Design,Synthesis And Agricultural Bioactivity Of Walsuchin Nortriterpenoids And Their Intermediate Derivatives

The creation of novel green pesticides majorly comes from structural optimizations of natural products.Nortriterpenes are a class of compounds showing structural diversity and demonstrating wide ranging biological activities,including anticancer,anti-HIV,antifeedant and anti-inflammatory activities.Walsucochin nortriterpenes have received extensive attentions from chemists due to their novel chemical structures and elevated biological activities.However,their natural abundance is extremely low,so chemical synthesis is the most efficient way to obtain them so far.Based on the previous work from our research group,the key intermediate 38 was used as the starting material to complete the total syntheses of walsuchin A,walsuchinoids C-F and their analogues,meanwhile the agricultural activity studies on the target compounds and intermediate derivatives were investigated.The specific contents are as follows:In the first section,the natural products bearing important biological activities of walsuchin nortriterpenoids were synthesized and characterized.The intermediate 38 was used as the starting material:firstly,hydroxyl inversion through oxidation and reduction reactions was conducted;subsequently,the conjugated carbonyl group was constructed through the one pot oxidative dehydrogenation reaction;finally,the total syntheses of walsuchin A,walsuchinoids C-F,and their analogues were accomplished via a metal catalyzed coupling reaction as the key step.The chemical structures were characterized by ¹H NMR,¹³C NMR and HRMS respectively.This study provides a highly efficient and concise synthetic strategy（6-8 steps）from intermidate 38 for the preparation of walsuchin nortriterpenoids and analogues,expanding the chemical space of this class of compounds and providing important references for the subsequent syntheses of related natural products.Meanwhile the characterizations on biological activities indicated that compounds 6,57 and 60 have good inactivation activities against tobacco mosaic virus,with EC₅₀ of 244.1μg/m L,314.6μg/m L,and 279.1μg/m L,respectively.In the second section,23 terpene derivatives were synthesized from the key intermediate62,obtained by the research group from previous work,by esterification with various substituted benzoic acids and benzoyl chlorides.The fungicidal activities of these 24compounds against several agricultural plant pathogens,for example Botrytis cinerea,Valsa mali,Sclerotinia sclerotiorum,Gaeumannomyces graminis,Rhizoctonia solani and Phytophthora capsici were determined by the mycelial growth rate method.The experimental results revealed that derivates 63,64,72 and 73 demonstrate promising in vitro antifungal activities against Sclerotinia sclerotiorum,with EC₅₀ values of 12.20μg/m L,10.36μg/m L,9.78μg/m L and 9.39μg/m L,respectively.In summary,this work provides a lead compound for the further development of green antiviral agents for plants;It also provides a good theoretical guidance for the agricultural antifungal activity applications of 6/6/5-ring-containing terpenoids.