Synthesis Of Chloroxaloterpin A And B Produced By Actinomycetes, Their Antifungal Activity Against Botrytis Cinerea

Botrytis cinerea is an airborne pathogen that infects nearly 1400 host plants worldwide and can cause huge economic losses.In recent years,the problem of B.cinerea resistance has become increasingly prominent.It is urgent to develop new and effective fungicides to control gray mold.Previous studies show that 1 and 2 have a good inhibitory effect on spores germination of B.cinerea,with EC₅₀values of 4.40 and 4.96 mg/L,respectively.However,due to the low yields of 1 and 2,other aspects of bioactivity have not been studied.Viguiepinol（3）is the main secondary metabolite of Streptomyces SN194,and has the same skeleton with 1 and 2,but its biological activity against B.cinerea is poor.In this study,chloroxaloterpin A（1）and B（2）are synthesized using viguiepinol（3）as the diterpenoid precursor compound,and their biological activities against B.cinerea are further studied.Relevant research results are as follows:Acyl chloride（6）containing chloroxaloterpin A side chain is synthesized from o-chloroaniline（4）by two-step acylation reaction.Through the esterification reaction of 6 and3,the side chain structure is connected to the skeleton of viguiepinol to obtain compound 1with a yield of 90%;Acyl chloride（9）containing chloroxaloterpin B side chain structure is synthesized from o-chloroaniline（4）by condensation,hydrolysis,acidification and chlorination.Through the condensation reaction of 9 and 3,the side chain structure is connected to the skeleton of viguiepinol to obtain 2 with a yield of 33%.The effects of 1 and 2（100 mg/L）on the surface morphology and internal structure of B.cinerea spores are observed by scanning electron microscope（SEM）and transmission electron microscope（TEM）observations,respectively.The results show that the surface of the spores collapse and deform,the plasma membranes are blurred,and the cytoplasm leak.1and 2 are further confirmed to damage the cytoplasmic membrane of B.cinerea spores by PI staining and fluorescence microscopy observation.By inoculating B.cinerea onto tomato fruit,the in vivo antibacterial effect of 1 and 2against B.cinerea is detected.The results show that 1 and 2（100 mg/L）can not inhibit mycelial growth of B.cinerea,but can effectively inhibit the sporulation of B.cinerea.In curative efficacy,sporulation inhibitory rates of 1 and 2 reach 98.8%.In protective efficacy,sporulation inhibitory rates of 1 and 2 are 99.0%and 95.0%,respectively.The above results indicate that chloroxaloterpin A（1）and B（2）have good development potential,which lay a good research foundation for the development of new pesticide lead compounds.