A Study in Scaffold Hopping: Discovery and Optimization of Thiazolopyridines as Potent Herbicides That Inhibit Acyl-ACP Thioesterase

Synthesis and biological profile of substituted hexahydrofuro[3,4-b]furans, a novel class of bicyclic acyl-acyl carrier protein (ACP) thioesterase inhibitors

BACKGROUND

Weed control is a significant challenge for farmers around the globe. Of the various methods available for combatting weeds, small molecules remain the most effective and versatile technology to date. In the search for novel chemical entities with new modes of action toward herbicide-resistant weeds, we have investigated hexahydrofuro[3,4-b]furan-based acyl-acyl carrier protein (ACP) thioesterase inhibitors inspired by X-ray co-crystal structure-based modeling studies.

RESULTS

By exploiting scaffold hopping concepts and molecular modeling studies we were able to identify new hexahydrofuro[3,4-b]furan-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 possess a hexahydrofuro[3,4-b]furan scaffold as a structural key feature, carrying ortho-substituted aryloxy side chains. Based on an optimized synthetic approach a broad structure-activity relationship (SAR) study was carried out. The new compounds emerging from our modeling-inspired structural variations show good acyl-ACP thioesterase inhibition in line with promising initial herbicidal activity. Glasshouse trials showed that the hexahydrofuro[3,4-b]furans outlined herein display good control of cold and warm season grass-weed species in pre-emergence application. Remarkably, some of the novel acyl-ACP thioesterase-inhibitors also showed promising efficacy against warm season weeds that are difficult to control. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Investigation of acetyl-CoA carboxylase-inhibiting herbicides that exhibit soybean crop selectivity

The sustainable control of weed populations, particularly resistant species, is a significant challenge in agriculture around the world. The α-aryl-keto-enol (aryl-KTE) class of acetyl-CoA carboxylase (ACCase)-inhibiting herbicides represent a possible solution for the control of resistant grasses even though achieving crop selectivity remains a challenge. Herein, we present some of our investigations into identifying the most promising structural features within the aryl-KTE class that give the highest chance of achieving soybean crop selectivity, whilst also maintaining strong and broad efficacy against problematic weed species. We further examined our results by preparing new aryl-KTE molecules which were evaluated in glasshouse screening assays for their herbicidal efficacy as well as their soybean selectivity. We consider that uniting this approach with other optimization criteria, such as toxicological and environmental safety profiles, will enable the streamlining of crop protection optimizations programmes, ultimately delivering safer and more sustainable solutions to farmers and consumers. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Scaffold hopping approaches for the exploration of herbicidally active compounds inhibiting Acyl-ACP Thioesterase

BACKGROUND

The sustainable control of weed populations is a significant challenge facing farmers around the world. Although various methods for the control of weeds exist, the use of small molecule herbicides remains the most effective and versatile approach. Striving to find novel herbicides that combat resistant weeds via the targeting of plant specific modes of action (MoAs), we further investigated the bicyclic class of acyl-acyl carrier protein (ACP) thioesterase (FAT) inhibitors in an effort to find safe and efficacious lead candidates.

RESULTS

Utilizing scaffold hopping and bioisosteric replacements strategies, we explored new bicyclic inhibitors of FAT. Amongst the investigated compounds we identified new structural motifs that showed promising target affinity coupled with good in vivo efficacy against commercially important weed species. We further studied the structure-activity relationship (SAR) of the novel dihydropyranopyridine structural class which showed promise as a new type of FAT inhibiting herbicides.

CONCLUSION

The current work presents how scaffold hopping approaches can be implemented to successfully find novel and efficacious herbicidal structures that can be further optimized for potential use in sustainable agricultural practices. The identified dihydropyranopyridine bicyclic class of herbicides were demonstrated to have in vitro inhibitory activity against the plant specific MoA FAT as well as showing promising control of a variety of weed species, particularly grass weeds in greenhouse trials on levels competitive with commercial standards. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Aminoisothiazolamides, a new class of potent inhibitors of lysyl-tRNA synthetase

BACKGROUND

Owing to the economic relevance of resistance evolution against herbicides, new chemical entities addressing unprecedented molecular targets are urgently needed to develop future sustainable weed control solutions. As part of our discovery research, the new class of aminoisothiazolamides was investigated.

RESULTS

Aminoisothiazolamide 3-amino-4-chloro-N-(cyclohexylmethyl)isothiazole-5-carboxamide 1a and several of its derivatives displayed potent herbicidal and fungicidal in vivo activity in initial glasshouse tests. Lysyl-tRNA synthetase 1 (KRS1) was identified as the putative target for 1a and was validated as a key contributor to the biochemical mode-of-action of aminoisothiazolamides. Thermal stability shift analysis with KRS1 from Arabidopsis thaliana (AtKRS1) revealed that 1a specifically increased the thermostability of this enzyme, proving the KRS1 enzyme as the aminoisothiazolamide target. It turned out that the inhibition of AtKRS1 and HsKRS was strongly correlated, as was the inhibition of AtKRS1 and the herbicidal activity of the aminoisothiazolamides. Hence, in vivo acute toxicity tests were initiated at a very early project stage complementing the enzyme tests.

CONCLUSION

The observed toxicological effects paired with the anticipated likelihood to overcome this problem, owing to the highly conserved active sites in different species, finally resulted in the conclusion to stop the further exploration of the otherwise promising class of herbicidal aminoisothiazolamides. Thus, we opted to discard several further herbicidal lead structures before the start of in-depth investigations when sequence analyses suggested similar levels of conservation between the respective binding pockets in plants and mammalians. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Design, synthesis, crystal structure, fungicidal activity, and mechanism of action of novel thiazole-based hydrazide derivatives containing the 4-aminoquinazoline moiety

A family of novel thiazole-based hydrazide derivatives bearing the 4-aminoquinazoline moiety were designed and synthesized by the molecular hybridization strategy, and assessed for their antifungal activities in vitro and in vivo. Among these derivatives, the chemical structure of compound A26 was clearly confirmed via X-ray crystallography. The bioassay results revealed that some of the synthesized compounds exhibited significant inhibition effects against the tested phytopathogenic fungi. For example, in vitro EC50 (half maximal effective concentration) values of compounds A19 and A26 against Rhizoctonia solani, A19 against Verticillium dahliae, A26 against Alternaria solani, and A17 against Colletotrichum gloeosporioides were all less than 3.0 μg/mL. In particular, compound A19 with a 2-fluorophenyl group had an EC50 value as low as 2.87 μg/mL towards R. solani, comparable to that of Chlorothalonil (1.44 μg/mL) and slightly inferior to those of Carbendazim and Boscalid (0.85 and 0.83 μg/mL, respectively). In addition, in vivo assays using this compound displayed the curative and protective efficiencies of 48.4% and 59.6% against R. solani, respectively, at the concentration of 200 μg/mL. Moreover, the mechanistic studies indicated that compound A19 likely exerted its highly antifungal effects by acting as an effective succinate dehydrogenase (SDH) inhibitor with an IC50 value of 29.33 μM, based on SDH enzymatic inhibition assays and molecular docking studies. Meanwhile, the presence of compound A19 adversely impacted the integrity of cell membranes and mycelial morphologies of R. solani.

Thiazole and Isothiazole Chemistry in Crop Protection

Thiazole and isothiazole are types of five-membered heterocycles that contain both sulfur and nitrogen atoms. They have gained attention in the field of green pesticide research due to their low toxicity, strong biological activity, and ability to undergo diverse structural modifications. By incorporating thiazole and isothiazole groups into various compounds, researchers have been able to create a wide range of pesticides with broad-spectrum effectiveness. Understanding the relationship between the structure of these compounds and their activities is crucial for the development of new and highly potent pesticides. This review highlights thiazole and isothiazole derivatives with various biological activities and aims to inspire the development of innovative pesticide based on these structures.

Synthesis and biological profile of 2,3-dihydro[1,3]thiazolo[4,5-b]pyridines, a novel class of acyl-ACP thioesterase inhibitors

The present work covers novel herbicidal lead structures that contain a 2,3-dihydro[1,3]thiazolo[4,5-b]pyridine scaffold as structural key feature carrying a substituted phenyl side chain. These new compounds show good acyl-ACP thioesterase inhibition in line with strong herbicidal activity against commercially important weeds in broadacre crops, e.g., wheat and corn. The desired substituted 2,3-dihydro[1,3]thiazolo[4,5-b]pyridines were prepared via an optimized BH3-mediated reduction involving tris(pentafluorophenyl)borane as a strong Lewis acid. Remarkably, greenhouse trials showed that some of the target compounds outlined herein display promising control of grass weed species in preemergence application, combined with a dose response window that enables partial selectivity in certain crops.