Designing New Protoporphyrinogen Oxidase-Inhibitors Carrying Potential Side Chain Isosteres to Enhance Crop Safety and Spectrum of Activity

Understanding the Effects of Ligand Configuration on Protoporphyrinogen IX Oxidase with Rationally Designed 3-(N-Phenyluracil)but-2-enoates

Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is a promising target for green herbicide discovery. However, the ligand configuration effects on PPO activity were still poorly understood. Herein, we designed 3-(N-phenyluracil)but-2-enoates using our previously developed active fragments exchange and link (AFEL) approach and synthesized a series of novel compounds with nanomolar ranges of Nicotiana tabacum PPO (NtPPO) inhibitory potency and promising herbicidal potency. Our systematic structure-activity relationship investigations showed that the E isomers of 3-(N-phenyluracil)but-2-enoates displayed improved bioactivity than their corresponding Z isomers. Using molecular simulation studies, we found that the E isomers showed a relatively lower entropy change and could sample more stable binding conformation to the receptor than the Z isomers. Our density functional theory (DFT) calculations showed that the E isomers showed higher chemical reactivity and lower electronic chemical potential than their corresponding Z isomers. Compound E-Ic emerged as the optimal compound with a Ki value of 3.0 nM against NtPPO, exhibiting a broader spectrum of weed control than saflufenacil at 37.5-75 g ai/ha and also safe to maize at 75 g ai/ha, which could be considered as a promising lead herbicide for further development.

Design, Synthesis, and Bioactivities of N-Heterocyclic Ureas as Strigolactone Response Antagonists against Parasitic-Weed Seed Germination

The pernicious parasitism exhibited by root parasitic weeds such as Orobanche and Striga poses substantial peril to agricultural productivity and global food security. This deleterious phenomenon hinges upon the targeted induction of the signaling molecule strigolactones (SLs). Consequently, the identification of prospective SL antagonists holds significant promise in the realm of mitigating the infection of these pernicious weeds. In this study, we synthesized and characterized D12 based on a potent SL antagonist KK094. In vivo assay results demonstrated that D12 remarkably impedes the germination of Phelipanche aegyptiaca and Striga asiatica seeds, while also alleviating the inhibitory consequence of the SL analogue GR24 on hypocotyl elongation in Arabidopsis thaliana. The docking study and ITC assay indicated that D12 can interact strongly with the SL receptor protein, which may interfere with the binding of SL to the receptor protein as a result. In addition, the results of crop safety assessment tests showed that D12 had no adverse effects on rice seed germination and seedling growth and development. The outcomes obtained from the present study suggested that D12 exhibited promise as a prospective antagonist of SL receptors, thereby displaying substantial efficacy in impeding the seed germination process of root parasitic weeds, providing a promising basis for rational design and development of further Striga-specific herbicides.

Discovery and optimization of spirocyclic lactams that inhibit acyl-ACP thioesterase

BACKGROUND

There are various methods to control weeds, that represent considerable challenges for farmers around the globe, although applying small molecular compounds is still the most effective and versatile technology to date. In the search for novel chemical entities with new modes-of-action that can control weeds displaying resistance, we have investigated two spirocyclic classes of acyl-ACP thioesterase inhibitors based on X-ray co-crystal structures and subsequent modelling studies.

RESULTS

By exploiting scaffold-hopping and isostere concepts, we were able to identify new spirolactam-based lead structures showing promising activity in vivo against commercially important grass weeds in line with strong target affinity.

CONCLUSION

The present work covers a series of novel herbicidal lead structures that contain a spirocyclic lactam as a structural key feature carrying ortho-substituted benzyl or heteroarylmethylene side chains. These new compounds show good acyl-ACP thioesterase inhibition in line with strong herbicidal activity. Glasshouse trials showed that the spirolactams outlined herein display promising control of grass-weed species in pre-emergence application combined with dose-response windows that enable partial selectivity in wheat and corn. Remarkably, some of the novel acyl-ACP thioesterase-inhibitors showed efficacy against resistant grass weeds such as Alopecurus myosuroides and Lolium spp. on competitive levels compared with commercial standards. © 2024 Society of Chemical Industry.

Design, Synthesis, and Herbicidal Activity of Substituted 3-(Pyridin-2-yl)Phenylamino Derivatives

To discover protoporphyrinogen oxidase (PPO) inhibitors with robust herbicidal activity and crop safety, three types of substituted 3-(pyridin-2-yl)phenylamino derivatives bearing amide, urea, or thiourea as side chain were designed via structure splicing strategy. Postemergence herbicidal activity assessment of 33 newly prepared compounds revealed that many of our compounds such as 6a, 7b, and 8d exhibited superior herbicidal activities against broadleaf and monocotyledon weeds to commercial acifluorfen. In particular, compound 8d exhibited excellent herbicidal activities and high crop safety at a dosage range of 37.5-150 g ai/ha. PPO inhibitory studies supported our compounds as typical PPO inhibitors. Molecular docking studies revealed that compound 8d provided effective interactions with Nicotiana tabacum PPO (NtPPO) via diverse interaction models, such as π-π stacking and hydrogen bonds. Molecular dynamics (MD) simulation studies and degradation studies were also conducted to gain insight into the inhibitory mechanism. Our study indicates that compound 8d may be a candidate molecule for the development of novel herbicides.