Synthesis of sulfonate derivatives of maltol and their biological activity against Phytophthora capsici and Bursaphelenchus xylophilus in vitro

Design, synthesis, and anti-oomycete activity of 3-acyloxymaltol/ethyl maltol derivatives

Twenty 3-acyloxymaltol/ethyl maltol derivatives (7a-j and 8a-j) were synthesized and evaluated in vitro for their anti-oomycete activity against Phytophthora capsici, respectively. Among all of twenty derivatives, more than half of the compounds 7f, 7h, 8a-h and 8j had anti-oomycete activity higher than the positive control zoxamide (EC50 = 22.23 mg/L), and the EC50 values of 18.66, 20.32, 12.80, 16.18, 10.59, 14.98, 16.80, 10.36, 15.32, 12.64, and 13.59 mg/L, respectively. Especially, compounds 8c and 8f exhibited the best anti-oomycete activity against P. capsici with EC50 values of 10.59 and 10.36 mg/L, respectively. Overall, hydroxyl group of maltol/ethyl maltol is important active modification site.

Current Status and Prospects of Pine Wilt Disease Management with Phytochemicals-A Review

PWD (pine wilt disease) is a devastating forest disease caused by the Bursaphelenchus xylophilus, which is the major invasive species in Asian and European countries. To control this disease, fumigation, pesticide injection, and clear cutting of epidemic trees have been widely used. But these management strategies have many limitations in terms of the effectiveness and environmental impacts, especially for the overuse of chemical pesticides. Thus, PCs (phytochemicals), the various compounds extracted from plants, have drawn extensive attention owing to their special characteristics, including abundant sources, low toxicity, high efficacy, and easy degradation. This review provides an overview of the current status of using PCs as alternative approaches to manage PWD. It discusses the efficacy of various PCs, the factors influencing their nematicidal activity, and their mechanism of action against B. xylophilus. These results will reveal the application of PCs in combating these devastating diseases and the necessity for further research.

Design, synthesis and anti-oomycete activity of 2-acyloxyhinokitiol derivatives

In order to explore novel natural product-based anti-oomycete agent, ten 2-acyloxyhinokitiol derivatives (5a-j) were designed and synthesised, and structurally confirmed by 1H NMR,13C NMR, HRMS, and melting point. The stereochemical configuration of compound 5f was unambiguously confirmed by single-crystal X-ray diffraction. Furthermore, we evaluated the target compounds 5a-j as anti-oomycete activity against a serious agricultural disease of Phytophthora capsici. Among the ten hinokitiol ester derivatives tested, four compounds 5d, 5g, 5h and 5j had anti-oomycete activity higher than the positive control zoxamide (EC50 = 23.59 mg/L), and the EC50 values of 18.90, 20.62, 13.61 and 21.29 mg/L, respectively. Especially compound 5h exhibited the best anti-oomycete activity against P. capsici with EC50 value of 13.61 mg/L. Overall, the anti-oomycete activities of 2-acyloxyhinokitiol derivatives is higher than that of 2-sulfonyloxyhinokitiol derivatives. The results laid a good foundation for the subsequent synthesis of hinokitiol ester derivatives with significant anti-oomycete activity.

Semisynthesis, anti-oomycete and anti-fungal activities of ursolic acid ester derivatives

Using ursolic acid (UA) as the lead compound, thirteen UA ester derivatives (3 and 7a-l) were synthesized by modifying their C-3 and C-28 positions, respectively, and their structures were well characterized by 1H NMR, 13C NMR, HRMS and melting points. Furthermore, we evaluated the anti-oomycete and anti-fungal activities of these compounds against Phytophthora capsici and Fusarium graminearum in vitro. The results showed that compound 7h exhibited prominent anti-oomycete and anti-fungal activities, and the median effective concentration (EC50) values of 7h against P. capsici and F. graminearum were 70.49 and 113.21 mg/L, respectively. This study suggested that the anti-oomycete and anti-fungal activities of esters synthesized by introducing acyloxy group at C-3 position of UA was more conspicuous than that of esters synthesized by introducing benzyloxy group at C-28 position. This result will pave the way for further modification of UA to develop potential new fungicides.

Sulfonate Derivatives Containing a Kakuol Moiety as Potential Fungicidal Candidates: Design, Synthesis and Antifungal Activity Evaluation

As a part of our continuing exploration to discover new potential promising fungicide candidates, eighteen sulfonate derivatives (3a-3r) containing a kakuol moiety were designed and synthesized. Synthetic sulfonate derivatives were tested comprehensively for antifungal activities against four plant pathogenic fungi (Botrytis (B.) cinerea, Valsa (V.) mali, Fusarium (F.) graminearum, Sclerotinia (S.) sclerotiorum), and their structure activity relationships were summarized. Especially, derivatives 3i and 3j exhibited remarkable activity against V. mali, with the inhibition rates of 99.8 and 100%, which were slightly superior to that of carbendazim (98.9%), a reference fungicide. Moreover, derivatives 3a, 3k and 3q possess the broader antifungal spectrum against three tested plant pathogenic fungi with inhibition rates over 60%. Structure-activity relationship (SAR) analysis indicated that the introduction of 2-F or 3-F into the benzene ring would give rise to a remarkable increase of the antifungal activity against V. mali.

Synthesis of novel 18β-glycyrrhetinic acid sulfonate derivatives displaying significant anti-oomycete activity against Phytophthora capsici

Using 18β-glycyrrhetinic acid (GA) as the lead compound, fourteen GA sulphonate derivatives (3a-n) were prepared by modifying its C-3 OH group, and their structures were well confirmed by 1H NMR, 13C NMR, HRMS and melting points. Moreover, we screened the anti-oomycete activity of these compounds against Phytophthora capsici by using the mycelial growth rate method. Among the fourteen GA sulphonate derivatives evaluated, four compounds 3f, 3j, 3k and 3l exhibited more potent anti-oomycete activity than that of the positive control zoxamide (EC50 = 25.17 mg/L), and had the median effective concentration (EC50) values of 23.04, 16.16, 22.55, and 13.93 mg/L, respectively. Especially compound 3l showed the best anti-oomycete activity against P. capsici with EC50 value of 13.93 mg/L. Overall, the introduction of sulfonyloxy groups at the C-3 position of GA has a significant impact on its anti-oomycete activity, and the corresponding derivative activity varies significantly with different substituents R.

Synthesis, Anti-Oomycete and Anti-fungal Activities of Novel Cinchona Alkaloid Derivatives Containing Sulfonate Moiety

Using cinchona alkaloid as the lead compound, twenty-four cinchona alkaloid sulfonate derivatives (1 a-l, 2 a-c, 3 a-c, 4 a-c, and 5 a-c) were designed and prepared by modifying their C9 position, and structurally confirmed by 1 H-NMR, 13 C-NMR, HR-MS and melting points. Moreover, the stereochemical configurations of compounds 1 f and 1 l were unambiguously confirmed by single-crystal X-ray diffraction. Furthermore, we determined the anti-oomycete and anti-fungal activities of these target compounds against Phytophthora capsici and Fusarium graminearum in vitro. The results showed that two compounds 4 b and 4 c exhibited prominent anti-oomycete activity, and the median effective concentration (EC50 ) values of 4 b and 4 c against P. capsici were 22.55 and 16.32 mg/L, respectively. This study suggested that when the C9 position of cinchona alkaloid sulfonate derivatives is in the S configuration and the 6'-position methoxy group is not present, the anti-oomycete activity is superior. In addition, five compounds 1 e, 1 f, 1 k, 3 c and 4 c displayed significant anti-fungal activity, with EC50 values of 43.64, 45.07, 80.18, 48.58 and 41.88 mg/L against F. graminearum, respectively. This result indicates that only when a specific substituent is introduced into the structural framework of the target compound, the corresponding compound exhibits significant inhibitory activity against fungi.

Synthesis of hinokitiol sulfonate derivatives and their anti-oomycete and nematicidal activities

In order to explore novel natural product-based anti-oomycete and nematicidal agents, sixteen unreported 2-sulfonyloxyhinokitiol derivatives were prepared using the principle of active splicing, and structurally confirmed by proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance (13C NMR), high-resolution mass spectrometry (HRMS), and melting point. Moreover, we evaluated the title compounds as anti-oomycete and nematicidal agents against two serious agricultural pests of Phytophthora capsici and Meloidogyne incongnita. Among the sixteen hinokitiol esters tested: (1) Compounds 3a and 3m exhibited the most potent anti-oomycete activity compared to zoxamide against P. capsici, and the median effective concentration (EC50) values of 3a, 3m, and zoxamide were 18.64, 21.11, and 23.15 mg/L, respectively; Further studies showed that the existence of seven membered ring and carbonyl group was the necessary condition for the high anti-oomycete activity of hinokitiol. (2) Compounds 3n and 3p exhibited more promising nematicidal activity than hinokitiol, and the median lethal concentration (LC50) values of 3n, 3p and 1 against M. incongnita were 0.2111, 0.2079, and 0.3933 mg/L, respectively. This result will pave the way for further modification of hinokitiol to develop potential new fungicides and nematicides.

Synthesis and Anti-Oomycete Preliminary Mechanism of Sulfonate Derivatives of Ethyl Maltol

To discover novel molecules with unique mechanism against plant pathogenic oomycetes, sixteen new sulfonate derivatives of ethyl maltol (3a-p) were synthesized by structural modification of 2-ethyl-3-hydroxy-4H-pyran-4-one, and their anti-oomycete activity against a serious agricultural disease, Phytophthora capsici Leonian was determined in this study. Among all tested compounds, derivatives 3e, 3m and 3p exhibited the most potent anti-oomycete activity against P. capsici with EC₅₀ values of 19.40, 21.04 and 31.10 mg/L, respectively; especially 3e and 3m showed the best promising and pronounced anti-oomycete activity than zoxamide (EC₅₀ =26.87 mg/L). The results further proved that 4-tert-butylphenylsulfonyl group, 3-nitro-4-chlorophenylsulfonyl group and 8-quinolinesulfonyl group introduced at the hydroxy position of ethyl maltol or maltol were necessary for obtaining the most potent compounds. Further mechanism studies of P. capsici treated with 3e demonstrated that this compound can affect the growth of mycelia by disrupting the integrity of the membrane, and the higher the concentration of the compound is, the greater the degree of membrane integrity damage. These important results will pave the way for further modification of ethyl maltol to develop potential new fungicides.

Synthesis and Anti-Oomycete Activity of Sulfonate Derivatives of Fenjuntong

In order to discover highly active fungicides, sixteen novel sulfonate derivatives of Fenjuntong were synthesized by structural modification of 2'-hydroxybutyrophenone, and their anti-oomycete activity against Phytophthora capsici Leonian was determined in this study. Among all tested compounds, compound 3b displayed more significant anti-oomycete activity than the precursor Fenjuntong against P. capsici, and the EC₅₀ values of 3b and Fenjuntong were 84.50 and 517.25 mg/L, respectively. By comparing the anti-oomycete activity of compounds 3a-p, I-a-p, and II-a-p, the following conclusions were drawn: (1) Hydroxy group is well tolerated, and sulfonylation of hydroxy group enhances its anti-oomycete activity. (2) The proper length of the ketone carbonyl chain is very important for their anti-oomycete activity. (3) The presence of a site methoxy group in the structural skeleton is closely related to the anti-oomycete activity. These important results will pave the way for further modification of Fenjuntong to develop potential new fungicides.

Synthesis of novel 3/5(3,5)-(di)nitropaeonol hydrazone derivatives as nematicidal agents

Eighteen novel 3/5(3,5)-(di)nitropaeonol hydrazone derivatives were prepared, and their structures well characterized by ¹H NMR, HRMS, and mp. Due to the steric hindrance, the substituents on the C = N double bond of all hydrazine compounds (except E/Z = 4/1 for IV-1g, IV-1l, IV-2b, and E/Z = 3/2 for IV-1n, IV-3a) adopted E configuration. Among all compounds, four compounds 2, 4, IV-1j, and IV-1n exhibited potent nematicidal activity than their precursor paeonol, especially 5-nitropaeonol (2) and 3,5-dinitropaeonol (4) displayed the most potent nematicidal activity Heterodera glycines in vivo with LC₅₀ values of 32.3307 and 36.7074 mg/L, respectively.

Combinatorial Synthesis of Novel 1-Sulfonyloxy/acyloxyeugenol Derivatives as Fungicidal Agents

BACKGROUND

Developing the high-efficiency and low-risk small-molecule green-fungicide is the key to effective control of the plant pathogenic oomycetes. Essential oils play a very important role in novel fungicide discovery for their unique sources and potential target sites. Eugenol, a kind of plant essential oil, was mainly isolated from the unopened and dried flower buds of Syzygium aromaticum of the Myrtaceae family. Due to its unique structural skeleton, eugenol and its derivatives have exhibited a wide range of biological activities. However, study on the synthesis of novel 1-sulfonyloxy/acyloxyeugenol derivatives as fungicidal agents against Phytophthora capsici has not yet been reported.

METHODS

Twenty-six novel 1-sulfonyloxy/acyloxyeugenol derivatives (3a-p and 5a-j) were prepared and their structures were well characterized by 1H NMR, HRMS, and m.p.. Their fungicidal activity was evaluated against P. capsici by using the mycelial growth rate method.

RESULTS

To find novel natural-product-based fungicidal agents to control the plant pathogenic oomycetes, we herein designed and synthesized two series of novel 1-sulfonyloxy/acyloxyeugenol derivatives (3a-p and 5a-j) as fungicidal agents against P. capsici Leonian, in vitro. Results of fungicidal activity revealed that, among all compounds, especially compounds 3a, 3f, and 3n displayed the most potent anti-oomycete activity against P. capsici with EC50 values of 79.05, 75.05, and 70.80, respectively.

CONCLUSION

The results revealed that the anti-oomycete activity of eugenol with the sulfonyloxy group was higher than that with the acyloxy group. It is suggested that the fungicidal activity of eugenol can be improved by introducing the sulfonyloxy group. This will pave the way for further design, structural modification, and to develop eugenol derivatives as fungicidal agents.

Synthesis and Anti-Oomycete Activity of 1-Sulfonyloxy/Acyloxydihydroeugenol Derivatives

Endeavor to discover biorational natural products-based fungicides, two series (26) of novel 1-sulfonyloxy/acyloxydihydroeugenol derivatives (3a-p and 5a-j) were prepared and assessed for their fungicidal activity against P. capsici Leonian, in vitro. Results of fungicidal activity revealed that, among all compounds, especially compounds 3a, 5c, and 5e displayed the most potent anti-oomycete activity against P. capsici with EC₅₀ values of 69.33, 68.81, and 67.77 mg/L, respectively. Overall, the anti-oomycete activities of 1-acyloxydihydroeugenol derivatives (5a-j) were higher than that of 1-sulfonyloxydihydroeugenol derivatives (3a-p). It is proved that the introduction of the acyl group at hydroxy position of dihydroeugenol is more beneficial to improve its anti-oomycete activity than that of the sulfonyl group. These preliminary results will pave the way for further modification of dihydroeugenol in the development of potential new fungicides.

Design and synthesis of novel n-butyphthalide derivatives as promising botanical fungicides

In order to obtain novel botanical fungicides, three series of novel 6-substituted n-butyphthalide derivatives have been designed and synthesized via nucleophilic addition, reduction, nitrification, amination, sulfonation, Sandmeyer and Suzuki reaction. The mycelium growth rate method was used to evaluate the inhibition activity against eight phytopathogenic fungi in vitro. Preliminary bioassay tests showed that compounds 6f, 6n, 6p, 6r and 7a exhibited better activity for some fungi at 50 μg/mL than the positive drug hymexazol and lead compound n-butyphthalide (NBP). The preliminary structure-activity relationships indicated that the antifungal activity is significantly affected by the substituents on the benzene ring.

Combinatorial Synthesis of A Series of Paeonol-based Phenylsulfonyl hydrazone Derivatives as Insecticidal Agents

Background:

Plant secondary metabolites play an essential role in the discovery of novel insecticide due to their unique sources and potential target sites. Paeonol, the main phenolic components in Moutan Cortex, is recognized as a safe and potent botanical insecticide to many insects. The structural modification of paeonol in this study into phenylsulfonylhydrazone derivatives is proved an effective approach for the development of novel insecticides, those derivatives being more toxic than paeonol. However, there have been no reports on the insecticidal activity of paeonol-based phenylsulfonylhydrazone derivatives in controlling Mythimna separata.

Methods:

We have been working to discover biorational natural products-based insecticides. Twelve novel paeonol-based phenylsulfonylhydrazone derivatives have been successfully prepared by structural modification of paeonol, and the insecticidal activity against M. separata by the leafdipping method at the concentration of 1 mg/mL has been evaluated.

Results:

Insecticidal activity revealed that out of 12 title compounds, derivatives 5c and 5f displayed the best against M. separate with the FMR both of 53.6% than toosendanin (FMR = 50.0%).

Conclusion:

The results suggested that for the paeonol-based phenylsulfonylhydrazone series derivatives, the proper substituent of arylsulfonyl R at the hydroxyl position of paeonol was very important for their insecticidal activity. These preliminary results will pave the way for further modification of paeonol in the development of potential new insecticides.