Synthesis, fungicidal activity and SAR of 3,4-dichloroisothiazole-based cycloalkylsulfonamides

Abstract To develop more valuable and effective fungicide candidates, a novel series of 3,4-dichloroisothioxazole-based cycloalkylsulfonamides were synthesized and their structures were identified by 1 H NMR, 13 C NMR, MS and elemental analysis. Compound 3k was further confirmed by X-ray single crystal diffraction. The in vitro bioassay results demonstrated that the target compounds showed significant fungicidal activity on mycelial growth and spore germination of Botrytis cinerea . Especially, compound 3j , with prominent inhibition effect on mycelial with EC 50 and EC 80 values of 1.4 and 23.7 μg/mL respectively, was comparable to the selected commercial fungicide. Moreover, at 50 μg/mL, the inhibition rate of compound 3j on spore germination was recorded up to 89.7%. The further in vivo bioassay results indicated compound 3j continued to show high control effect on tomato leaves, flowers and fruit at 200 μg/mL, with control efficiencies of 94.3%, 89.3% and 91.9%, respectively. The structure–activity relationship showed that the compound with a five-membered ring possessed the best activity after the introduction of the active fragment of the 3,4-dichloroisothioxazole, provided a valuable idea for further creation of new fungicides.