Synthesis and Antifungal Activity of Derivatives of the Natural Product Griseofulvin against Phytopathogenic Fungi

An Unusual Meroterpenoid and Two New Steroids From Fungus Penicillium fellutanum and Their Bioactivities

An unusual clathrate-type meroterpenoid isoatlantinone A (1), two new steroids acrocalysterols E (2) and F (3), together with fifteen known compounds (4-18) were separated from a plant-associated fungus Penicillium fellutanum. Their structures and absolute configurations were established based on spectroscopic data (nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry), electronic circular dichroism and modified Mosher's method. Notably, compound 1 represents an unusual highly oxygenated meroterpenoid derivative with a unique caged bioxatetracyclo-[6.3.2.01,6.01,12]-tridecane ring system. All compounds were assessed in vitro for antifungal and cytotoxic activities. Intriguingly, compound 16 exhibited potent antifungal activity against Fusarium culmorum with a minimum inhibitory concentration value of 50 µM, similar to the positive control carbendazim. Furthermore, compound 3 displayed potent cytotoxic effects on HCC-1806, with a half-maximal inhibitory concentration (IC50) value of 18.15 ± 1.05 µM, and compound 6 exhibited remarkable cytotoxic activities on RKO, with an IC50 value of 11.61 ± 0.19 µM. Thus, strain P. fellutanum represents a novel resource of these bioactive compounds to be exploited.

The Significance of Mono- and Dual-Effective Agents in the Development of New Antifungal Strategies

Invasive fungal infections (IFIs) pose significant challenges in clinical settings, particularly due to their high morbidity and mortality rates. The rising incidence of these infections, coupled with increasing antifungal resistance, underscores the urgent need for novel therapeutic strategies. Current antifungal drugs target the fungal cell membrane, cell wall, or intracellular components, but resistance mechanisms such as altered drug-target interactions, enhanced efflux, and adaptive cellular responses have diminished their efficacy. Recent research has highlighted the potential of dual inhibitors that simultaneously target multiple pathways or enzymes involved in fungal growth and survival. Combining pharmacophores, such as lanosterol 14α-demethylase (CYP51), heat shock protein 90 (HSP90), histone deacetylase (HDAC), and squalene epoxidase (SE) inhibitors, has led to the development of compounds with enhanced antifungal activity and reduced resistance. This dual-target approach, along with novel chemical scaffolds, not only represents a promising strategy for combating antifungal resistance but is also being utilized in the development of anticancer agents. This review explores the development of new antifungal agents that employ mono-, dual-, or multi-target strategies to combat IFIs. We discuss emerging antifungal targets, resistance mechanisms, and innovative therapeutic approaches that offer hope in managing these challenging infections.

Design, synthesis, antifungal, and antibacterial evaluation of ferulic acid derivatives bearing amide moiety

Natural compounds' derivatives as lead structures could effectively solve plant disease problems. In this article, amide compounds and amide ester compounds were synthetized through ferulic acid as the parent nucleus structure, and their biological activities in vitro and in vivo were evaluated. Compound 1q was screened out as the one with the best activity performance toward Xanthomonas axonopodis pv. citri (Xac), which displayed the inhibition rate of 100% and the EC50 as low as 4.56 μg/mL. The results of in vivo experiments on citrus leaves infected with Xac showed that compound 1q had a protective efficacy of 60.98% and a curative efficacy of 26.56%. The mechanism of action as well as molecular docking was previously studied using extracellular polysaccharide (EPS) content, bacterial membrane permeability, and scanning electron microscopy (SEM) observations. Experimental results show that compound 1q can become an antibacterial agent for preventing and managing plant diseases.

Discovery of New Antifungal Polyketides Cladrioides A-N against Phytopathogenic Fungi from Cladosporium cladosporioides LD-8

During the search for natural fungicides, 14 new australifungin analogues cladrioides A-S (1-14) and two known ones (15 and 16) were obtained from Cladosporium cladosporioides LD-8. Their structures were elucidated by comprehensive analysis of NMR and HRESIMS data, as well as ECD calculations. Compounds 1 and 2 possess a novel 6/6/5-fused tricyclic scaffold. Most of the compounds exhibited remarkable antifungal activities against the tested phytopathogenic fungi. Among them, compounds 7, 10, and 16 showed excellent activities with IC50 values ranging from 1.71 to 16.63 μg/mL. Their inhibitory activities against A. brassicicola and A. alternata were higher than that of the commercial fungicide hymexazol. Compound 16 displayed potent in vivo antifungal activity against A. solani at 100 μg/mL with an inhibitory rate of 96.82%. The structure-activity relationship of antifungal australifungin analogues was analyzed for the first time. Therefore, our study provides promising candidates for the development of new fungicides for plant protection.

Novel Essential Oil-Based Thiosemicarbazone Compounds as Potential Fungicides in Controlling Postharvest Diseases of Citrus Fruit

To develop novel fungicides for controlling postharvest fungal diseases in citrus fruits, 12 essential oil (EO)-based thiosemicarbazones compounds, termed hydrazine-carbothioamide, were prepared according to the condensation method. In vitro assays showed that compound 13j exhibited the strongest antifungal activity (minimum inhibitory concentration [MIC] = minimum fungicidal concentration [MFC] = 0.0125 mg/mL) against Penicillium digitatum. An in vivo study revealed that 5 × MFC of compound 13j can effectively mitigate the green mold incidence of citrus fruit inoculated with P. digitatum, as well as fruit rot during natural storage, at a level comparable to that of the chemical fungicide prochloraz. Throughout this process, fruit quality was maintained. The hemolysis assay showed that these thiosemicarbazone compounds have good biocompatibility and that their safety is comparable to that of prochloraz. The antifungal activity of compound 13j was attributed to membrane damage, as confirmed using scanning electron microscopy (SEM), Calcofluor white (CFW) staining, propidium iodide (PI) staining, Fourier transform-infrared (FT-IR) spectroscopy, optical density (OD)260, and relative conductivity assays. Collectively, our results indicate that compound 13j can be used as an antifungal agent to control the postharvest decay of citrus fruits.

Characterization of Lomofungin Gene Cluster Enables the Biosynthesis of Related Phenazine Derivatives

Phenazine-based small molecules are nitrogen-containing heterocyclic compounds with diverse bioactivities and electron transfer properties that exhibit promising applications in pharmaceutical and electrochemical industries. However, the biosynthetic mechanism of highly substituted natural phenazines remains poorly understood. In this study, we report the direct cloning and heterologous expression of the lomofungin biosynthetic gene cluster (BGC) from Streptomyces lomondensis S015. Reconstruction and overexpression of the BGCs in Streptomyces coelicolor M1152 resulted in eight phenazine derivatives including two novel hybrid phenazine metabolites, and the biosynthetic pathway of lomofungin was proposed. Furthermore, gene deletion suggested that NAD(P)H-dependent oxidoreductase gene lomo14 is a nonessential gene in the biosynthesis of lomofungin. Cytotoxicity evaluation of the isolated phenazines and lomofungin was performed. Specifically, lomofungin shows substantial inhibition against two human cancer cells, HCT116 and 5637. These results provide insights into the biosynthetic mechanism of lomofungin, which will be useful for the directed biosynthesis of natural phenazine derivatives.

Cytotoxic glutarimide-containing polyketides isolated from Streptomyces sp. JCM 4793

Glutarimide-containing polyketides usually exhibit anti-fungi activity, which was well exampled by cycloheximide. In our work, three new polyketide structures, 12-amidestreptimidone (1), 12-carboxylstreptimidone (2) and 3-(5S,8R)-(2-amino-2-oxoethyl-2'-methoxy-2'-oxoethyl)-8,10-dimethyl-7-oxododeca-5-hydroxy-9E,11-diolefin (3) were isolated from Streptomyces sp. JCM 4793. 3 without the glutarimide moiety is not active against fungi as expected, while 1 bearing the amide moiety is much more active than its carboxylic form 2. Here we report the isolation, structural elucidation, antifungal activity, and proposed biosynthesis pathway of 1-3.

Synthesis and Antifungal Activities of Novel Griseofulvin Derivatives as Potential Anti-Phytopathogenic Fungi Agents

The extensive and repeated application of chemical fungicides results in the rapid development of fungicide resistance. Novel antifungal pesticides are urgently required. Natural products have been considered precious sources of pesticides. It is necessary to discover antifungal pesticides by using natural products. Herein, 42 various griseofulvin derivatives were synthesized. Their antifungal activities were evaluated in vitro. Most of them showed good antifungal activity, especially 3d exhibited a very broad antifungal spectrum and the most significant activities against 7 phytopathogenic fungi. In vivo activity results suggested that 3d protected apples and tomatoes from serious infection by phytopathogenic fungi. These proved that 3d had the potential to be a natural product-derived antiphytopathogenic fungi agent. Furthermore, docking analysis suggested that tubulin might be one of the action sites of 3d. It is reasonable to believe that griseofulvin derivatives are worth further development for the discovery of new pesticides.

Natural Substances as Valuable Alternative for Improving Conventional Antifungal Chemotherapy: Lights and Shadows

Fungi are eukaryotic organisms with relatively few pathogenic members dangerous for humans, usually acting as opportunistic infections. In the last decades, several life-threatening fungal infections have risen mostly associated with the worldwide extension of chronic diseases and immunosuppression. The available antifungal therapies cannot combat this challenge because the arsenal of compounds is scarce and displays low selective action, significant adverse effects, and increasing resistance. A growing isolation of outbreaks triggered by fungal species formerly considered innocuous is being recorded. From ancient times, natural substances harvested from plants have been applied to folk medicine and some of them recently emerged as promising antifungals. The most used are briefly revised herein. Combinations of chemotherapeutic drugs with natural products to obtain more efficient and gentle treatments are also revised. Nevertheless, considerable research work is still necessary before their clinical use can be generally accepted. Many natural products have a highly complex chemical composition, with the active principles still partially unknown. Here, we survey the field underlying lights and shadows of both groups. More studies involving clinical strains are necessary, but we illustrate this matter by discussing the potential clinical applications of combined carnosic acid plus propolis formulations.

Four unreported aporphine alkaloids with antifungal activities from Artabotrys hexapetalus

In this study, the extract from Artabotrys hexapetalus showed strong antifungal activity against phytopathogenic fungi in vitro. Four unreported aporphine alkaloids, hexapetalusine A-D (1-4), were isolated from stems and roots of Artabotrys hexapetalus (L.f.) Bhandari, along with six known aporphine alkaloids (5-10). Their chemical structures were elucidated by extensive spectroscopic analysis. The absolute configurations of 1-3 were determined using single-crystal X-ray diffractions and ECD calculations. Hexapetalusine A-C (1-3) were special amidic isomers. Additionally, all isolated compounds were evaluated for their antifungal activity against four phytopathogenic fungi in vitro. Hexapetalusine D (4) exhibited weak antifungal activity against Curvularia lunata. Liriodenine (5) displayed significant antifungal activity against Fusarium proliferatum and Fusarium oxysporum f. sp. vasinfectum, which is obviously better than positive control nystatin, suggesting that it had great potential to be developed into an effective and eco-friendly fungicide.

Design, Synthesis, Structure-Activity Relationship, and Three-Dimensional Quantitative Structure-Activity Relationship of Fusarium Acid Derivatives and Analogues as Potential Fungicides

In research related to fungicides, the development of compounds from natural products with high antifungal activity has attracted considerable attention. Fusaric acid (FA), an alkaloid isolated from the metabolites of Fusarium oxysporum, is an important precursor for developing pharmacologically active herbicides. In our previous work, we reported that FA has a wide range of inhibitory activities against 14 plant pathogenic fungi. In particular, it exhibited excellent antifugal effects on Colletotrichum higginsianum (EC50 = 31.7 μg/mL). Herein, to explore the practical application in the agricultural field, the design and synthesis of three series of FA derivatives and their inhibitory activities against plant pathogenic fungi were examined. Results demonstrated that the optimized FA derivatives had excellent inhibitory activities against C. higginsianum, Helminthosporium (Harpophora maydis), and Pyricularia grisea. In particular, the inhibitory activities were considerably improved when the 5-butyl groups of FA were substituted. The EC50 of C. higginsianum and P. grisea was only 1.2 and 12.0 μg/mL when 5-butylalkyl groups were substituted with 5-([1,1'-biphenyl]-4-yl) and 5-phenyl, respectively. Moreover, the safety index of target compounds, which was obtained from the treatment index of medicines, on rice seeds was evaluated. Finally, 16 leading compounds (H4, H22-H24, H27, H29, H30-H34, H37, H45, H50, H52, and H53) were obtained; they had considerable potential for additional modification and optimization as agricultural fungicides. Moreover, three-dimensional quantitative structure-activity relationship models were developed for obtaining a systematic structure-activity relationship profile to explore the possibility of more potent FA derivatives as novel fungicides.

Design, Synthesis, and Antifungal Activities of Novel Carboxamides Derivatives Bearing a Chalcone Scaffold as Potential SDHIs

In search for SDHIs fungicides, twenty-five novel carboxamides containing a chalcone scaffold were designed, synthesized, and evaluated for antifungal activities against five pathogenic fungi. The results showed that compound 5 k exhibited outstanding antifungal activity against R. solani with an EC50 value of 0.20 μg/mL, which was much better than that of commercial SDHIs Boscalid (EC50 =0.74 μg/mL). Moreover, compound 5 k also displayed promising antifungal activities against S. sclerotiorum, B. cinerea, and A. alternate (IC50 =2.53-4.06 μg/mL), indicating that 5 k had broad-spectrum antifungal activity. Additionally, in vivo antifungal activities results showed that 5 k could significantly inhibit the growth of R. solani in rice leaves with good protective efficacy (57.78 %) and curative efficacy (58.45 %) at 100 μg/mL, both of which were much better than those of Boscalid, indicating a promising application prospect. Moreover, SEM analysis showed that compound 5 k could remarkably disrupt the typical structure and morphology of R. solani hyphae. Further SDH enzyme inhibition assay and molecular docking study revealed that lead compound 5 k had a similar mechanism of action as commercial SDHI Boscalid. These results indicated that compound 5 k showed potential as a SDHIs fungicide and deserved further investigation.