Structure-Based Virtual Screening of Natural Products and Optimization for the Design and Synthesis of Novel CeCht1 Inhibitors as Nematicide Candidates

A Novel Peptidomimetic Insecticide: Dippu-AstR-Based Rational Design and Biological Activity of Allatostatin Analogs

Insect neuropeptides play an essential role in regulating growth, development, reproduction, nerve conduction, metabolism, and behavior in insects; therefore, G protein-coupled receptors of neuropeptides are considered important targets for designing green insecticides. Cockroach-type allatostatins (ASTs) (FGLamides allatostatins) are important insect neuropeptides in Diploptera punctata that inhibit juvenile hormone (JH) synthesis in the corpora allata and affect growth, development, and reproduction of insects. Therefore, the pursuit of novel insecticides targeting the allatostatin receptor (AstR) holds significant importance. Previously, we identified an AST analogue, H17, as a promising candidate for pest control. Herein, we first modeled the 3D structure of AstR in D. punctata (Dippu-AstR) and predicted the binding mode of H17 with Dippu-AstR to study the critical interactions and residues favorable to its bioactivity. Based on this binding mode, we designed and synthesized a series of H17 derivatives and assessed their insecticidal activity against D. punctata. Among them, compound Q6 showed higher insecticidal activity than H17 against D. punctata by inhibiting JH biosynthesis, indicating that Q6 is a potential candidate for a novel insect growth regulator (IGR)-based insecticide. Moreover, Q6 exhibited insecticidal activity against Plutella xylostella, indicating that these AST analogs may have a wider insecticidal spectrum. The underlying mechanisms and molecular conformations mediating the interactions of Q6 with Dippu-AstR were explored to understand its effects on the bioactivity. The present work clarifies how a target-based strategy facilitates the discovery of new peptide mimics with better bioactivity, enabling improved IGR-based insecticide potency in sustainable agriculture.

Structure-Based Virtual Screening, ADMET Properties Prediction and Molecular Dynamics Studies Reveal Potential Inhibitors of Mycoplasma pneumoniae HPrK/P

Mycoplasma pneumoniae pneumonia (MPP) is a frequent cause of community-acquired pneumonia (CAP) in children. The incidence of childhood pneumonia caused by M. pneumoniae infection has been rapidly increasing worldwide. M. pneumoniae is naturally resistant to beta-lactam antibiotics due to its lack of a cell wall. Macrolides and related antibiotics are considered the optimal drugs for treating M. pneumoniae infection. However, clinical resistance to macrolides has become a global concern in recent years. Therefore, it is imperative to urgently identify new targets and develop new anti-M. pneumoniae drugs to treat MMP. Previous studies have shown that deficiencies in HPrK/P kinase or phosphorylase activity can seriously affect carbon metabolism, growth, morphology, and other cellular functions of M. pneumoniae. To identify potential drug development targets against M. pneumoniae, this study analyzed the sequence homology and 3D structure alignment of M. pneumoniae HPrK/P. Through sequence and structure analysis, we found that HPrK/P lacks homologous proteins in the human, while its functional motifs are highly conserved in bacteria. This renders it a promising candidate for drug development. Structure-based virtual screening was then used to discover potential inhibitors among 2614 FDA-approved drugs and 948 bioactive small molecules for M. pneumoniae HPrK/P. Finally, we identified three candidate drugs (Folic acid, Protokylol and Gluconolactone) as potential HPrK/P inhibitors through molecular docking, molecular dynamics (MDs) simulations, and ADMET predictions. These drugs offer new strategies for the treatment of MPP.

A Potential Multitarget Insect Growth Regulator Candidate: Design, Synthesis, and Biological Activity of Novel Acetamido Derivatives Containing Hexacyclic Pyrazole Carboxamides

Insect growth regulators (IGRs) are important green insecticides that disrupt normal growth and development in insects to reduce the harm caused by pests to crops. The ecdysone receptor (EcR) and three chitinases OfChtI, OfChtII, and OfChi-h are closely associated with the molting stage of insects. Thus, they are considered promising targets for the development of novel insecticides such as IGRs. Our previous work identified a dual-target compound 6j, which could act simultaneously on both EcR and OfChtI. In the present study, 6j was first found to have inhibitory activities against OfChtII and OfChi-h, too. Subsequently, taking 6j as a lead compound, 19 novel acetamido derivatives were rationally designed and synthesized by introducing an acetamido moiety into the amide bridge based on the flexibility of the binding cavities of 6j with EcR and three chitinases. Then, their insecticidal activities against Plutella xylostella (P. xylostella), Ostrinia furnacalis (O. furnacalis), and Spodoptera frugiperda (S. frugiperda) were carried out. The bioassay results revealed that most of these acetamido derivatives possessed moderate to good larvicidal activities against three lepidopteran pests. Especially, compound I-17 displayed excellent insecticidal activities against P. xylostella (LC50, 93.32 mg/L), O. furnacalis (LC50, 114.79 mg/L), and S. frugiperda (86.1% mortality at 500 mg/L), significantly better than that of 6j. In addition, further protein validation and molecular docking demonstrated that I-17 could act simultaneously on EcR (17.7% binding activity at 8 mg/L), OfChtI (69.2% inhibitory rate at 50 μM), OfChtII (71.5% inhibitory rate at 50 μM), and OfChi-h (73.9% inhibitory rate at 50 μM), indicating that I-17 is a potential lead candidate for novel multitarget IGRs. This work provides a promising starting point for the development of novel types of IGRs as pest management agents.

Novel 5-Sulfonyl-1,3,4-thiadiazole-Substituted Flavonoids as Potential Bactericides and Fungicides: Design, Synthesis, Three-Dimensional Quantitative Structure-Activity Relationship Studies

Flavonoids, ubiquitous natural products, provide sources for drug discovery owing to their structural diversity, broad-spectrum pharmacological activity, and excellent environmental compatibility. To develop antibacterial and antifungal agents with novel mechanisms of action and innovative structures, a series of novel 5-sulfonyl-1,3,4-thiadiazole-substituted flavonoids were designed and synthesized, and their biological activities against seven agriculturally common phytopathogenic microorganisms were evaluated. The results of the antimicrobial bioassay showed that most of the target compounds displayed excellent inhibitory effects against Xanthomonas oryzae, Rhizoctonia solani, and Colletotrichum orbiculare. Compounds 1, 3, 7, 9, 13, and 14 exhibited remarkable antibacterial activity against X. oryzae pv. oryzae with EC50 values below 10 μg/mL, which were superior to bismerthiazol (70.89 μg/mL). Compound 2 (EC50 = 0.41 μg/mL) displayed the most effective inhibitory potency against R. solani in vivo, comparable protective effects with the positive control carbendizam. Preliminary mechanistic studies indicated that compound 2 induced disordered entanglement of hyphae, shrinkage of hyphal surfaces, extravasation of cellular contents, and vacuole swelling and rupture, which disrupted normal hyphal growth. Subsequently, compounds 35-53 with good antifungal activity were designed and synthesized based on reliable three-dimensional quantitative structure-activity relationship (3D-QSAR) models. Compound 49 showed high efficacy and superior antifungal activity against R. solani, with an EC50 value of 0.28 μg/mL and a half-maximal effective concentration of 0.46 μg/mL.

Target-Based Design, Synthesis, and Biological Evaluation of Novel 1,2,4-Triazolone Derivatives as Potential nAChR Modulators

Novel agrochemicals have been successfully developed using target-based drug design (TBDD). To discover a novel, efficient, and highly selective nicotinic insecticide candidate, we developed a unified pharmacological model using TBDD by studying the binding modes of 11 nicotinic acetylcholine receptor (nAChR) modulators with acetylcholine binding protein (AChBP) targets for the first time. This model was used to design and develop a series of 1,2,4-triazolone derivatives. Bioassays demonstrated excellent insecticidal activities against Aphis glycines of compounds 4k (LC50 = 4.95 mg/L) and 4q (LC50 = 3.17 mg/L), and low toxicities to Apis mellifera. Additionally, compound 4q was stably bound to Aplysia californica AChBP, which was consistent with the pharmacological model obtained via molecular docking and molecular dynamics simulations. Therefore, compound 4q could be a potential lead candidate targeting nAChR. The explicit pharmacological model of nAChR modulators with Ac-AChBP in this study may facilitate the future rational design of eco-friendly nicotinic insecticides.

Synthesis, Nematicidal Evaluation, and the Structure-Activity Relationship Study of Aurone Derivatives

Plant-parasitic nematodes (PPNs) are one of the major threats to modern agriculture. Chemical nematicides are still required for the management of PPNs. Based on our previous work, the structure of aurone analogues was obtained using a hybrid 3D similarity calculation method (SHAFTS, SHApe-FeaTure Similarity). Thirty-seven compounds were synthesized. The nematicidal activity of target compounds against Meloidogyne incognita (root-knot nematode, M. incognita) was evaluated, and the structure-activity relationship of synthesized compounds was analyzed. The results showed that compound 6 and some of its derivatives exhibited impressive nematicidal activity. Among these compounds, compound 32 bearing 6-F showed the best in vitro and in vivo nematicidal activity. Its lethal concentration 50% after exposure to 72 h (LC_50/72 h) value was 1.75 mg/L, and the inhibition rate reached 97.93% in the sand at 40 mg/L. At the same time, compound 32 also exhibited excellent inhibition on egg hatching and moderate inhibition on the motility of Caenorhabditis elegans (C. elegans).