Design, Synthesis and Antifungal Activity of Coumarin Ring-Opening Derivatives

3D-QSAR-Directed Synthesis of Halogenated Coumarin-3-Hydrazide Derivatives: Unveiling Their Potential as SDHI Antifungal Agents

The pursuit of new succinate dehydrogenase (SDH) inhibitors is a leading edge in fungicide research and development. The use of 3D quantitative structure-activity relationship (3D-QSAR) models significantly enhances the development of compounds with potent antifungal properties. In this study, we leveraged the natural product coumarin as a molecular scaffold to synthesize 74 novel 3-coumarin hydrazide derivatives. Notably, compounds 4ap (0.28 μg/mL), 6ae (0.32 μg/mL), and 6ah (0.48 μg/mL) exhibited exceptional in vitro effectiveness against Rhizoctonia solani, outperforming the commonly used fungicide boscalid (0.52 μg/mL). Furthermore, compounds 4ak (0.88 μg/mL), 6ae (0.61 μg/mL), 6ah (0.65 μg/mL), and 6ak (1.11 μg/mL) showed significant activity against Colletotrichum orbiculare, surpassing both the SDHI fungicide boscalid (43.45 μg/mL) and the broad-spectrum fungicide carbendazim (2.15 μg/mL). Molecular docking studies and SDH enzyme assays indicate that compound 4ah may serve as a promising SDHI fungicide. Our ongoing research aims to refine this 3D-QSAR model further, enhance molecular design, and conduct additional bioactivity assays.

Design, Synthesis, Antifungal Activity, and 3D-QASR of Novel Oxime Ether-Containing Coumarin Derivatives as Potential Fungicides

Structural modification of natural products is an effective approach for improving antifungal activity and has, therefore, been used extensively in the development of new agrochemical products. In this work, a series of novel coumarin derivatives containing oxime ether structures were designed, synthesized, and evaluated for antifungal activity. Some of the designed compounds exhibited promising antifungal activities against tested fungi, and compounds 4a, 4c, 5a, and 6b had EC50 values equivalent to those of commercial fungicides. Compound 6b was the most promising candidate fungicide against Rhizoctonia solani (EC50 = 0.46 μg/mL). In vivo antifungal bioassays suggested that compounds 5a and 6b could serve as novel agricultural antifungals. Furthermore, microscopy demonstrated that compound 6b induced the sprawling growth of hyphae, distorted the outline of cell walls, and reduced mitochondrial numbers. Additionally, the effects of the substituent steric, electrostatic, hydrophobic, and hydrogen-bond fields were elucidated using an accurate and reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) model. The results presented here will guide the discovery of potential novel fungicides for plant disease control in agriculture.

Polyphenolic glycosides with unusual four-membered ring possessing anti-Parkinson's disease potential from black wolfberry

This work reports the isolation of seven undescribed polyphenolic glycosides (1-7) together with fourteen known compounds (8-21) from the fruit of Lycium ruthenicum Murray. The structures of the undescribed compounds were identified based on comprehensive spectroscopic methods including IR, HRESIMS, NMR and ECD, and chemical hydrolysis. Compounds 1-3 possess an unusual four-membered ring, while 11-15 were firstly isolated from this fruit. Interestingly, compounds 1-3 inhibited monoamine oxidase B with IC₅₀ of 25.36 ± 0.44, 35.36 ± 0.54, and 25.12 ± 1.59 μM, respectively, and showed significant neuroprotective effect on PC12 cells injured by 6-OHDA. Moreover, compound 1 improved the lifespan, dopamine level, climbing behaviour, and olfactory ability of the PINK1^B9 flies, a Drosophila model of Parkinson's disease. This work presents the first in vivo neuroprotective evidence of the small molecular compounds in L. ruthenicum Murray fruit, indicating its good potential as neuroprotectant.

The mechanism of coumarin inhibits germination of ryegrass (Lolium perenne) and its application as coumarin-carbon dots nanocomposites

BACKGROUND

As an important plant allelochemical, coumarin can effectively inhibit the germination of various seeds. However, little is known about the inhibition mechanism of coumarin on weed seed germination. Moreover, the herbicidal activity of coumarin is needed to be improved as a natural pesticide.

RESULTS

Coumarin had the highest inhibition effect on the ryegrass (Lolium perenne) seed, where coumarin disturbed the hormone pathway by decreasing the content of gibberellic acid 3, resulting in the reduction of amylase activity and consumption of starch during the germination process of ryegrass seed. Moreover, coumarin induced decreased activity of catalase and subsequently led to the accumulation of hydrogen peroxide and malondialdehyde, causing oxidative stress during the germination process of ryegrass seed. Furthermore, to enhance the herbicidal activity of coumarin, carbon dots (CDs) modified with polyetherimide were prepared, characterized, and then combined with coumarin to form coumarin-carbon dots (Cm-CDs) nanocomposites. Compared with coumarin, Cm-CDs nanocomposites significantly increased the herbicidal activity of coumarin on ryegrass, which implies that Cm-CDs nanocomposites could be used as a potential formulation to improve the herbicidal activity of coumarin.

CONCLUSION

This study not only reveals the mechanism of coumarin on ryegrass germination, but also develop Cm-CDs nanocomposites to enhance the herbicidal activity of coumarin. Our findings will stimulate the application of Cm-CDs nanomaterials as an effective and environmentally friendly formulation in agriculture. © 2023 Society of Chemical Industry.

Selectfluor-Enabled C(sp3)-H Alkoxylation of 3-Methylfuranocoumarins

A facile and metal-free method for the direct C(sp³)-H bond alkoxylation of 3-methylfuranocoumarins with alcohols has been disclosed. Selectfluor enabled the (hetero)benzylic C-H etherification by tuning the reaction temperature and solvent. Various alcohols were compatible in this transformation with suitable yields. The mechanistic studies revealed that the reaction might undergo the double addition process of alcohols, as well as the departure of a fluoride anion and the formation of an oxonium ion.

Novel Fluorinated 7-Hydroxycoumarin Derivatives Containing an Oxime Ether Moiety: Design, Synthesis, Crystal Structure and Biological Evaluation

A series of fluorinated 7-hydroxycoumarin derivatives containing an oxime ether moiety have been designed, synthesized and evaluated for their antifungal activity. All the target compounds were determined by ¹H-NMR, ¹³C-NMR, FTIR and HR-MS spectra. The single-crystal structures of compounds 4e, 4h, 5h and 6c were further confirmed using X-ray diffraction. The antifungal activities against Botrytis cinerea (B. cinerea), Alternariasolani (A. solani), Gibberella zeae (G. zeae), Rhizoctorzia solani (R. solani), Colletotrichum orbiculare (C. orbiculare) and Alternaria alternata (A. alternata) were evaluated in vitro. The preliminary bioassays showed that some of the designed compounds displayed the promising antifungal activities against the above tested fungi. Strikingly, the target compounds 5f and 6h exhibited outstanding antifungal activity against B. cinerea at 100 μg/mL, with the corresponding inhibition rates reached 90.1 and 85.0%, which were better than the positive control Osthole (83.6%) and Azoxystrobin (46.5%). The compound 5f was identified as the promising fungicide candidate against B. cinerea with the EC₅₀ values of 5.75 μg/mL, which was obviously better than Osthole (33.20 μg/mL) and Azoxystrobin (64.95 μg/mL). Meanwhile, the compound 5f showed remarkable antifungal activities against R. solani with the EC₅₀ values of 28.96 μg/mL, which was better than Osthole (67.18 μg/mL) and equivalent to Azoxystrobin (21.34 μg/mL). The results provide a significant foundation for the search of novel fluorinated 7-hydroxycoumarin derivatives with good antifungal activity.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.

Promising antifungal agents: A minireview

In the recent past, prevalence of life threatening fungal diseases have increased rapidly in immune-compromised cases such as acquired immunodeficiency syndrome (AIDS), cancer, organ transplant etc. Side by side, the appearance of drug resistance to the presently available antifungal therapeutics is on a rapid rise. It has become a top priority for the academia and pharmaceutical industries to develop new antifungal agents able to combat this resistance, and at the same time, possess potential broad spectrum of activity and minimum toxicity. An understanding of the pharmacological interactions between antifungal agents and their targets offers opportunities for design of new therapeutics. This review discusses the various methodology of drug design, structure activity relationships (SARs), and mode of action of variety of new antifungal agents.

Organophotoredox Catalysis: Visible-light-induced Multicomponent Synthesis of Chromeno[4, 3-b]chromene and Hexahydro-1H-xanthene Derivatives

Background:

In recent years, photoredox catalysis using eosin Y has gained considerable significance in organic chemistry. It is evolving as a powerful approach in modern organic synthesis for the activation of small molecules.

Objective:

The use of organic dyes to convert visible light into chemical energy by involving a single-electron transfer with organic substrates has innumerable applications.

Method and Results:

The present strategy is the first example of visible light promoted, aerobic, oxidative cyclization of chromeno[4,3-b]chromenes and hexahydro-1H-xanthenes via the formation of C–O and C–C bonds to afford excellent yield of the products in a simple one-pot operation under mild reaction conditions.

Conclusion:

The major advantages of the present methodology include short reaction time, cost effectiveness, easy work-up, broad substrate scope and high atom economy.

Design, synthesis and antifungal activities of novel pyrrole- and pyrazole-substituted coumarin derivatives

We synthesized a series of novel pyrrole- and pyrazole-substituted coumarin derivatives and evaluated their antifungal activity against six phytopathogenic fungi in vitro. The primary assay results demonstrated that some designed compounds displayed potent activities. Among them, compounds 5g, 6a, 6b, 6c, 6d and 6h exhibited more effective control than Osthole against Cucumber anthrax and Alternaria leaf spot. Furthermore, compound 5g displayed stronger antifungal activity against Rhizoctorzia solani (EC₅₀ = 15.4 µg/mL) than positive control Osthole (EC₅₀ = 67.2 µg/mL).

Design, synthesis and antifungal activity evaluation of coumarin-3-carboxamide derivatives

A series of coumarin-3-carboxamides/hydrazides have been designed and synthesized, all the target compounds were evaluated in vitro for their antifungal activity against Botrytis cinerea, Alternaria solani, Gibberella zeae, Rhizoctorzia solani, Cucumber anthrax and Alternaria leaf spot, some of the designed compounds 4a-4g exhibited potential activity in the primary assays, this highlighted by the compounds 4a, 4d, 4e and 4f, EC₅₀ values of which against Rhizoctorzia solani were as low as 1.80 μg/mL, 2.50 μg/mL, 2.25 μg/mL and 2.10 μg/mL, respectively, exhibiting more effective control with that of the positive control than Boscalid. Furthermore, compounds 4a and 4e represented equivalent antifungal activity with Boscalid against Botrytis cinerea.

Activity of the pterophyllins 2 and 4 against postharvest fruit pathogenic fungi. Comparison with a synthetic analog and related intermediates

The antifungal activity of pterophyllin 2, pterophyllin 4, a 5-desmethyl analog of the latter and some of their synthetic intermediates, against three postharvest phytopathogenic fungi, was evaluated. The target fungi were Rhizopus stolonifer, Botrytis cinerea and Monilinia fructicola, which affect fruits worldwide, causing important economic losses. The tests were carried out with imazalil and carbendazim as positive controls. Minimum inhibitory concentrations and minimum fungicidal concentrations were determined, and the morphology of the colonies was examined microscopically. In liquid medium, it was found that pterophyllin 4 exhibited selective fungicidal activity toward M. fructicola, whereas its congener pterophyllin 2 proved to be less potent and not selective and the 5-desmethyl analog of pterophyllin 4 displayed a different activity profile. Morphological changes were observed in the colonies exposed to pterophyllin 4. The results highlighted the importance of small structural features for the antifungal behavior and also suggested that, in Nature, the pterophyllins may act as plant defenses against pathogens.

Design, Synthesis and Antifungal Activity of Psoralen Derivatives

A series of linear furanocoumarins with different substituents have been designed and synthesized. Their structures were confirmed by ¹H-NMR spectroscopy, high resolution mass spectra (EI-MS), IR, and X-ray single-crystal diffraction. All of the target compounds were evaluated in vitro for their antifungal activity against Rhizoctorzia solani, Botrytis cinerea, Alternaria solani, Gibberella zeae, Cucumber anthrax, and Alternaria leaf spot at 100 μg/mL, and some of the designed compounds exhibited potential antifungal activities. Compound 3a (67.9%) exhibited higher activity than the control Osthole (66.1%) against Botrytis cinerea. Furthermore, compound 4b (62.4%) represented equivalent antifungal activity as Osthole (69.5%) against Rhizoctonia solani. The structure-activity relationship (SAR) study demonstrates that linear furanocoumarin moiety has an important effect on the antifungal activity, promoting the idea of the coumarin ring as a framework that might be exploited in the future.