Natural products as sources of new fungicides (V): Design and synthesis of acetophenone derivatives against phytopathogenic fungi in vitro and in vivo

Natural Alkaloid Waltherione F-Derived Hydrazide Compounds Evaluated in an Agricultural Fungicidal Field

In this project, quinoline and quinolone-containing hydrazide compounds were designed and synthesized by introducing a bioactive hydrazide group into the skeleton of waltherione F. The fungicidal activity revealed that some hydrazide compounds exhibited excellent and broad-spectrum fungicidal activity; especially, compounds E8, E12, and E16 showed more than 90% or even 100% inhibition rates against most pathogens at 50 μg·mL-1. The fungicidal mechanism indicated that compound E8 may affect the normal function of the plasma membrane, further generating changes in the morphology and subcellular structure of mycelia. Simultaneously, Fusarium graminearum may resist the E8-treated stress through the metabolic pathways related to l-glutamate, l-glutamine, and glutathione. Finally, the effect of compound E8 on wheat seedling's growth and the toxicity to zebrafish were accomplished. These results will provide important guidance to discover novel fungicidal lead compounds and explore new targets, which are effective ways to alleviate the increasingly severe drug resistance.

Ru(II)-Catalyzed Weakly Coordinating Carbonyl-Assisted Dialkynylation of (Hetero)Aryl Ketones

Functionalized aryl(heteroaryl) ketones are present in many natural products as key structural components and serve as basic synthetic building blocks for various organic transformation reactions. Therefore, the development of an effective and sustainable route for making these classes of compounds remains challenging yet highly desirable. Herein, we report a simple and efficient catalytic system for dialkynylation of aromatic/heteroaromatic ketones via a double C-H bond activation in the presence of less expensive ruthenium(II)-salt as a catalyst using the weakly and native carbonyl group as the desired directing group. The developed protocol is highly compatible, tolerant, and sustainable toward various functional groups. The synthetic utility of the developed protocol has been demonstrated through the scale-up synthesis and functional group transformation. Control experiments support the involvement of the base-assisted internal electrophilic substitution (BIES) reaction pathway.

Antifungal Activity of 2-Allylphenol Derivatives on the Botrytis cinerea Strain: Assessment of Possible Action Mechanism

Botrytis cinerea is a phytopathogenic fungus that causes serious damage to the agricultural industry by infecting various important crops. 2-allylphenol has been used in China as a fungicide for more than a decade, and it has been shown that is a respiration inhibitor. A series of derivatives of 2-allylphenol were synthesized and their activity against B. cinerea was evaluated by measuring mycelial growth inhibition. Results indicate that small changes in the chemical structure or the addition of substituent groups in the aromatic ring induce important variations in activity. For example, changing the hydroxyl group by methoxy or acetyl groups produces dramatic increases in mycelial growth inhibition, i.e., the IC50 value of 2-allylphenol decreases from 68 to 2 and 1 μg mL−1. In addition, it was found that the most active derivatives induce the inhibition of Bcaox expression in the early stages of B. cinerea conidia germination. This gene is associated with the activation of the alternative oxidase enzyme (AOX), which allows fungus respiration to continue in the presence of respiratory inhibitors. Thus, it seems that 2-allylphenol derivatives can inhibit the normal and alternative respiratory pathway of B. cinerea. Therefore, we believe that these compounds are a very attractive platform for the development of antifungal agents against B. cinerea.

Design, synthesis, and bioactivity of ferulic acid derivatives containing an β-amino alcohol

Background

Plant diseases caused by viruses and bacteria cause huge economic losses due to the lack of effective control agents. New potential pesticides can be discovered through biomimetic synthesis and structural modification of natural products. A series of ferulic acid derivatives containing an β-amino alcohol were designed and synthesized, and their biological activities were evaluated.

Result

Bioassays results showed that the EC₅₀ values of compound D24 against Xanthomonas oryzae pv. oryzae (Xoo) was 14.5 μg/mL, which was better than that of bismerthiazol (BT, EC₅₀ = 16.2 μg/mL) and thiodiazole copper (TC, EC₅₀ = 44.5 μg/mL). The in vivo curative and protective activities of compound D24 against Xoo were 50.5% and 50.1%, respectively. The inactivation activities of compounds D2, D3 and D4 against tobacco mosaic virus (TMV) at 500 μg/mL were 89.1, 93.7 and 89.5%, respectively, superior to ningnanmycin (93.2%) and ribavirin (73.5%). In particular, the EC₅₀ value of compound D3 was 38.1 μg/mL, and its molecular docking results showed that compound D3 had a strong affinity for TMV-CP with a binding energy of − 7.54 kcal/mol, which was superior to that of ningnanmycin (− 6.88 kcal /mol).

Conclusions

The preliminary mechanism research results indicated that compound D3 may disrupt the three-dimensional structure of the TMV coat protein, making TMV particles unable to self-assemble, which may provide potential lead compounds for the discovery of novel plant antiviral agents.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13065-022-00828-8.

Ten Years of Glory in the α-Functionalizations of Acetophenones: Progress Through Kornblum Oxidation and C-H Functionalization

This review article focuses on the α-functionalization of acetophenones involving Kornblum oxidation and C-H functionalizations. Although various other strategies, such as classical approaches, enamine approaches and umpolung strategy are also known for this functionalization, here we discuss mainly the Kornblum oxidation approach and C-H functionalization strategy as they have advantages over the others. In Kornblum oxidation, the reaction uses iodine and dimethylsulfoxide and proceeds through the formation of arylglyoxal as the key intermediate. In C-H functionalization, the reaction requires metal, or metal-free catalyst, and generates radical intermediate in most cases. α-Functionalization of acetophenones is very important because of their huge applications in the synthesis of various natural products and pharmaceuticals and, therefore, a number of research articles have been published in this area. However, no review articles are available so far. In this article, we present a succinct discussion of various important and novel reactions, along with their mechanisms, published since 2012 to date. We believe that this first review article in this field will give readers one-stop information on this topic and encourage further intriguing work in this area.

The Antifungal Mechanism of Isoxanthohumol from Humulus lupulus Linn

Humulus lupulus Linn. is a traditional medicinal and edible plant with several biological properties. The aims of this work were: (1) to evaluate the in vitro antifungal activity of H. lupulus ethanolic extract; (2) to study the in vitro and in vivo antifungal activity of isoxanthohumol, an isoprene flavonoid from H. lupulus, against Botrytis cinerea; and (3) to explore the antifungal mechanism of isoxanthohumol on B. cinerea. The present data revealed that the ethanolic extract of H. lupulus exhibited moderate antifungal activity against the five tested phytopathogenic fungi in vitro, and isoxanthohumol showed highly significant antifungal activity against B. cinerea, with an EC₅₀ value of 4.32 µg/mL. Meanwhile, it exhibited moderate to excellent protective and curative efficacies in vivo. The results of morphologic observation, RNA-seq, and physiological indicators revealed that the antifungal mechanism of isoxanthohumol is mainly related to metabolism; it affected the carbohydrate metabolic process, destroyed the tricarboxylic acid (TCA) cycle, and hindered the generation of ATP by inhibiting respiration. Further studies indicated that isoxanthohumol caused membrane lipid peroxidation, thus accelerating the death of B. cinerea. This study demonstrates that isoxanthohumol can be used as a potential botanical fungicide for the management of phytopathogenic fungi.

Characterisation, pathogenicity and hydrolytic enzyme profiling of selected Fusarium species and their inhibition by novel coumarins

Three Fusarium species isolated locally were characterised by the amplification of their rDNA ITS region, host specificity, and hydrolytic enzyme production. The strains were identified as Fusarium pseudoanthophilum, which is being reported for the first time in South Africa, as well as F. foetens and F. fujikuroi. All the three strains were capable of infecting vegetables such as tomatoes, bell and cayenne peppers, belonging to the Solanaceae family. The Fusarium strains also showed significant production of cell wall degrading enzymes in vitro, such as amylase, cellulase, xylanase, and polygalacturonase, thus highlighting the possibilities of these enzymes as pathogenic factors. Subsequently, the strains were discovered to be susceptible to three halogenated coumarins. The most effective of the tested coumarins, 6-bromo3-2,2-dibromoacetyl-2H-chromen-2-one, showed MIC values of 0.125, 0.0625 and 0.125 mg/ml against F. foetens, F. pseudoanthophilum and F. fujikuroi, respectively. The antifungal potentials of the halogenated coumarins were confirmed in silico through PASS analysis, toxicity prediction and docking studies. Findings from this study demonstrate the use of these coumarins as potential control agents against the Fusarium species and other pathogenic fungi in general.

Preparation of Matrinic/Oxymatrinic Amide Derivatives as Insecticidal/Acaricidal Agents and Study on the Mechanisms of Action against Tetranychus cinnabarinus

In continuation of our program to develop natural-product-based pesticidal candidates, matrinic/oxymatrinic amides were obtained through structural optimization of matrine. N'-(4-Fluoro)phenyl-N-(4-bromo)phenylsulfonyloxymatrinic amide (IIm) showed potent insecticidal activity against Mythimna separata. N-(Un)substituted phenylsulfonylmatrinic acids (3a-c) exhibited promising acaricidal activity against Tetranychus cinnabarinus. By qRT-PCR analysis of nAChR subunits and AChE genes and determination of AChE activity of (un)treated T. cinnabarinus, it suggested that the open lactam ring of matrine and carboxyl group and (4-methyl)phenylsulfonyl of N-(4-methyl)phenylsulfonylmatrinic acid (3b) were necessary for action with α2, α4, α5, and β3 nAChR subunits; compound 3b was an inhibitor of AChE in T. cinnabarinus, and AChE was one possible target of action in T. cinnabarinus against 3b; and compound 3b may be an antagonist of nAChR and AChE in T. cinnabarinus.

Cynanchum bungei Decne and its two related species for "Baishouwu": A review on traditional uses, phytochemistry, and pharmacological activities

ETHNOPHARMACOLOGICAL RELEVANCE

Cynanchum bungei Decne. (CB) (Asclepiadaceae) and its two related species Cynanchum auriculatum Royle ex Wight. (CA) and Cynanchum wilfordii (Maxim.) Hemsl. (CW) are well known Chinese herbal medicines known by the name Baishouwu. Among them, CB has long been used for nourishing the kidney and liver, strengthening the bones and muscles, and regulating stomachache. However, to date, no comprehensive review on Baishouwu has been published.

AIM OF THE REVIEW

This review aims to provide a comprehensive summary on traditional uses, phytochemistry, pharmacology, and toxicology of the three herbal components of Baishouwu with the ultimate objective of providing a guide for future scientific and therapeutic potential use of Baishouwu.

MATERIAL AND METHODS

A literature search was undertaken on CB, CA and CW by analyzing the information from scientific databases (SciFinder, Pubmed, Elsevier, Google Scholar, Web of Science, and Baidu Scholar). Information was also gathered from local classic herbal literatures and conference papers on ethnopharmacology and the information provided in this review has been obtained from peer-reviewed papers.

RESULTS

Comparative analysis of literature search indicate that ethnopharmacological use of CB was recorded in China, however, CA and CW have been used in China, Korea and Japan. To date, 151 chemical compounds have been isolated from these species, and the major chemical constituents have been revealed to be acetophenones, C₂₁-steroids, terpenoids, and alkaloids. These compounds and extracts have been proven to exhibit significant pharmacological activities, including anti-tumor, anti-inflammatory, immunomodulatory, hypolipidemic, anti-obesity, hepatoprotective, antifungal, antiviral, anti-depressant, vasodilating and estrogenic activities.

CONCLUSIONS

CB, CA and CW collectively known as Baishouwu are valuable medicinal herbs with multiple pharmacological activities. The traditional use for nourishing liver is closely associated with the hepatoprotective activity. The available literature performs that various of the activity of Baishouwu can be attributed to acetophenones and C₂₁-steroids. It is high time that more efforts should be focused on the underlying mechanisms of their beneficial bioactivities and the structure activity relationship of the constituents, as well as their potential synergistic and antagonistic effects. The proper toxicology evaluation is crucial to guarantee the safety, efficacy, and eligibility for medical use. Further research on the comprehensive evaluation of medicinal quality and the understanding of multi-target network pharmacology of Baishouwu is in great request.

Benzonate derivatives of acetophenone as potent α-glucosidase inhibitors: synthesis, structure-activity relationship and mechanism

In this article, 23 compounds (6 and 7a–7v) were prepared and evaluated for their in vitro α-glucosidase inhibitory activity. The compounds 7d, 7f, 7i, 7n, 7o, 7r, 7s, 7u, and 7v displayed the α-glucosidase inhibition activity with IC₅₀ values ranging from 1.68 to 7.88 µM. Among all tested compounds, 7u was found to be the most efficient, being 32-fold more active than the standard drug acarbose, which significantly attenuated postprandial blood glucose in mice. In addition, the compound 7u also induced the fluorescence quenching and conformational changes of enzyme, by forming α-glucosidase–7u complex in a mixed inhibition type. The thermodynamic constants recognised the interaction between 7u and α-glucosidase and was an enthalpy-driven spontaneous exothermic reaction. The synchronous fluorescence and CD spectra also indicate that the compound 7u changed the enzyme conformation. The findings identify the binding interactions between new ligands and α-glucosidase and reveal the compound 7u as a potent α-glucosidase inhibitor.

Promising Fungicides from Allelochemicals: Synthesis of Umbelliferone Derivatives and Their Structure⁻Activity Relationships

Umbelliferone was discovered to be an important allelochemical in our previous study, but the contribution of its activity and structure has not yet been revealed. In this study, a series of analogues were synthesized to determine the skeleton of umbelliferone and examine its fungicidal activity. Furthermore, targeted modifications were conducted with three plant parasitic fungi to examine the lead compounds. Among those tested, compounds 2f and 10 were found to show excellent antifungal activity with an inhibitory rate over 80% at 100 ug/mL. The study proves that umbelliferone can be a promising skeleton for fungicides discovery. In addition, the primary structure–activity relationship provides a good guidance for the discovery of novel fungicides based on natural products in the future.