Pyrazolidine-3,5-dione-based inhibitors of phosphoenolpyruvate carboxylase as a new class of potential C4 plant herbicides

Discovery of novel Propionamide-Pyrazole-Carboxylates as Transketolase-inhibiting herbicidal candidates

BACKGROUND

Transketolase (TKL, EC 2.2.1.1) is a key enzyme in the pentose phosphate pathway and Calvin cycle, and is expected to act as a herbicidal site-of-action. On the basis of TKL, we designed and synthesized a series of 1-oxy-propionamide-pyrazole-3-carboxylate analogues and evaluated their herbicidal activities.

RESULTS

Methyl 1-methyl-5-((1-oxo-1-((4-(trifluoromethyl)phenyl)amino)propan-2-yl)oxy)-1H-pyrazole-3-carboxylate (C23) and methyl 1-methyl-5-((1-oxo-1-((perfluorophenyl)amino)propan-2-yl)oxy)-1H-pyrazole-3-carboxylate (C33) were found to provide better growth-inhibition activities against Digitaria sanguinalis root than those of nicosulfuron, mesotrione and pretilachlor at 200 mg L-1 using the small-cup method. These compounds were also identified as promising compounds in pre-emergence and postemergence herbicidal-activity experiments, with relatively good inhibitory effects toward Amaranthus retroflexus and D. sanguinalis at 150 g ai ha-1. In addition, enzyme inhibition assays and molecular docking studies revealed that C23 and C33 interact favourably with SvTKL (Setaria viridis TKL).

CONCLUSION

C23 and C33 are promising lead TKL inhibitors for the optimization of new herbicides. © 2024 Society of Chemical Industry.

Identification of ligands binding to MB327-PAM-1, a binding pocket relevant for resensitization of nAChRs

Desensitization of nicotinic acetylcholine receptors (nAChRs) can be induced by overstimulation with acetylcholine (ACh) caused by an insufficient degradation of ACh after poisoning with organophosphorus compounds (OPCs). Currently, there is no generally applicable treatment for OPC poisoning that directly targets the desensitized nAChR. The bispyridinium compound MB327, an allosteric modulator of nAChR, has been shown to act as a resensitizer of nAChRs, indicating that drugs binding directly to nAChRs can have beneficial effects after OPC poisoning. However, MB327 also acts as an inhibitor of nAChRs at higher concentrations and can thus not be used for OPC poisoning treatment. Consequently, novel, more potent resensitizers are required. To successfully design novel ligands, the knowledge of the binding site is of utmost importance. Recently, we performed in silico studies to identify a new potential binding site of MB327, MB327-PAM-1, for which a more affine ligand, UNC0646, has been described. In this work, we performed ligand-based screening approaches to identify novel analogs of UNC0646 to help further understand the structure-affinity relationship of this compound class. Furthermore, we used structure-based screenings and identified compounds representing four new chemotypes binding to MB327-PAM-1. One of these compounds, cycloguanil, is the active metabolite of the antimalaria drug proguanil and shows a higher affinity towards MB327-PAM-1 than MB327. Furthermore, cycloguanil can reestablish the muscle force in soman-inhibited rat muscles. These results can act as a starting point to develop more potent resensitizers of nAChR and to close the gap in the treatment after OPC poisoning.

Efficient In Vivo Screening Method for the Identification of C4 Photosynthesis Inhibitors Based on Cell Suspensions of the Single-Cell C4 Plant Bienertia sinuspersici

The identification of novel herbicides is of crucial importance to modern agriculture. We developed an efficient in vivo assay based on oxygen evolution measurements using suspensions of chlorenchyma cells isolated from the single-cell C₄ plant Bienertia sinuspersici to identify and characterize inhibitors of C₄ photosynthesis. This novel approach fills the gap between conventional in vitro assays for inhibitors targeting C₄ key enzymes and in vivo experiments on whole plants. The assay addresses inhibition of the target enzymes in a plant context thereby taking care of any reduced target inhibition due to metabolization or inadequate uptake of small molecule inhibitors across plant cell walls and membranes. Known small molecule inhibitors targeting C₄ photosynthesis were used to validate the approach. To this end, we tested pyruvate phosphate dikinase inhibitor bisindolylmaleimide IV and phosphoenolpyruvate carboxylase inhibitor okanin. Both inhibitors show inhibition of plant photosynthesis at half-maximal inhibitory concentrations in the sub-mM range and confirm their potential to act as a new class of C₄ selective inhibitors.