Silicon-Containing Complex II Acaricides─Design, Synthesis, and Pharmacological Optimization

Novel Insecticidal Benzo[4,5]imidazo[1,2-b]pyrazole Derivatives Idenatified Through Ring-Closure Scaffold Hopping on Fipronil

A series of innovative benzo[4,5]imidazo[1,2-b]pyrazole scaffold containing compounds were rationally designed through a ring-closure scaffold hopping strategy and synthetized with an intermediate derivatization approach. Physicochemical properties analysis indicated the potential pesticide-likeness of the target compounds. The optimal target compound A14 showed relatively good insecticidal activity against P. xylostella, with an LC50 value of 37.58 mg/L, and demonstrated lower acute fish toxicity compared to fipronil. Docking binding mode analysis demonstrated that compound A14 bound to GABAR through a H-bond between the amide group and the residue of 6'Thr. The differences in binding modes between benzo[4,5]imidazo[1,2-b]pyrazole target compounds and fipronil may be a key factor for the reduced insecticidal activities. The elucidated binding mode and SAR profile lay a foundation for the further structural optimization of insecticidal benzo[4,5]imidazo[1,2-b]pyrazole derivatives.

Cu(I)-Catalyzed Silylation and Germylation of Azauracils

The current study demonstrates a Cu(I) catalyzed direct C(sp2)-H silylation and germylation of azauracil using triphenylsilane and triphenylgermane. A broad scope, excellent functional group tolerance, and suitability for large-scale reactions are exhibited in this protocol. Moreover, this method can be readily applied to structurally complex bioactive molecules. Experimental results suggest a radical mechanistic pathway for the reaction.

Organophotocatalytic Regioselective Silylation/Germylation and Cascade Cyclization of N-Alkenyl α-CF3 Acrylamides: Access to Densely Functionalized 4-Pyrrolin-2-ones

We report an organophotoredox-catalyzed silylation/germylation cascade cyclization of N-alkenyl α-CF3 acrylamides under mild conditions. N-Aminopyridinium salts act as hydrogen atom transfer reagents under photoredox catalysis in the generation of silyl and germyl radicals. An array of silyl- and germyl-substituted 3-CF3-4-pyrrolin-2-one derivatives were constructed in a shorter reaction time with low catalyst loading in good to excellent yields at room temperature. Importantly, this protocol is amenable to the late-stage diversification of bioactive molecules, as well as to large-scale synthesis.

Design, Synthesis, and Biological Activity of Silicon-Containing Carboxamide Fungicides

Bioisosteric silicon replacement has proven to be a valuable strategy in the design of bioactive molecules for crop protection and drug development. Twenty-one novel carboxamides possessing a silicon-containing biphenyl moiety were synthesized and tested for their antifungal activity and succinate dehydrogenase (SDH) enzymatic inhibitory activity. Among these novel succinate dehydrogenase inhibitors (SDHIs), compounds 3a, 3e, 4l, and 4o possessing appropriate clog P and topological polar surface area values showed excellent inhibitory effects against Rhizoctonia solani, Sclerotinia sclerotiorum, Botrytis cinerea, and Fusarium graminearum at 10 mg/L in vitro, and the EC50 values of 4l and 4o were 0.52 and 0.16 mg/L against R. solani and 0.066 and 0.054 mg/L against S. sclerotiorum, respectively, which were superior to those of Boscalid. Moreover, compound 3a demonstrated superior SDH enzymatic inhibitory activity (IC50 = 8.70 mg/L), exhibiting 2.54-fold the potency of Boscalid (IC50 = 22.09 mg/L). Docking results and scanning electron microscope experiments revealed similar mode of action between compound 3a and Boscalid. The new silicon-containing carboxamide 3a is a promising SDHI candidate that deserves further investigation.

Design, Synthesis, and Antifungal Activities of Novel Potent Fluoroalkenyl Succinate Dehydrogenase Inhibitors

The development of new fungicide molecules is a crucial task for agricultural chemists to enhance the effectiveness of fungicides in agricultural production. In this study, a series of novel fluoroalkenyl modified succinate dehydrogenase inhibitors were synthesized and evaluated for their antifungal activities against eight fungi. The results from the in vitro antifungal assay demonstrated that compound 34 exhibited superior activity against Rhizoctonia solani with an EC50 value of 0.04 μM, outperforming commercial fluxapyroxad (EC50 = 0.18 μM) and boscalid (EC50 = 3.07 μM). Furthermore, compound 34 showed similar effects to fluxapyroxad on other pathogenic fungi such as Sclerotinia sclerotiorum (EC50 = 1.13 μM), Monilinia fructicola (EC50 = 1.61 μM), Botrytis cinerea (EC50 = 1.21 μM), and also demonstrated protective and curative efficacies in vivo on rapeseed leaves and tomato fruits. Enzyme activity experiments and protein-ligand interaction analysis by surface plasmon resonance revealed that compound 34 had a stronger inhibitory effect on succinate dehydrogenase compared to fluxapyroxad. Additionally, molecular docking and DFT calculation confirmed that the fluoroalkenyl unit in compound 34 could enhance its binding capacity with the target protein through p-π conjugation and hydrogen bond interactions.

Photoredox Synthesis of Silicon-Containing Isoindolin-1-ones and Deuterated Analogues Through Hydrosilylation and Deuterium-silylation

An efficient, practical, and metal-free protocol for the synthesis of silicon-containing isoindolin-1-ones and deuterated analogues via the synergistic combination of an organic photoredox and hydrogen atom transfer process is described. This strategy features mild reaction conditions, high atom economy, and excellent functional group compatibility, delivering a myriad of structurally diverse and valuable products with good to excellent yields.

Discovery of new N-Phenylamide Isoxazoline derivatives with high insecticidal activity and reduced honeybee toxicity

Isoxazoline is a novel structure with strong potential for controlling agricultural insect pests, but its high toxicity to honeybees limits its development in agriculture. Herein, a series of N-phenylamide isoxazoline derivatives with low honeybee toxicity were designed and synthesized using the intermediate derivatization method. Bioassay results showed that these compounds exhibited good insecticidal activity. Compounds 3b and 3f showed significant insecticidal effects against Plutella xylostella (P. xylostella) with median lethal concentrations (LC50) of 0.06 and 0.07 mg/L, respectively, comparable to that of fluralaner (LC50 = 0.02 mg/L) and exceeding that of commercial insecticide fluxametamide (LC50 = 0.52 mg/L). It is noteworthy that the acute honeybee toxicities of compounds 3b and 3f (LD50 = 1.43 and 1.63 μg/adult, respectively) were significantly reduced to 1/10 of that of fluralaner (LD50 = 0.14 μg/adult), and were adequate or lower than that of fluxametamide (LD50 = 1.14 μg/adult). Theoretical simulation using molecular docking indicates that compound 3b has similar binding modes with fluralaner and a similar optimal docking pose with fluxametamide when binding to the GABA receptor, which may contribute to its potent insecticidal activity and relatively low toxicity to honey bees. This study provides compounds 3b and 3f as potential new insecticide candidates and provides insights into the development of new isoxazoline insecticides exhibiting both high efficacy and environmental safety.

Synthesis and Biological Activity of Silicon-Containing Ethylsulfonylpyridine Insecticides

Ethylsulfonylpyridines are a novel chemical class of insecticides with excellent broad-spectrum activity and an unprecedented mode of action. With the objective of discovering novel ethylsulfonylpyridines with a broader spectrum, wider range of uses, and/or improved properties, we have started a research program aimed at introducing silicon motifs and studying their biological effects. We designed a series of Oxazosulfyl analogues where the hydrogen atom at the 5-position of the pyridyl moiety is replaced by a trialkylsilyl group and prepared these compounds applying denovo synthetic methodology. Our novel ethylsulfonylpyridines exhibit excellent insecticidal activities. The best compound, A18, resulting from our research exhibited an LC50 value of 0.30 mg/L against Plutella xylostella and reached the activity level of the commercial standard Oxazosulfyl. Our findings confirmed our working hypothesis that at the 5-position of the pyridyl moiety larger groups with different hydrophobic, electronic, and steric properties are tolerated.

Novel Acaricidal Silico-Containing Pyrazolyl Acrylonitrile Derivatives Identified through Rational Carbon-Silicon Bioisosteric Replacement Strategy

The identification of novel pyrazolyl acrylonitrile acaricides with improved properties is of great value for the control of phytophagous mites. A series of innovative silicon-containing pyrazolyl acrylonitriles were rationally designed by applying a bioisosteric carbon-silicon replacement strategy and prepared based on novel synthetic methodology. As a result of our research, we discovered compound A25 which possesses outstanding acaricidal activity. With an LC50 value of 0.062 mg/L, compound A25 was found to be 2.3-fold and 1.9-fold more potent than the commercial acaricides cyenopyrafen and cyetpyrafen, respectively. Enzymatic inhibitory assay indicated that the active principle M1 of compound A25 possesses an IC50 value of 2.32 μM against Tetranychus cinnabarinus SDH, which was about twofold superior compared to the active metabolites of cyenopyrafen (IC50 = 4.72 μM). Molecular docking study showed that the active metabolites 2 and 3 and their corresponding silicon counterparts form H-bonds and cation-π interaction with the residues of Trp165, Tyr433, and Arg279.

Design, Synthesis, and Properties of Silicon-Containing meta-Diamide Insecticides

Silicon-containing compounds are sporadically used in crop protection and drug discovery and have demonstrated to increase the biological efficacy as well as to reduce toxicity, improve physicochemical properties, and favorably impact the environmental profile. As part of our research, we have investigated the application of bioisosteric silicon replacements in meta-diamide insecticides and studied the biological activity and molecular properties of the corresponding novel compounds. At all meaningful structural elements of the meta-diamides, silicon-containing substituents were introduced and synthetic methodology was developed for their syntheses. As the most promising compound, silicon-containing meta-diamide II-18 emerged, which exhibits a very low LC50 value of 2.00 mg/L against Mythimna separata and compares well to the reference compounds 28 (LC50 = 0.17 mg/L) and II-20 (LC50 = 0.27 mg/L). Our research on silicon-containing crop protection compounds once again confirmed that the biological activity can be beneficially affected by the insertion of silicone substituents and that the introduction of well-chosen silicone motifs is an excellent strategy for agrochemical research.

Lithium Triethylborohydride (LiHBEt3)-Promoted Hydrosilylation of Allenes to Prepare (E)-Allylsilanes

A transition-metal-free hydrosilylation of allenes is reported herein by using commercially available lithium triethylborohydride (LiHBEt3) as the catalyst. Both mono- and disubstituted allenes could be hydrosilylated with primary or secondary silanes effectively. This reaction represents an environmental and economic method to prepare (E)-allylsilanes in good yields along with decent selectivities.

Silicon switch: Carbon-silicon Bioisosteric replacement as a strategy to modulate the selectivity, physicochemical, and drug-like properties in anticancer pharmacophores

Bioisosterism is one of the leading strategies in medicinal chemistry for the design and modification of drugs, consisting in replacing an atom or a substituent with a different atom or a group with similar chemical properties and an inherent biocompatibility. The objective of such an exercise is to produce a diversity of molecules with similar behavior while enhancing the desire biological and pharmacological properties, without inducing significant changes to the chemical framework. In drug discovery and development, the optimization of the absorption, distribution, metabolism, elimination, and toxicity (ADMETox) profile is of paramount importance. Silicon appears to be the right choice as a carbon isostere because they possess very similar intrinsic properties. However, the replacement of a carbon by a silicon atom in pharmaceuticals has proven to result in improved efficacy and selectivity, while enhancing physicochemical properties and bioavailability. The current review discusses how silicon has been strategically introduced to modulate drug-like properties of anticancer agents, from a molecular design strategy, biological activity, computational modeling, and structure-activity relationships perspectives.

New 3-Aminopropylsilatrane Derivatives: Synthesis, Structure, Properties, and Biological Activity

The biologically active compound 3-aminopropylsilatrane (a compound with a pentacoordinated silicon atom) underwent an aza-Michael reaction with various acrylates and other Michael acceptors. Depending on the molar ratio, the reaction yielded Michael mono- or diadducts (11 examples) containing functional groups (silatranyl, carbonyl, nitrile, amino, etc.). These compounds were characterized via IR and NMR spectroscopy, mass spectrometry, X-ray diffraction, and elemental analysis. Calculations (using in silico, PASS, and SwissADMET online software) revealed that the functionalized (hybrid) silatranes were bioavailable, druglike compounds that exhibited pronounced antineoplastic and macrophage-colony-stimulating activity. The in vitro effect of silatranes on the growth of pathogenic bacteria (Listeria, Staphylococcus, and Yersinia) was studied. It was found that the synthesized compounds exerted inhibitory and stimulating effects in high and low concentrations, respectively.

Rational Exploration of Novel SDHI Fungicide through an Amide-β-ketonitrile Bioisosteric Replacement Strategy

The identification of succinate dehydrogenase inhibitor (SDHI) fungicides bearing a novel scaffold is of great importance to control pathogenic fungi. Difluoromethyl-pyrazole β-ketonitrile derivatives were rationally designed through an innovative amide-β-ketonitrile bioisosteric replacement strategy and evaluated for their antifungal activities. In preliminary fungicidal screening, our new β-ketonitrile compounds showed outstanding in vitro activity. Compounds A7 and A14 exhibited EC₅₀ values of 0.116 and 0.165 μg/mL against Sclerotinia sclerotiorum, respectively, and A14 also displayed an EC₅₀ of 0.0774 μg/mL against Rhizoctonia solani. Furthermore, A14 exhibited moderate in vivo protective activity against rice sheath blight on rice plants. Results from SDH enzymatic assays demonstrated that A14 possesses significant inhibitory effect toward porcine heart SDH, with an IC₅₀ value of 0.183 μM, which was 20-fold more potent than that of fluxapyroxad (IC₅₀ = 3.76 μM). A docking study indicated that H-bonds, cation-π interactions, and edge-to-face π-π interactions play key roles in the binding of A14 with R. solani SDH. The CoMSIA model guided the approach to further structural optimizations and indicated that hydrophobic and steric substituents on the benzene ring have decisive effects on the fungicidal activity against R. solani. The present work describes for the first time the successful bioisosteric replacement of the common SDHI amide moiety by a β-ketonitrile group and highlights the potential of β-ketonitriles as an innovative novel SDHI subclass.

Diphenylsilylsilanolates Enable the Transfer of a Wide Range of Silyl Groups

Development of silylating reagents that can transfer a wide range of silyl groups has been a long-standing challenge. Herein we report sodium diphenylsilylsilanolates as new stable and handy silylating reagents that could be synthesized from chlorosilanes. The new reagents retain the ability of dimethylsilylsilanolates for the delivery of a variety of silyl groups in palladium-catalyzed silylation of aryl bromides irrespective of the steric and electronic properties of silyl groups to be transferred.

Ligand-controlled regiodivergence in cobalt-catalyzed hydrosilylation of isoprene

An atom-economical, regiodivergent hydrosilylation reaction of isoprene was developed using an Earth-abundant cobalt catalyst through variation of ligands.