Marine-natural-products for biocides development: first discovery of meridianin alkaloids as antiviral and anti-phytopathogenic-fungus agents

Design, Synthesis, and Biological Evaluation of 2-Arylaminopyrimidine Derivatives as Dual Cathepsin L and JAK Inhibitors for the Treatment of Acute Lung Injury

Acute lung injury (ALI) is a disease characterized by pulmonary inflammation, blood barrier functional disorder, and hypoxemia. Herein, a series of 2-aminopyrimidine derivatives were synthesized. Most of them exhibited inhibitory effects on inflammatory cytokines IL-6 and IL-8 in human bronchial epithelial (HBE) cells at a concentration of 5 μM without significant cytotoxicity. Compound A8 displayed an excellent anti-inflammatory activity, achieving inhibition rates of 83% for IL-6 and 85% for IL-8. Besides, A8 has a strong binding affinity to CTSL and a good inhibitory activity on JAKs. Western blot analysis indicated that compound A8 strongly blocked the maturation of CTSL and the phosphorylation of p-38, p-65, and STATs, thereby repressing the activation of the MAPK, NF-κB, and JAK/STAT signaling pathway. Moreover, animal experiments showed that A8 played a protective and therapeutic role in ALI in mice, validating its potential as a treatment for ALI.

Discovery of Novel Chiral Indole Derivatives Containing the Oxazoline Moiety as Potential Antiviral Agents for Plants

Potato virus Y (PVY) is an important plant virus that has spread worldwide, causing significant economic losses. To search for novel structures as potent antiviral agents, a series of chiral indole derivatives containing oxazoline moieties were designed and synthesized and their anti-PVY activities were evaluated. Biological activity tests demonstrated that many chiral compounds exhibited promising anti-PVY activities and that their absolute configurations exhibited obvious distinctions in antiviral bioactivities. Notably, compound (S)-4v displayed excellent curative and protective efficacy against PVY, with EC50 values of 328.6 and 256.1 μg/mL, respectively, which were superior to those of commercial virucide ningnanmycin (NNM, 437.4 and 397.4 μg/mL, respectively). The preliminary antiviral mechanism was investigated to determine the difference in antiviral activity between the two enantiomers of 4v chiral compounds. Molecular docking indicated a stronger binding affinity between the coating proteins of PVY (PVY-CP) and (S)-4v (-6.5 kcal/mol) compared to (R)-4v (-6.2 kcal/mol). Additionally, compound (S)-4v can increase the chlorophyll content and defense-related enzyme activities more effectively than its enantiomer. Therefore, this study provides an important basis for the development of chiral indole derivatives containing oxazoline moieties as novel agricultural chemicals.

Protecting-Group-Free Synthesis of Meridianin A-G and Derivatives and Its Antibiofilm Evaluation

Herein, a protecting-group-free protocol was developed to realize a time and step economy diversification of the Meridianin alkaloid. A broad range of substituents are tolerated to deliver the products in moderate to high yields, and the first synthesis of Meridianin B was achieved. The simplicity of this protocol enables the rapid construction of a Meridianin derivative library for antibiofilm evaluation. Preliminary results reveal that Meridianin derivatives were capable of inhibiting the Acinetobacter baumannii biofilm and lowering the antibiotic MIC synergistically.

Allicin-inspired disulfide derivatives containing quinazolin-4(3H)-one as a bacteriostat against Xanthomonas oryzae pv. oryzae

BACKGROUND

Plant bacterial diseases have seriously affected the yield and quality of crops, among which rice bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae has seriously affected the yield of rice. As plant-pathogenic bacteria gradually become resistant to existing bactericides, it is necessary to find effective bactericides with novel structures.

RESULTS

Herein, a series of compounds containing quinazolin-4(3H)-one and disulfide moieties were designed and synthesized using a facile synthetic method. The bioassay results revealed that most target compounds possessed noticeable antibacterial activity against Xanthomonas oryzae pv. oryzae. Particularly, compound 2-(butyldisulfanyl) quinazolin-4(3H)-one (1) exhibited remarkable antibacterial activity with the half effective concentration (EC₅₀ ) of 0.52 μg mL^-1 . Additionally, compound 1 was confirmed to inhibit the growth of the bacteria, change the bacterial morphology, and increase the level of reactive oxygen species. Proteomics, and RT-qPCR analysis results indicated that compound 1 could downregulate the expression of Pil-Chp histidine kinase chpA encoded by the pilL gene, and the potting experiments proved that compound 1 exhibits significant protective activity against BLB.

CONCLUSIONS

Compound 1 may weaken the pathogenicity of Xanthomonas oryzae pv. oryzae by inhibiting the bacterial growth and blocking the pili-mediated twitching motility without inducing the bacterial apoptosis. This study indicates that such derivatives could be a promising scaffold to develop a bacteriostat to control BLB. © 2022 Society of Chemical Industry.

Recent Achievements in Antiviral Agent Development for Plant Protection

Plant virus disease is the second most prevalent plant diseases and can cause extensive loss in global agricultural economy. Extensive work has been carried out on the development of novel antiplant virus agents for preventing and treating plant virus diseases. In this review, we summarize the achievements of the research and development of new antiviral agents in the recent five years and provide our own perspective on the future development in this highly active research field.

A Survey on the Synthesis of Variolins, Meridianins, and Meriolins-Naturally Occurring Marine (aza)Indole Alkaloids and Their Semisynthetic Derivatives

Marine natural products are a source of essential significance due to a plethora of highly diverse biological properties. The naturally occurring (aza)indole alkaloids variolin B (1), meridianins (2), and their synthetic hybrids meriolins (3) exhibit potent kinase inhibitory activities and have aroused considerable interest in the past two decades. Therefore, the immense demand for versatile synthetic accesses to these structures has considerably increased. This review surveys the synthetic pathways to these naturally occurring alkaloids and their semisynthetic derivatives.

A Review: Meridianins and Meridianins Derivatives

Meridianins are a family of indole alkaloids derived from Antarctic tunicates with extensive pharmacological activities. A series of meridianin derivatives had been synthesized by drug researchers. This article reviews the extraction and purification methods, biological activities and pharmacological applications, pharmacokinetic characters and chemical synthesis of meridianins and their derivatives. And prospects on discovering new bioactivities of meridianins and optimizing their structure for the improvement of the ADMET properties are provided.

Phenyl Ethers from the Marine-Derived Fungus Aspergillus tabacinus and Their Antimicrobial Activity Against Plant Pathogenic Fungi and Bacteria

Marine fungi produce various secondary metabolites with unique chemical structures and diverse biological activities. In the continuing search for new antifungal agents from fungi isolated from marine environments, the culture filtrate of a fungus Aspergillus tabacinus SFC20160407-M11 exhibited the potential to control plant diseases caused by fungi. From the culture filtrate of A. tabacinus SFC20160407-M11, a total of seven compounds were isolated and identified by activity-guided column chromatography and spectroscopic analysis: violaceol I (1), violaceol II (2), diorcinol (3), versinol (4), orcinol (5), orsellinic acid (6), and sydowiol C (7). Based on in vitro bioassays against 17 plant pathogenic fungi and bacteria, violaceols and diorcinol (1-3) showed a broad spectrum of antimicrobial activity with minimum inhibitory concentration values in the range of 6.3-200 μg mL^-1. These compounds also effectively reduced the development of rice blast, tomato late blight, and pepper anthracnose caused by plant pathogenic fungi in a dose-dependent manner. Our results suggest that A. tabacinus SFC20160407-M11 and its phenyl ether compounds could be used for developing new antimicrobial agents to protect crops from plant pathogens.

Recent Research Progress: Discovery of Anti-Plant Virus Agents Based on Natural Scaffold

Plant virus diseases, also known as “plant cancers”, cause serious harm to the agriculture of the world and huge economic losses every year. Antiviral agents are one of the most effective ways to control plant virus diseases. Ningnanmycin is currently the most successful anti-plant virus agent, but its field control effect is not ideal due to its instability. In recent years, great progress has been made in the research and development of antiviral agents, the mainstream research direction is to obtain antiviral agents or lead compounds based on structural modification of natural products. However, no antiviral agent has been able to completely inhibit plant viruses. Therefore, the development of highly effective antiviral agents still faces enormous challenges. Therefore, we reviewed the recent research progress of anti-plant virus agents based on natural products in the past decade, and discussed their structure-activity relationship (SAR) and mechanism of action. It is hoped that this review can provide new inspiration for the discovery and mechanism of action of novel antiviral agents.

Role of Indole Derivatives in Agrochemistry: Synthesis and Future Insights

Abstract:

Heterocycles constitute a wider class of organic compounds which contribute significantly in every facet of pure and applied chemistry. Indole, one of the bicyclic heterocyclic compounds containing nitrogen atom, witnessed unparalleled biological activity such as antiviral, antibacterial, anticancer, anti-depressant and antifungal activities. Different biological activities exhibited by indole derivatives provide the impulsion to explore its activity against anti-phytopathogenic microbes to save the plants from pests and disease, as food security will once again become a rigid demand. This review mainly focuses on various methods related to the synthesis of indole derivatives and its role in agriculture.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Design, Synthesis and Structure-Activity Relationship Studies of Meridianin Derivatives as Novel JAK/STAT3 Signaling Inhibitors

Hyperactivation of Janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) signaling is an attractive therapeutic target for tumor therapy. Herein, forty-eight novel meridianin derivatives were designed and synthesized, and their antitumor activity was evaluated in vitro both for activity optimization and structure–activity relationship (SAR) study. The results indicated that most derivatives exhibited significantly improved antitumor activity, especially for compound 6e. The compound 6e contains an isothiouronium linked by an alkyl chain consisting of six carbon atoms with IC₅₀ ranging from 1.11 to 2.80 μM on various cancer cell lines. Consistently, the 6e dose dependently induced the apoptosis of A549 and DU145 cells, in which STAT3 is constitutively active. Western blotting assays indicated that the phosphorylation levels of JAK1, JAK2 and STAT3 were inhibited by 6e at 5 μM without significant change in the total STAT3 level. Moreover, 6e also suppressed the expression of STAT3 downstream genes, including c-Myc, Cyclin D1 and Bcl-XL at 10 μM. An additional in vivo study revealed that 6e at the dose of 10 mg/kg could potently inhibit the DU145 xenograft tumor without obvious body weight loss. These results clearly indicate that 6e could be a potential antitumor agent by targeting the JAK/STAT3 signaling pathway.

Design, Synthesis, and Bioactivities of Phthalide and Coumarin Derivatives Based on the Biosynthesis and Structure Simplification of Gossypol

Because gossypol and hemigossypol show antiviral activity but are structurally complex, we designed and synthesized a series of structurally simpler phthalide and coumarin derivatives. The phthalide derivatives were synthesized by opening the naphthalene ring of hemigossypol, and the coumarin derivatives were synthesized by ring-opening reactions of the phthalide derivatives with the goal of investigating the effect of the lactone ring size on bioactivity. The bioassay results showed that the two series of target compounds possessed moderate to good activities against tobacco mosaic virus, One of the compounds showed in vivo inactivation, curative, and protection activities of 50 ± 1, 53 ± 3, and 48 ± 2% at 500 mg/L, values which are higher than those of gossypol (32 ± 1, 35 ± 1, 29 ± 1%, respectively) and comparable to those of hemigossypol (55 ± 1, 49 ± 1, and 48 ± 1%, respectively) and the commercial antiviral agent ningnanmycin (56 ± 2, 54 ± 1, 58 ± 1%) at the same dose. Thus, this compound is a promising candidate for the development of new anti-plant-virus agents. In addition, most of the synthesized compounds showed broad-spectrum activity when tested against 14 kinds of phytopathogenic fungi and showed selectivity against Sclerotinia sclerotiorum, Physalospora piricola, and Rhizoctonia cerealis. Moreover, some of the compounds exhibited activity against Plutella xylostella larvae; the two most active compounds exhibited larvicidal activities (LC₅₀) of 4.10 and 5.47 mg/L, respectively. Further studies showed that these compounds also exhibited insecticidal activities against Mythimna separata, Helicoverpa armigera, and Pyrausta nubilalis larvae.

Identification of Carbazole Alkaloid Derivatives with Acylhydrazone as Novel Anti-TMV Agents with the Guidance of a Digital Fluorescence Visual Screening

Difficulty in preventing crops from plant viruses urges to discover novel efficient antiviral chemicals, which is sped up by precise screening methods. Fluorescence-based methods have recently been applied as innovative and rapid tools for visually monitoring the replication of viruses and screening of antivirals, whereas the quantification of fluorescence signals mainly depends on manually calculating the fluorescent spots, which is time-consuming and imprecise. In the present work, the fluorescence spots were automatically identified, and the fluorescence area was directly quantified by a program developed in our group, which avoided subjective errors from the operators. We further employed this digital and visual screening assay to identify antivirals using the tobacco mosaic virus-green fluorescence protein (TMV-GFP) construct, in which the expression of GFP intuitively reflected the efficacy of antivirals. The accuracy of this assay was validated by quantifying the activities of the commercial antiviral inhibitors ribavirin and ningnanmycin and then was applied to evaluate the subtle activity differences of a series of newly synthesized carbazole and β-carboline alkaloid derivatives. Among them, compounds 5 (76%) and 11 (63%) exhibited anti-TMV activities comparable to that of ningnanmycin (65%) at 50 μM, and they delayed the multiplication of TMV in the early stage of infection without phytotoxicity. Taken together, these findings demonstrated that the digital and visual TMV-GFP screening method was competent to test the antiviral activities of compounds with subtle modifications and facilitated the discovery of novel antivirals.

Evolving challenges and strategies for fungal control in the food supply chain

Fungi that spoil foods or infect crops can have major socioeconomic impacts, posing threats to food security. The strategies needed to manage these fungi are evolving, given the growing incidence of fungicide resistance, tightening regulations of chemicals use and market trends imposing new food-preservation challenges. For example, alternative methods for crop protection such as RNA-based fungicides, biocontrol, or stimulation of natural plant defences may lessen concerns like environmental toxicity of chemical fungicides. There is renewed focus on natural product preservatives and fungicides, which can bypass regulations for 'clean label' food products. These require investment to find effective, safe activities within complex mixtures such as plant extracts. Alternatively, physical measures may be one key for fungal control, such as polymer materials which passively resist attachment and colonization by fungi. Reducing or replacing traditional chlorine treatments (e.g. of post-harvest produce) is desirable to limit formation of disinfection by-products. In addition, the current growth in lower sugar food products can alter metabolic routing of carbon utilization in spoilage yeasts, with implications for efficacy of food preservatives acting via metabolism. The use of preservative or fungicide combinations, while involving more than one chemical, can reduce total chemicals usage where these act synergistically. Such approaches might also help target different subpopulations within heteroresistant fungal populations. These approaches are discussed in the context of current challenges for food preservation, focussing on pre-harvest fungal control, fresh produce and stored food preservation. Several strategies show growing potential for mitigating or reversing the risks posed by fungi in the food supply chain.

Discovery of novel indole derivatives containing dithioacetal as potential antiviral agents for plants

Thirty unreported indole derivatives containing dithioacetal moiety were synthesized and evaluated for anti-plant viral activity. Bioassay results displayed that some of the target compounds showed better activities against tobacco mosaic virus (TMV) than the commercial Ribavirin in vivo. In particular, anti-TMV curative, protective and inactivating activity of 4p were 55.1, 57.2, and 80.3%, respectively, and EC₅₀ value for inactivating activity was 88.5 μg/mL. The observation of transmission electron microscope showed that 4p may have a certain destructive effect on TMV particles. To further study, microscale thermophoresis analysis result also demonstrated that 4p powerfully interacted with TMV coat protein in vitro. Hence, this study provides a strong evidence suporting that indole derivatives might be applied as new antiviral agents.