Efficient synthesis of fused bicyclic ethers and their application in herbicide chemistry

4-Hydroxyphenylpyruvate Dioxygenase Inhibitors: From Molecular Design to Synthesis

Weed resistance is a critical issue in crop production. Among the known herbicides, 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are crucial for addressing weed resistance. HPPD inhibitors constitute a pivotal aspect of contemporary crop protection strategies. The advantages of these herbicides are their broad weed spectrum, flexible application, and excellent compatibility with other herbicides. They also exhibit satisfactory crop selectivity and low toxicity and are environmentally friendly. An increasing number of new HPPD inhibitors have been designed by combining computer-aided drug design with conventional design approaches. Herein, the molecular design and structural features of innovative HPPD inhibitors are reviewed to guide the development of new HPPD inhibitors possessing an enhanced biological efficacy.

Design, synthesis and biological activity of novel triketone-containing quinoxaline as HPPD inhibitor

BACKGROUND

4-Hydroxyphenyl pyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the important target enzymes used to address the issue of weed control. HPPD-inhibiting herbicides can reduce the carotenoid content in plants and hinder photosynthesis, eventually causing albinism and death. Exploring novel HPPD-inhibiting herbicides is a significant direction in pesticide research. In the process of exploring new high-efficiency HPPD inhibitors, a series of novel quinoxaline derivatives were designed and synthesized using an active fragment splicing strategy.

RESULTS

The title compounds were unambiguously characterized by infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectroscopy. The results of the in vitro tests indicated that the majority of the title compounds showed potent inhibition of Arabidopsis thaliana HPPD (AtHPPD). Preliminary bioevaluation results revealed that a number of novel compounds displayed better or excellent herbicidal activity against broadleaf and monocotyledonous weeds. Compound III-5 showed herbicidal effects comparable to those of mesotrione at a rate of 150 g of active ingredient (ai)/ha for post-emergence application. The results of molecular dynamics verified that compound III-5 had a more stable protein-binding ability. Molecular docking results showed that compound III-5 and mesotrione shared homologous interplay with the surrounding residues. In addition, the enlarged aromatic ring system adds more force, and the hydrogen bond formed can enhance the synergy with π-π stacking.

CONCLUSIONS

The present work indicates that compound III-5 may be a potential lead structure for the development of new HPPD inhibitors.

Discovery of novel benzofuran scaffold as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. This study sheds new light on the differences in molecular scaffold from commercialized HPPD inhibitors.

RESULTS

The compounds A1-A18 and B1-B27 were synthesized for in vitro and greenhouse experiments. The greenhouse experiment data indicated that compounds B14 and B18 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. In vitro testing indicated that the compounds were HPPD inhibitors. Moreover, molecular simulation results show that the compounds B14, B18, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on crop selectivity results, compounds B14 and B18 were selected for maize studies (injury≤10%), indicating its potential for weed control in maize fields.

CONCLUSION

These results showed that the pyrazole-benzofuran structure could be used as possible lead compounds for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Discovery of novel arylthioacetic acid derivatives as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. In a continuing effort to discover novel HPPD inhibitors, we adopted a bioisosterism strategy to design a series of novel arylthioacetic acid scaffold based on the previously discovered aryloxyacetic acid scaffold. This study sheds new light on the discovery of novel HPPD inhibitors.

RESULTS

The compounds A1-A30 and B1-B39 were prepared through an efficient synthetic route for in vitro and glasshouse experiments (herbicidal activities, herbicidal activity spectrum, and crop selectivity). Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD inhibitors, compounds A11 (K_i = 0.021 μmol L^-1 ) and B20 (K_i = 0.022 μmol L^-1 ), which exhibit similar activities to that of mesotrione (K_i = 0.020 μmol L^-1 ). The glasshouse experiments data indicated that compounds B34 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. Moreover, molecular simulation results show that the compounds B20, B34, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on herbicidal results, compound B34 was selected for crop selectivity studies (corn injury ≤ 10%), indicating its potential for weed control in corn fields.

CONCLUSION

These bioassay results showed that the compound B34 could be used as a possible lead compound for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Synthesis and herbicidal activity of novel pyrazole aromatic ketone analogs as HPPD inhibitor

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been a good target for herbicide discovery. In order to discover novel HPPD herbicides, a series of pyrazole aromatic ketone analogs were designed and synthesized.

RESULTS

The 25 pyrazole aromatic ketone analogs synthesized were tested for herbicidal activity and compounds A1, A3, A4, A17, A20 and A25 displayed excellent herbicidal activity against Chenopodium serotinum, Stellaria media and Brassica juncea at 37.5 g ha^-1 . In addition, compounds A1, A5, A9, A10, A16, A17, A20 and A25 exhibited good crop selectivity for wheat, maize and rice at 150 g ha^-1 . Inhibition activities against AtHPPD proved the compounds were HPPD inhibitors. The structure-activity relationship of these pyrazole aromatic ketone analogs was studied using molecular docking.

CONCLUSION

These pyrazole aromatic ketone derivatives could be used as lead structures for development of HPPD herbicides against dicotyledonous weeds with further structure modification. © 2019 Society of Chemical Industry.

Synthesis and herbicidal activities of aryloxyacetic acid derivatives as HPPD inhibitors

A series of aryloxyacetic acid derivatives were designed and synthesized as 4-hydoxyphenylpyruvate dioxygenase (HPPD) inhibitors. Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD (AtHPPD) inhibitors, in particular compounds I12 (K_i = 0.011 µM) and I23 (K_i = 0.012 µM), which exhibit similar activities to that of mesotrione, a commercial HPPD herbicide (K_i = 0.013 µM). Furthermore, the newly synthesized compounds show significant greenhouse herbicidal activities against tested weeds at dosages of 150 g ai/ha. In particular, II4 exhibited high herbicidal activity for pre-emergence treatment that was slightly better than that of mesotrione. In addition, compound II4 was safe for weed control in maize fields at a rate of 150 g ai/ha, and was identified as the most potent candidate for a novel HPPD inhibitor herbicide. The compounds described herein may provide useful guidance for the design of new HPPD inhibiting herbicides and their modification.

Discovery of N-Aroyl Diketone/Triketone Derivatives as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibiting-Based Herbicides

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is an important target site for discovering new bleaching herbicides. To explore novel HPPD inhibitors with excellent herbicidal activity, a series of novel N-aroyl diketone/triketone derivatives were rationally designed by splicing active groups and bioisosterism. Bioassays revealed that most of these derivatives displayed preferable herbicidal activity against Echinochloa crus-galli (EC) at 0.045 mmol/m² and Abutilon juncea (AJ) at 0.090 mmol/m². In particular, compound I-f was more potent compared to the commercialized compound mesotrione. Molecular docking indicated that the corresponding active molecules of target compounds and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD.

Ammonium NHC-tagged olefin metathesis catalysts – influence of counter-ions on catalytic activity

Ruthenium-based catalysts bearing quaternary ammonium groups in their N-heterocyclic carbene (NHC) fragments and different counter-ions were synthesised and tested in various olefin metathesis transformations.

An Efficient One-Pot Synthesis of 2-(Aryloxyacetyl)cyclohexane-1,3-diones as Herbicidal 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is an important target for new bleaching herbicides discovery. As a continuous work to discover novel crop selective HPPD inhibitor, a series of 2-(aryloxyacetyl)cyclohexane-1,3-diones were rationally designed and synthesized by an efficient one-pot procedure using N,N'-carbonyldiimidazole (CDI), triethylamine, and acetone cyanohydrin in CH₂Cl₂. A total of 58 triketone compounds were synthesized in good to excellent yields. Some of the triketones displayed potent in vitro Arabidopsis thaliana HPPD (AtHPPD) inhibitory activity. 2-(2-((1-Bromonaphthalen-2-yl)oxy)acetyl)-3-hydroxycyclohex-2-en-1-one, II-13, displayed high, broad-spectrum, and postemergent herbicidal activity at the dosage of 37.5-150 g ai/ha, nearly as potent as mesotrione against some weeds. Furthermore, II-13 showed good crop safety against maize and canola at the rate of 150 g ai/ha, indicating that II-13 might have potential as a herbicide for weed control in maize and canola fields. II-13 is the first HPPD inhibitor showing good crop safety toward canola.