Design, Synthesis and Structure-activity Relationship of Novel Spiro-pyrimidinamines as Fungicides against Pseudoperonospora cubensis.

: Harmful-fugus and the developed resistance to available fungicides seriously threaten the yield and quality of crops, the search for new, highly efficient and resistance-overcoming fungicides remains a quite urgent goal to agricultural scientists. In this study, a series of novel spiro-pyrimidinamine derivatives were designed and synthesized by employing the intermediate derivatization method (IDM). Their structures were identified by 1H NMR, elemental analyses and MS spectra. The structure of compound 5 was further confirmed by X-ray diffraction. Bioassays indicated that a number of the title compounds exhibited some fungicidal activities against Pseudoperonospora cubensis. Especially compound 5 displayed excellent activity (EC50 = 0.42 mg/L), significantly higher than the commercialized fungicides cyazofamid, flumorph and diflumetorim. The structure-activity relationship was also discussed. It was concluded that compound 5 with super fungicidal potency and novel structure is a promising agrochemical fungicide candidate for further development.