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.

Design, Synthesis, and Antifungal Evaluation of Neocryptolepine Derivatives against Phytopathogenic Fungi.

Neocryptolepine is an alkaloid isolated from traditional African herbal medicine Cryptolepis sanguinolenta, and its broad spectrum of biological activities has been illuminated in past decades. In this study, neocryptolepine and its derivatives (1-49) were designed and synthesized from economical and readily available starting materials. Their structures were confirmed by proton nuclear magnetic resonance, carbon nuclear magnetic resonance, and mass spectrometry. The synthesized compounds were screened for their antifungal profile against six agriculturally important fungi Rhizoctonia solani, Botrytis cinerea (B. cinerea), Fusarium graminearum, Mycosphaerella melonis, Sclerotinia sclerotiorum, and Magnaporthe oryzae. The results of in vitro assay revealed that compounds 5, 21, 24, 35, 40, 45, and 47 presented remarkable antifungal activity against the fungi tested with EC50 values lower than 1 µg/mL. Significantly, compound 24 displayed the most effective inhibitory potency against B. cinerea (EC50 = 0.07 µg/mL), and the data from in vivo experiments revealed that compound 24 demonstrated comparable protective activity with the positive control boscalid. Preliminary mechanism studies indicated that compound 24 showed impressive spore germination inhibitory effectiveness and lower cytotoxicity than azoxystrobin, imparted on normal function of the cell membrane and cell wall, and arrested the normal function of the nucleus. Besides the excellent inhibitory activity against agriculturally important phytopathogenic fungi tested, the designed assemblage possesses several benefits with a high profile of variation in synthesized molecules, the ease of synthesis, and good cost-effectiveness of commercially available synthetic reagents, all of these have highlighted the potential worth of compound 24 as a new and highly efficient agricultural fungicide.

Acaricidal activity and enzyme inhibitory activity of active compounds of essential oils against Psoroptes cuniculi.

Plant essential oils and its chemical compositions are commonly applied in medicinal and other industries due to their broad advanced pharmacological activities. In the present study, we systematically evaluated the acaricidal activities of twelve compounds of essential oils against Psoroptes cuniculi in vitro and in vivo. In addition, to support the clinic uses, their toxicities against immortalized human keratinocytes (HaCaT) and human liver cells (HL-7702) and skin irritation were studied for evaluating the liver and skin safety. The possible mechanism of action of certain chemical were investigated by determining the inhibitory activities against cytochrome P450 (P450) acetylcholinesterase (AChE) and glutathione-S-transferase (GST). Among all tested compounds, eugenol exhibited the best acaricidal activity with LC50 value of 56.61 µg/ml in vitro. Meanwhile, after the treatment of eugenol for five times within 10 days, the P. cuniculi were eliminated in the naturally infested rabbits, no skin irritation was found in rabbits treated by eugenol. Moreover, eugenol presented no or weak cytotoxicity against HaCaT cells and HL-7702 cells with IC50 values of greater than 100 µg/ml. Furthermore, the moderate inhibitory activities of eugenol against mites P450 and AChE were demonstrated. Above results indicated that eugenol presented the promising acaricidal activity against P. cuniculi in vitro and in vivo, is safe for both humans and animals at the given doses. This work lays the foundation for the development of eugenol as an environmentally friendly acaricide agent.