Design, synthesis and fungicidal activity of isothiazole–thiazole derivatives

3,4-Dichloroisothiazoles can induce systemic acquired resistance (SAR) to enhance plant resistance against a subsequent pathogen attack, and oxathiapiprolin exhibits excellent anti-fungal activity against oomycetes targeting at the oxysterol-binding protein. To discover novel chemicals with systemic acquired resistance and fungicidal activity, 21 novel isothiazole-thiazole derivatives were designed, synthesized and characterized according to the active compound derivatization method. Compound 6u, with EC50 values of 0.046 mg L-1 and 0.20 mg L-1 against Pseudoperonospora cubensis (Berk. et Curt.) Rostov and Phytophthora infestans in vivo, might act at the same target as oxysterol binding protein (PcORP1) of oxathiapiprolin; this result was validated by cross-resistance and molecular docking studies. The expression of the systemic acquired resistance gene pr1 was significantly up-regulated after treating with compound 6u for 24 h (43-fold) and 48 h (122-fold). These results can help the development of isothiazole-thiazole-based novel fungicides.