Design, synthesis and antifungal activity of new substituted difluoromethylpyrimidinamine derivatives

Rusts are one of the most important fungal diseases, the known target sites have already developed serious resistance to the main existing classifications of fungicides. In order to discover novel fungicides with a promising activity on rusts, twenty new substituted difluoromethylpyrimidinamine derivatives were designed and synthesized with the aid of the intermediate derivatization methods starting from ethyl 4,4-difluoro-3-oxobutanoate that is the common raw material in some newly launched important succinate dehydrogenase inhibitor (SDHI) fungicides. Their structures were identified by H-1 NMR, C-13 NMR, F-19 NMR, IR, elemental analyses and HRMS. All the compounds were screened for in vivo fungicidal activity against southern corn rust (SCR). The preliminary bioassay results indicated that 5-chloro-6-(difluoromethyl)-N-(2-(6-(3-(trifluoromethyl) phenoxy)pyridin-3-yl)ethyl)pyrimidin-4-amine (compound..); R-1 = CHF2, Alk.= CH2CH2, Rn = 3-CF3) is the optimal structure with desired fungicidal activity against SCR (EC50 = 2.16 mg/L), significantly higher than commercial fungicides diflumetorim (EC50 = 53.26 mg/L) and propiconazole (ECso = 3.92 mg/L). The structure activity relationship of the synthesized compounds was discussed as well. This study also demonstrated that difluoromethylpyrimidinamine derivatives can be further utilized as a promising antifungal agent to control rust. Further synthesis and structure optimization studies are currently in progress.