Design, synthesis and biological evaluation of novel evodiamine and rutaecarpine derivatives against phytopathogenic fungi

Evodiamine and rutaecarpine are two alkaloids isolated from traditional Chinese herbal medicine Evodia rutaecarpa, which have been reported to have various biological activities in past decades. To explore the potential applications for evodiamine and rutaecarpine alkaloids and their derivatives, various kinds of evodiamine and rutaecarpine derivatives were designed and synthesized. Their antifungal profile against six phytopathogenic fungi Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum, Fusarium oxysporum, Sclerotinia sclerotiorum, and Magnaporthe oryzae were evaluated for the first time. Furthermore, a series of modified imidazole derivatives of rutaecarpine were synthesized to investigate the structure-activity relationship. The results of antifungal activities in vitro showed that imidazole derivative of rutaecarpine A1 exhibited broad-spectrum inhibitory activities against R. solani, B. cinerea, F. oxysporum, S. sclerotiorum, M. oryzae and F. graminearum with EC50 values of 1.97, 5.97, 12.72, 2.87 and 16.58 μg/mL, respectively. Preliminary mechanistic studies showed that compound A1 might cause mycelial abnormalities of S. sclerotiorum, mitochondrial distortion and swelling, and inhibition of sclerotia formation and germination. Moreover, the curative effects of compound A1 were 94.7%, 81.5%, 80.8%, 65.0% at 400, 200, 100, 50 μg/mL in vivo experiments, which was far more effective than the positive control azoxystrobin. Significantly, no phytotoxicity of compound A1 on oilseed rape leaves was observed obviously even at a high concentration of 400 μg/mL. Therefore, compound A1 is expected to be a novel leading structure for the development of new antifungal agents.