Synthesis, Fungicidal Activity Of 3,4-dichloroisothiazolamides

In order to find new and efficient fungicides,three series of 81 novel 3,4-dichloroisothiazole derivatives were designed and synthesized by using 3,4-dichloroisothiazole ring as the parent,introducing diamides,1,2,4-oxadiazole and cycloalkyl sulfonamides and their structures were identified by ¹H NMR,¹³ C NMR,MS and elemental analysis.Fungicidal activity was evaluated by common methods.In vitro bioassay results showed that all compounds showed different inhibitory effects on Botrytis cinerea,Pyricularia grisea,Fusarium graminearum and Pythium aphanidermatum.At 50 ?g/m L,compounds I-7,III-9,III-10,III-11,III-13 exhibited significant inhibitory effects on B.cinerea and P.grisea,with EC50 values of 1.6,3.8,1.4,1.6,2.7 ?g/m L for B.cinerea,and 1.3,3.1,1.6,3.2,2.4 ?g/m L for P.grisea,respectively,which were comparable to the corresponding control agents.However,the EC80 values of compounds I-7 and III-10 were similar to those of control agents when compared with EC80 values.In addition,at 50 ?g/m L,compounds III-9,III-10 and III-11 also showed inhibitory effects on spore germination of B.cinerea,with inhibition rates of 82.2,89.7 and 83.5%,respectively.In vivo bioassay results showed that some compounds had high control effects on B.cinerea,Pseudoperonospora cubensis and Colletotrichum orbiculare.Compounds I-7,III-9 and III-10 were more than 80% effective against B.cinerea on tomato leaves,flowers and fruits at 200 ?g/m L,of which compound III-10 was the most prominent,with control effeciencies of 94.3,89.3,91.9%.In addition,at 100 ?g/m L,compound I-7 expressed prominent control effect against P.cubensis,with control effeciency of 90% and the control effeciency of 13 compounds against C.orbiculare exceeded 80%,of which compounds I-11,II-17,II-18 and II-20 were more than 90%.Structure-activity relationship analysis: 1)When small halogenated alkyl groups such as trifluoromethyl and trichloromethyl were introduced into the structure of diamides,compounds showed higher fungicidal activity against B.cinerea and P.grisea,and outstanding control effect against C.orbiculare.2)The introduction of the 1,2,4-oxadiazole heterocycle increaseed the control effect of compounds on cucumber anthracnose,when the 5-position of the 1,2,4-oxadiazole heterocycle was substituted with heterocyclic ring,the compound exhibits higher fungicidal activity.3)In the structure of cycloalkylsulfonamides,compound with a five-membered ring possessed the best activity after the introduction of the active fragment of the 3,4-dichloroisothioxazole,and the fluorine atom had a significant influence on the fungicidal activity.In this paper,the research scope of 3,4-dichloroisothiazolamides was broadened in terms of fungicidal activity,and new structure-activity relationship was explored,which provided theoretical basis for further research on compound design,fungicidal activity screening and mode of action.