Cytochrome bc1 complex (EC 1.10.2.2, bc1), an essential component of the cellular respiratory chain and the photosynthetic apparatus in photosynthetic bacteria, has been identified as a promising target for new drugs and agricultural fungicides. X-ray diffraction structures of the free bc1 complex and its complexes with various inhibitors revealed that the phenyl group of Phe274 in the binding pocket exhibited significant conformational flexibility upon different inhibitors binding to optimize respective π-π interactions, whereas the side chains of other hydrophobic residues showed conformational stability. Therefore, in the present study, a strategy of optimizing the π-π interaction with conformationally flexible residues was proposed to design and discover new bc1 inhibitors with a higher potency. Eight new compounds were designed and synthesized, among which compound 5c with a Ki value of 570 pM was identified as the most promising drug or fungicide candidate, significantly more potent than the commercially available bc1 inhibitors including azoxystrobin (AZ), kresoxim-methyl (KM), and pyraclostrobin (PY). To our knowledge, this is the first bc1 inhibitor discovered from structure-based design with a potency of subnanomolar Ki value. For all of the compounds synthesized and assayed, the calculated binding free energies correlated reasonably well with the binding free energies derived from the experimental Ki values with a correlation coefficient of r2 = 0.89. The further inhibitory kinetics studies revealed that compound 5c is a non-competitive inhibitor with respect to substrate cytochrome c, but is a competitive inhibitor with respect to substrate ubiquinol. Due to its subnanomolar Ki potency and slow dissociation rate constant (k−0 = 0.00358 s−1), compound 5c could be used as a specific probe for further elucidation of the mechanism of bc1 function and as a new lead compound for future drug discovery.
1-Acetyl-3,-5-diarylpyrazolines have received considerable interests from the fields of medicinal and agricultural chemistry due to their broad spectrum of biological activities. To discover new lead compounds exhibiting both fungicidal and insecticidal activities, a series of pyrazoline derivatives were designed and synthesized by introducing the beta-methoxyacrylate pharmacophore into the scaffold of 1-acetyl-3,5-diarylpyrazoline. The fungicidal activities against Pseudoperoniospora cubensis, Sphaerotheca fuliginea, Botrytis cinerea, and Rhizoctonia solani and the insecticidal activities against Aphis medicagini, Nilaparvata legen, Mythima separata, and Tetranychus cinnabarnus were screened. The most potent compound 13, 1-aceto-3-[m-[o-(E-1-methoxycarboxyl-2-methoxy)-1-yl]benzyloxy]phenyl-5-(benzo-[1,3]-dioxolyl)-4,5-dihydro- pyrazoline, was identified. Its fungicidal IC(50) values against P. cubensis and S. fuliginea are 26.6 and 57.6 microg mL(-1), respectively, while its insecticidal LC(50) value against M. separata is 26.6 microg mL(-1). These results indicated that compound 13 could be used as a lead for further developing new pyrazoline type products exhibiting both fungicidal and insecticidal activities.
Strobilurin derivatives have become one of the most important classes of agricultural fungicide due to a novel action mode, wide fungicidal spectrum, lower toxicity toward mammalian cells, and environmentally benign characteristics. To discover new strobilurin analogues with high activity against resistant pathogens, a series of new chalcone-based strobilurin derivatives are designed and synthesized by integrating a chalcone scaffold with a strobilurin pharmacophore. The preliminary bioassay showed that some of the chalcone analogues exhibited good in vivo fungicidal activities against Pseudoperoniospora cubensis and Sphaerotheca fuliginea at the dosage of 200 microg mL(-1). Two compounds, (E)-methyl 2-[2-({3-[(E)-3-(2-chlorophenyl)acryloyl]phenoxy}methyl)phenyl]-3-methoxyacrylate (1e) and (E)-methyl 2-[2-({3-[(E)-3-(3-bromophenyl)acryloyl]phenoxy}methyl)phenyl]-3-methoxyacrylate (1l), were found to display higher fungicidal activities against P. cubensis (EC90=118.52 microg mL(-1) for 1e and EC90=113.64 microg mL(-1) for 1l) than Kresoxim-methyl (EC90=154.92 microg mL(-1)) and were identified as the most promising candidates for further study. The present work demonstrated that strobilurin analogues containing chalcone as a side chain could be used as a lead structure for further developing novel fungicides. To our knowledge, this is the first report about the syntheses and fungicidal activities of chalcone-based strobilurin derivatives.
Strobilurins are one of the most important classes of agricultural fungicides. To discover new strobilurin analogues with high activity against resistant pathogens, a series of new strobilurin derivatives bearing structurally diverse heterocycle side chains 3a-m and 4a-g were designed and synthesized via a microwave-assisted procedure. The advantages, such as good to excellent yields, shorter reaction times, mild reaction conditions, and simple purification procedures, distinguish the present synthetic protocol as a highly efficient method for the preparation of strobilurin thioether derivatives. Bioassays indicated that most of the compounds showed broad-spectrum fungicidal activity in vitro. Interestingly, as compared to the control of a commercial strobilurin fungicide, Kresoxim-methyl, compounds 3b, 3g, 4c, and 4d possessed remarkably higher in vitro fungicidal activity against six kinds of tested fungi. Exhilaratingly, compound 3g exhibited higher in vivo activity against Sphaerotheca fuliginea and Pseudoperoniospora cubensis than Kresoxim-methyl, and the in vivo fungicidal activities of compound 4d and Kresoxim-methyl against S. fuliginea and P. cubensis are at the same level. The present work demonstrated that strobilurin analogues containing benzothiazole side chains could be used as a lead structure for further developing novel fungicides.
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