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A novel class of experimental fungicides has been discovered, which consists of special tetrasubstituted imidazoles. They are highly active against important phytopathogens, such as Botrytis cinerea (grey mould), Uncinula necator (grape powdery mildew), Mycosphaerella graminicola (wheat leaf blotch) and Alternaria solani (potato and tomato early blight). Their fungicidal efficacy is due to their ability to promote fungal tubulin polymerization, which leads to a disruption of microtubule dynamics. These imidazoles are five-membered ring analogs of similar substituted triazolopyrimidines and pyridazines with the same mode of action. A concise four-step synthesis route has been used to prepare them from commercially available starting materials., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Special tetrasubstituted pyridazines are potent fungicides by promoting the tubulin polymerisation, hereby disrupting the microtubule dynamics in the fungus. They are monocyclic analogs of similar substituted triazolopyrimidines and pyridopyrazines with the same mode of action. The fungicidal activity of these pyridazines was evaluated against the plant pathogens Botrytis cinerea (grey mould), Mycosphaerella graminicola (wheat leaf blotch) and Alternaria solani (potato and tomato early blight). Structure-activity relationship studies revealed the importance of a methyl and a chlorine substituent next to both ring nitrogen atoms and two aryl or heteroaryl groups in the other two pyridazine positions., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: The excellent fungicidal activity of [1,2,4]triazolo[1,5-a]pyrimidines suggested the search for further analogues with improved properties., Results: A series of novel trisubstituted pyrido[2,3-b]pyrazines has been designed and prepared as 6,6-biheterocyclic analogues of related 5,6-bicyclic [1,2,4]triazolo[1,5-a]pyrimidines. Their fungicidal activity was evaluated against the plant pathogens Puccinia recondita Rob. ex Desm. f. sp. tritici (Eriks.) CO Johnston (wheat brown rust), Mycosphaerella graminicola (Fuckel) Schroter (Septoria tritici Rob., leaf spot of wheat) and Magnaporthe grisea (Hebert) Barr (Pyricularia oryzae Cav., rice blast). Structure-activity relationship studies revealed the advantage of a fluoro substituent in position 6 and of a secondary amine in position 8., Conclusion: 8-Amino-7-aryl-6-halogen-substituted pyrido[2,3-b]pyrazines have been prepared as 6,6-biheterocyclic analogues of similarly substituted triazolopyrimidine fungicides. A concise four-step synthesis route has been worked out to prepare these novel compounds from commercially available starting materials. [(R)-(1,2-Dimethylpropyl)]-[6-fluoro-7-(2,4,6-trifluorophenyl)pyrido[2,3-b]pyrazin-8-yl]amine showed excellent activity against three economically important phytopathogens.