Insertion of Small Flexible Linkers as a Useful Scaffold Hopping Tool in Agrochemistry

Rational design, synthesis and binding mechanisms of novel benzyl geranate derivatives as potential eco-friendly aphid repellents

BACKGROUND

The push-pull strategy is considered as a promising eco-friendly method for pest management. Plant volatile organic compounds (PVOCs) act as semiochemicals constitute the key factor in implementing this strategy. Benzyl alcohol and geraniol, as functional PVOCs, were reported to regulate insect behavior, showing the potential application in pest control. Using geraniol as lead, a geraniol derivative 5i with fine repellent activity was discovered in our previous work. In order to explore novel, eco-friendly aphid control agents, a series of benzyl geranate derivatives was designed and synthesized using 5i as the lead and benzyl alcohol as the active fragment.

RESULTS

Benzyl alcohol was firstly evaluated to have repellent activity to Acyrthosiphon pisum. Based on this repellent fragment, a series of novel benzyl geranate derivatives was rationally designed and synthesized using a scaffold-hopping strategy. Among them, compound T9, with a binding affinity (Kd  = 0.43 μm) and a substantial repellency of 64.7% against A. pisum, is the most promising compound. Molecule docking showed that hydrophobic and hydrogen-bonding interactions substantially influenced the binding affinity of compounds with ApisOBP9. Additionally, T9 exhibited low-toxicity to honeybees and ladybugs.

CONCLUSION

Using a simple scaffold-hopping strategy combined with active fragment benzyl alcohol, a new derivative T9, with high aphid-repellency and low-toxicity to nontarget organisms, can be considered as a novel potential eco-friendly aphid control agent for sustainable agriculture. © 2023 Society of Chemical Industry.

Isosteric Ring Exchange as a Useful Scaffold Hopping Tool in Agrochemistry

Replacing one ring in a molecule by a different carba- or heterocycle is an important scaffold hopping manipulation, because biologically active compounds and their analogues, which underwent such a transformation, are often similar in size, shape, and physicochemical properties and, therefore, likely in their potency as well. This review will demonstrate, how isosteric ring exchange led to the discovery of highly active agrochemicals and which ring interchanges have proven to be most successful.

Design, Synthesis, and Biological Evaluation of Novel Derivatives of the Marine Natural Product Laurene

Plant pathogenic fungi and viruses are seriously threatening agricultural production. There is an urgent need to develop novel fungicides and antiviral agents with low toxicity and high efficiency. In this study, we designed and synthesized 32 thiazole-, hydrazone-, and amide-containing derivatives of laurene and systematically evaluated their antiviral activities and fungicidal activities. Structure-simplified compounds 5a-5c, 5i, 5k, 5l, 11a, 11j, and 12c displayed higher antiviral activities than that of ningnanmycin. Compound 11a with a simple chemical structure, convenient synthetic route, and excellent antiviral activity emerged as a secondary lead compound. The docking results show that compounds 5i, 5k, and 11a have strong interactions with the tobacco mosaic virus coat protein (TMV CP). These compounds also exhibited significant fungicidal activities. Compounds 5g, 5k, 11j, and 11l displayed 9.15-17.45 μg/mL EC50 values against Pyricularia grisea, and compounds 5h (EC50: 8.01 μg/mL) and 11i (EC50: 15.23 μg/mL) exhibited a similar level of EC50 values with chlorothalonil (EC50: 7.33 μg/mL) against Physalospora piricola. Preliminary fungicidal mechanism research indicated that compound 5h has a certain destructive effect on the hyphae of P. piricola. This work lays a foundation for the application of laurene derivatives in plant protection.

A Potential Lead for Insect Growth Regulator: Design, Synthesis, and Biological Activity Evaluation of Novel Hexacyclic Pyrazolamide Derivatives

Ecdysone receptor (EcR) and chitinase play a critical role in the molting stage of insect pests. Each of them is considered a promising target for the development of novel insect growth regulators (IGRs). In the present paper, a total of 24 (23 novel) hexacyclic pyrazolamide derivatives were designed and synthesized by reducing the heptacycle and inserting small flexible linkers on the basis of the previously discovered dual-target compound D-27 acting simultaneously on EcR and Ostrinia furnacalis chitinase (OfChtI). Their insecticidal activities against Plutella xylostella, Spodoptera frugiperda, and Ostrinia furnacalis larvae were evaluated. The results revealed that the insecticidal activity was not significantly enhanced when the heptacycle on the pyrazole ring was reduced to a hexacycle. However, the insertion of an additional methylene spacer between the substituted phenyl ring and the amide bond can improve the insecticidal activity. Among the derivatives, the most potent compound, 6j, exhibited promising insecticidal activities against P. xylostella and S. frugiperda. Further protein binding assays and molecular docking indicated that 6j could target both EcR and OfChtI, and is a potential lead compound for IGRs. The present work provides valuable clues for the development of new dual-target IGRs.

Design, Synthesis, and Insecticidal and Fungicidal Activities of Ether/Oxime-ether Containing Isoxazoline Derivatives

The existing agricultural insecticides have developed drug resistance from long-term use. Isoxazoline derivatives are new insecticides discovered in the 21st century. Because of their unique insecticidal mechanism, high selectivity, safety, and no significant cross resistance with the existing pesticides on the market, they have become a hot spot in the field of pesticide research. Herein, a series of novel isoxazoline derivatives containing ether and oxime-ether structures were designed and synthesized by a scaffold-hopping strategy using the pesticide fluralaner as a template structure. Through the investigation of insecticidal activity and the systematic structure-activity relationship, a series of compounds with high insecticidal activities were found, and compounds I-4, II-9, and II-13 with LC₅₀ values of 0.00008-0.00036 mg/L against diamondback moth emerged as novel insecticide candidates. These compounds also exhibited broad spectrum fungicidal activities against 14 plant fungi. The current work provides a reference for the design of new isoxazoline compounds based on the scaffold-hopping strategy.

Design, Synthesis, Antiviral and Fungicidal Activities of Novel Polycarpine Simplified Analogues

Fungal and viral diseases account for 70-80% of agricultural production losses caused by microbial diseases. Synthetic fungicides and antiviral agents have been used to treat plant diseases caused by plant pathogenic fungi and viruses, but their use has been criticized due to their adverse side effects. As alternative strategies, natural fungicides and antiviral agents have attracted many researchers' interest in recent years. Herein, we designed and synthesized a series of novel polycarpine simplified analogues. Antiviral activity research against tobacco mosaic virus (TMV) revealed that most of the designed compounds have good antiviral activities. The virucidal activities of 4, 6d, 6f, 6h, and 8c are higher than that of polycarpine and similar to that of ningnanmycin. The structure simplified compound 8c was selected for further antiviral mechanism research which showed that compound 8c could inhibit the formation of 20S protein discs by acting on TMV coat protein. These compounds also displayed broad-spectrum fungicidal activities against 7 kinds of plant fungi. This work lays the foundation for the application of polycarpine simplified analogues in crop protection.

Bioisosterism and Scaffold Hopping in Modern Nematicide Research

The application of agrochemicals is critical to global food safety. Nowadays, environmentally friendly green agrochemicals are the trend in field crop protection. The research and development of nematicides absorbed more attention as a typical representation of agrochemicals. This review describes the origin of recently commercialized nematicides, the application of bioisosterism and scaffold hopping in the discovery and optimization of agrochemicals, especially nematicides, and novel bioisosteric design strategies for the identification of fluensulfone analogues. Pesticide repurposing, high-throughput screening, computer-aided drug design, and incorporation of known pharmacophoric fragments have been the most successful approach for the discovery of new nematicides. As outlined, the strategies of bioisosteric replacements and scaffold hopping have been very successful approaches in the search for new nematicides for sustainable crop protection. In the exploration of novel fluensulfone analogues with nematicidal activity, bioisosteric replacement of sulfone by amide, chain extension by insertion of a methylene group, and reversal of the amide group have proven to be successful approaches and yielded new and highly active fluensulfone analogues. These attempts might result in compounds with an optimal balance of steric, hydrophobic, electronic, and hydrogen-bonding properties and contribute to deal with the complex problem during the research and development of new nematicides. Further ideas are also put forward to provide new approaches for the molecular design of nematicides.