of B. cinerea (PN2) have been evaluated and IC₅₀ values for the most active compounds range between 31⁻95 ppm. The antifungal activity exhibited by these compounds is strongly related to their chemical structure, i.e., increasing activity has been obtained by isomerization of the double bond or introduction of a nitro group on the aromatic ring. Based on the relationship between the fungicide activities and chemical structure, a mechanism of action is proposed. Finally, the activity of these compounds is higher than that reported for the commercial fungicide BC-1000 that is currently employed to combat this disease. Thus, our results suggest that these compounds are potential candidates to be used in the design of new and effective control with inspired natural compounds of this pathogen.

Stilbene derivatives as new perspective in antifungal medicinal chemistry

The high incidence and mortality of invasive fungal infections and serious drug resistance have become a global public health issue. There is an urgent need for alternative antimicrobials to control fungal infections and targeting it by antifungal substances from the natural sources represents a promising new strategy for the development of novel antifungal agents. Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a phytoalexin produced by plant species in response to environmental stress or pathogenic attacks. It has many known and potential therapeutic applications in human general homeostasis; it mediates a great number of biological responses relevant for human health such as anticancer, cardio and neuroprotective, antioxidant, and antimicrobial activities. Resveratrol is a natural antifungal agent, therefore it can be considered as a scaffold for designing structural relatives potentially capable of mediating more intense responses in a more specific way. Also, stilbenes produced by several plants may be useful lead structure for the chemical synthesis of antifungal. Their antifungal potential represents a useful solution to the drug resistance and side effect complications that occur after pharmacological treatment of infectious diseases. The purpose of this review is to present an overview on resveratrol derivatives, both natural and synthetic, with antifungal activity and summarize the chemical structure and the therapeutic versatility of stilbene-containing compounds.

Antifungal Activity against Botrytis cinerea of 2,6-Dimethoxy-4-(phenylimino)cyclohexa-2,5-dienone Derivatives

In this work the enzyme laccase from Trametes versicolor was used to synthetize 2,6-dimethoxy-4-(phenylimino)cyclohexa-2,5-dienone derivatives. Ten products with different substitutions in the aromatic ring were synthetized and characterized using ¹H- and 13C-NMR and mass spectrometry. The 3,5-dichlorinated compound showed highest antifungal activity against the phytopathogen Botrytis cinerea, while the p-methoxylated compound had the lowest activity; however, the antifungal activity of the products was higher than the activity of the substrates of the reactions. Finally, the results suggested that these compounds produced damage in the fungal cell wall.

Detoxification Mechanism of 8,8-Dimethyl-3-[(R-phenyl)amino]-1,4,5(8H)-naphthalentrione Derivatives by Botrytis cinerea

The effect of 8,8-dimethyl-3-[(R-phenyl)amino]-1,4,5(8H)-naphthalentrione derivatives (compounds 1⁻13) on the mycelial growth of Botrytis cinerea was evaluated. The fungitoxic effect depended on the substituent and its position in the aromatic ring. Compounds substituted with halogens in meta and/or para positions (compounds 3, 4, 5 and 7), methyl (compounds 8 and 9), methoxyl (compounds 10 and 11), or ethoxy-carbonyl groups (compound 12) presented higher antifungal activity than compound 1, which had an unsubstituted aromatic ring. In addition, compounds with halogens in the ortho position, such as compounds 2 and 6, and a substitution with an acetyl group in the para position (compound 13) were less active. The role of the ABC efflux pump Bctr B-type as a defense mechanism of B. cinerea against these naphthalentrione derivatives was analyzed. This pump could be involved in the detoxification of compounds 2, 6, and 13. On the contrary, this mechanism would not participate in the detoxification of compounds 1, 7, 9 and 12. Finally, the biotransformation of compound 7 by B. cinerea was studied. A mixture of two biotransformed products was obtained. One of them was compound 7A, which is reduced at C1 and C4, compared to compound 7. The other product of biotransformation, 7B, is oxidized at C7.

Resveratrol Preconditioning Induces Genomic and Metabolic Adaptations within the Long-Term Window of Cerebral Ischemic Tolerance Leading to Bioenergetic Efficiency

Neuroprotective agents administered post-cerebral ischemia have failed so far in the clinic to promote significant recovery. Thus, numerous efforts were redirected toward prophylactic approaches such as preconditioning as an alternative therapeutic strategy. Our laboratory has revealed a novel long-term window of cerebral ischemic tolerance mediated by resveratrol preconditioning (RPC) that lasts for 2 weeks in mice. To identify its mediators, we conducted an RNA-seq experiment on the cortex of mice 2 weeks post-RPC, which revealed 136 differentially expressed genes. The majority of genes (116/136) were downregulated upon RPC and clustered into biological processes involved in transcription, synaptic signaling, and neurotransmission. The downregulation in these processes was reminiscent of metabolic depression, an adaptation used by hibernating animals to survive severe ischemic states by downregulating energy-consuming pathways. Thus, to assess metabolism, we used a neuronal-astrocytic co-culture model and measured the cellular respiration rate at the long-term window post-RPC. Remarkably, we observed an increase in glycolysis and mitochondrial respiration efficiency upon RPC. We also observed an increase in the expression of genes involved in pyruvate uptake, TCA cycle, and oxidative phosphorylation, all of which indicated an increased reliance on energy-producing pathways. We then revealed that these nuclear and mitochondrial adaptations, which reduce the reliance on energy-consuming pathways and increase the reliance on energy-producing pathways, are epigenetically coupled through acetyl-CoA metabolism and ultimately increase baseline ATP levels. This increase in ATP would then allow the brain, a highly metabolic organ, to endure prolonged durations of energy deprivation encountered during cerebral ischemia.

Characterization of the fungitoxic activity on Botrytis cinerea of the aristolochic acids I and II

The fungitoxic effect of aristolochic acids I and II on mycelial growth and conidial germination of Botrytis cinerea was analysed. Aristolochic acid I had a higher effect on mycelial growth of B. cinerea than aristolochic acid II with IC₅₀ value of 18·7 and 57·0 μg ml^-1 , respectively. These compounds did not affect the conidia germination. Also, the effect of both compounds on DNA and plasmatic membrane integrity of B. cinerea was studied. Only aristolochic acid II was able to cause damage to the integrity of the plasmatic membrane. When the fungus was incubated with a mixture of these compounds, degradation of DNA was observed. Finally, biotransformation products were not detected in the culture broth when B. cinerea was incubated in the presence of the aristolochic acids. Studies of structural characteristics that increase the antifungal effect of compounds against B. cinerea will permit to design new molecules to control this phytopathogenic fungus. SIGNIFICANCE AND IMPACT OF THE STUDY: The fungitoxic effect on Botrytis cinerea of aristolochic acids I and II was characterized. The only structural difference among these compounds is a methoxy group at carbon 8. However, despite their structural similarity, the fungitoxic effect of aristolochic acid I was higher than the effect of aristolochic acid II. This result suggests that the methoxy group is important for the fungitoxic activity of these compounds on B. cinerea.

Synergistic Effects of Resveratrol and Pyrimethanil against Botrytis cinerea on Grape

Botrytis cinerea is the pathogen of gray mold disease affecting a wide range of plant hosts, with consequential economic losses worldwide. The increased frequency of fungicide resistance of the pathogen challenges its disease management, and thus the development of alternative control strategies are urgently required. In this study, we showed excellent synergistic interactions between resveratrol and pyrimethanil. Significant synergistic values were recorded by the two-drug combination on the suppression of mycelial growth and conidia germination of B. cinerea. The combination of resveratrol and pyrimethanil caused malformation of mycelia. Moreover, the inoculation assay was conducted on table grape and consistent synergistic suppression of the two-drug combination was found in vivo. Our findings first revealed that the combination of resveratrol and pyrimethanil has synergistic effects against resistant B. cinerea and support the potential use of resveratrol as a promising adjuvant on the control of gray mold.

LC-MS/MS Tandem Mass Spectrometry for Analysis of Phenolic Compounds and Pentacyclic Triterpenes in Antifungal Extracts of Terminalia brownii (Fresen)

Decoctions and macerations of the stem bark and wood of Terminalia brownii Fresen. are used in traditional medicine for fungal infections and as fungicides on field crops and in traditional granaries in Sudan. In addition, T. brownii water extracts are commonly used as sprays for protecting wooden houses and furniture. Therefore, using agar disc diffusion and macrodilution methods, eight extracts of various polarities from the stem wood and bark were screened for their growth-inhibitory effects against filamentous fungi commonly causing fruit, vegetable, grain and wood decay, as well as infections in the immunocompromised host. Ethyl acetate extracts of the stem wood and bark gave the best antifungal activities, with MIC values of 250 µg/mL against Nattrassia mangiferae and Fusarium verticillioides, and 500 µg/mL against Aspergillus niger and Aspergillus flavus. Aqueous extracts gave almost as potent effects as the ethyl acetate extracts against the Aspergillus and Fusarium strains, and were slightly more active than the ethyl acetate extracts against Nattrassiamangiferae. Thin layer chromatography, RP-HPLC-DAD and tandem mass spectrometry (LC-MS/MS), were employed to identify the chemical constituents in the ethyl acetate fractions of the stem bark and wood. The stem bark and wood were found to have a similar qualitative composition of polyphenols and triterpenoids, but differed quantitatively from each other. The stilbene derivatives, cis- (3) and trans- resveratrol-3-O-β-galloylglucoside (4), were identified for the first time in T. brownii. Moreover, methyl-(S)-flavogallonate (5), quercetin-7-β-O-di-glucoside (8), quercetin-7-O-galloyl-glucoside (10), naringenin-4'-methoxy-7-pyranoside (7), 5,6-dihydroxy-3',4',7-tri-methoxy flavone (12), gallagic acid dilactone (terminalin) (6), a corilagin derivative (9) and two oleanane type triterpenoids (1) and (2) were characterized. The flavonoids, a corilagin derivative and terminalin, have not been identified before in T. brownii. We reported earlier on the occurrence of methyl-S-flavogallonate and its isomer in the roots of T. brownii, but this is the first report on their occurrence in the stem wood as well. Our results justify the traditional uses of macerations and decoctions of T. brownii stem wood and bark for crop and wood protection and demonstrate that standardized extracts could have uses for the eco-friendly control of plant pathogenic fungi in African agroforestry systems. Likewise, our results justify the traditional uses of these preparations for the treatment of skin infections caused by filamentous fungi.

The Structure-Activity Relationship of Pterostilbene Against Candida albicans Biofilms

Candida albicans biofilms contribute to invasive infections and dramatic drug resistance, and anti-biofilm agents are urgently needed in the clinic. Pterostilbene (PTE) is a natural plant product with potentials to be developed as an anti-biofilm agent. In this study, we evaluated the structure-activity relationship (SAR) of PTE analogues against C. albicans biofilms. XTT (Sodium 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt) reduction assay was used to evaluate the activity of the analogues against C. albicans biofilms. Knowing that hyphal formation is essential for C. albicans biofilms, anti-hyphal assay was further carried out. By comparing a series of compounds tested in this study, we found that compounds with para-hydroxy (–OH) in partition A exhibited better activity than those with other substituents in the para position, and the double bond in partition B and meta-dimethoxy (–OCH₃) in partition C both contributed to the best activity. Consistent results were obtained by anti-hyphal assay. Collectively, para-hydroxy (–OH), double bond and meta-dimethoxy (–OCH₃) are all needed for the best activity of PTE against C. albicans biofilms.

Synthesis, Biological Evaluation, and Molecular Modeling Studies of New Oxadiazole-Stilbene Hybrids against Phytopathogenic Fungi

Natural stilbenes (especially resveratrol) play important roles in plant protection by acting as both constitutive and inducible defenses. However, their exogenous applications on crops as fungicidal agents are challenged by their oxidative degradation and limited availability. In this study, a new class of resveratrol-inspired oxadiazole-stilbene hybrids was synthesized via Wittig-Horner reaction. Bioassay results indicated that some of the compounds exhibited potent fungicidal activity against Botrytis cinerea in vitro. Among these stilbene hybrids, compounds 11 showed promising inhibitory activity with the EC₅₀ value of 144.6 μg/mL, which was superior to that of resveratrol (315.6 μg/mL). Remarkably, the considerably abnormal mycelial morphology was observed in the presence of compound 11. The inhibitory profile was further proposed by homology modeling and molecular docking studies, which showed the possible interaction of resveratrol and oxadiazole-stilbene hybrids with the cytochrome P450-dependent sterol 14α-demethylase from B. cinerea (BcCYP51) for the first time. Taken together, these results would provide new insights into the fungicidal mechanism of stilbenes, as well as an important clue for biology-oriented synthesis of stilbene hybrids with improved bioactivity against plant pathogenic fungi in crop protection.

Pterostilbene Is a Potential Candidate for Control of Blackleg in Canola

Two stilbenes, resveratrol and pterostilbene, exhibit antifungal activity against Leptosphaeria maculans, the fungal pathogen responsible for blackleg (stem canker) in canola (Brassica napus). In vitro studies on the effect of these stilbenes on L. maculans mycelial growth and conidia germination showed that pterostilbene is a potent fungicide and sporicide, but resveratrol only exerted minor inhibition on L. maculans. Cell viability of hyphae cultures was markedly reduced by pterostilbene and SYTOX green staining showed that cell membrane integrity was compromised. We demonstrate that pterostilbene exerts fungicidal activity across 10 different L. maculans isolates and the compound confers protection to the blackleg-susceptible canola cv. Westar seedlings. The potential of pterostilbene as a control agent against blackleg in canola is discussed.

PHYSIOLOGICAL EFFECTS OF RESVERATROL AND COUMARIC ACID ON TWO MAJOR GROUNDNUT PESTS AND THEIR EGG PARASITOID BEHAVIOR

Groundnut, Arachis hypogea L., is one of the plant species that synthesizes phenolic compounds, resveratrol and coumaric acid. They are induced as a defense strategy in plant in response to feeding lepidopterans. The present study investigated the role of resveratrol and coumaric acid in producing antiherbivore effects as a direct defense against two major groundnut pests, Spodoptera litura F. and Amsacta albistriga W., and in indirect defense by attracting the egg parasitoid Trichogramma chilonis Ishii under laboratory conditions. The phenolic compounds deterred the feeding of both pests and caused reduction in the larval weights in a dose-dependent manner in leaf disk bioassays. Antioxidant mechanisms of larvae fed with these phenols were measured by estimating the activities of superoxide dismutase (SOD), ascorbate peroxidase (APOX), and catalase (CAT). Enzyme activities increased significantly in experimental larvae, more so in resveratrol-treated than in coumaric acid treated larvae. Feeding larvae with resveratrol and coumaric acid resulted in enhanced activities of detoxifying enzymes, carboxyl esterase (EST), and glutathione-S-transferase (GST) in the midgut tissues of both species, indicating the toxic nature of these compounds. Trichogramma chilonis was more attracted toward coumaric acid treatments in Y-olfactometer tests than to resveratrol. This study contributes to the understanding of the roles of resveratrol and coumaric acid in direct as well as indirect defense, we infer a possible utilization of these compounds in alternate measures of groundnut pest control in future.

Synthesis and biological evaluation of novel fluorine-containing stilbene derivatives as fungicidal agents against phytopathogenic fungi

The rising development of resistance to conventional fungicides is driving the search for new alternative candidates to control plant diseases. In this study, a series of new fluorine-containing stilbene derivatives was synthesized on the basis of our previous quantitative structure-activity relationship analysis results. Bioassays in vivo revealed that the title compounds exhibited potent fungicidal activities against phytopathogenic fungi (Colletotrichum lagenarium and Pseudoperonospora cubensis) from cucumber plants. In comparison to the previous results, the introduction of a fluorine moiety showed improved activities of some compounds against those fungi. Notably, compound 9 exhibited a control efficacy against C. lagenarium (83.4 ± 1.3%) comparable to that of commercial fungicide (82.7 ± 1.7%). For further understanding the possible mode of action of the stilbene against C. lagenarium, the effects on hyphal morphology, electrolyte leakage, and respiration of mycelial cell suspension were studied. Microscopic observation showed considerably deformed mycelial morphology. The conductivity of mycelial suspension increased in the presence of compound 9, whereas no significantly inhibitory effect on respiration was observed. Taken together, the fungicidal mechanism of this stilbene is associated with its membrane disruption effect, resulting in increased membrane permeability. These results provide important clues for mechanistic study and derivatization of stilbenes as alternative sources of fungicidal agents for plant disease control.

Alternative oxidase inhibitors as antiparasitic agents against scuticociliatosis

Philasterides dicentrarchi causes a severe disease in turbot, and at present there are no drugs available to treat infected fish. We have previously demonstrated that, in addition to the classical respiratory pathway, P. dicentrarchi possesses an alternative mitochondrial respiratory pathway that is cyanide-insensitive and salicylhydroxamic acid (SHAM)-sensitive. In this study, we found that during the initial phase of growth in normoxia, ciliate respiration is sensitive to the natural polyphenol resveratrol (RESV) and to Antimycin A (AMA). However, under hypoxic conditions, the parasite utilizes AMA-insensitive respiration, which is completely inhibited by RESV and by the antioxidant propyl gallate (PG), an alternative oxidase (AOX) inhibitor. PG caused significantly dose-dependent inhibition of the in vitro growth of the parasite under normoxia and hypoxia and an over-expression of heat shock proteins of the Hsp70 subfamily. RESV and PG may affect the protective role of the AOX against mitochondrial oxidative stress, leading to an impaired mitochondrial membrane potential and mitochondrial dysfunction, which the parasite attempts to neutralize by increasing the expression of Hsp70. In view of the antiparasitic effects induced by AOX inhibitors and the absence of AOX in their host, this enzyme constitutes a potential target for the development of new drugs against scuticociliatosis.