Study On Design,Synthesis And Antifungal Activity Of Neocryptolepine Derivatives Against Phytopathogenic Fungi

Cryptolepis sanguinolenta?Lindl.?Schlechter is a traditional medicinal plant native to Africa.Its extract was often used by locals to treat jaundice,hepatitis,gastrointestinal diseases,malaria,diabetes symptoms,hemorrhoids,breast tumor,urinary tract and upper respiratory tract infections,etc.Thus,the pharmacodynamic component of the plant has attracted much attention.Neocryptolepine,one of the effective constituents in this plant,possess an indoloquinoline ring system skeleton in structural characteristics.Previous studies indicated that neocryptolepine have many properties,as antibacterial,antitumor and antimalarial,which makes it a potential lead molecule for new drug development.In the early stage of our research group for screening many alkaloids,it was firstly found that neocryptolepine has a remarkable inhibitory effectiveness on plant pathogens.Based on that,neocryptolepine was treated as a modification and optimization target in this study.Each position of A-ring,B-ring and D-ring was derived,synthesized and optimized to evaluate the structure-activity relationship of neocryptolepine.Furthermore,our research team explored its mechanism of inhibiting phytopathogenic fungi,which provided a theoretical basis and laid a foundation for the further development and application of neocryptolepine.The main research contents are described as follows:Chapter 1:Summarizing and reviewing the research progress of cryptolepis sanguinolenta and neocryptolepine.A detailed review was fisrtly given to describe the plant sources and research advances of cryptolepis sanguinolenta,including the morphological study and the biological activity of the plant and its extracts;Secondly,the research reports of alkaloids were summarized since its isolation and identification,including the research on the activity of neocryptolepine,DiMIQ and C-11 substituted derivatives;Thirdly,the research on total synthesis of neocryptolepine has been summarized.Chapter 2:Research on structural modifications and structure-activity relationships of A and D rings of neocryptolepine.Based on the preliminary result of antifungal screening,substituents of F,Cl,Me,OMe were introduced into the A and D rings of neocryptolepine to discuss the effects of different substituents on the antifungal activity of neocryptolepine in different positions,in addition to explore its detailed structure-activity relationship for further structural optimization research.In the antifungal activity test,the optimal EC₅₀values of compounds 5,21,24,35,40,45,and 47 for the tested phytopathogenic fungi were all less than 1?g/mL,in which the EC₅₀0 value of compound 24 against Botrytis cinerea was 0.07?g/mL.Chapter 3:Research on the design,synthesis and structural optimization of C-11 derivatives of 8-chloro neocryptolepine.Based on the structure-activity relationship in the previous chapter,8-chloro neocryptolepine was used as a lead and applied with the active functional group-oriented strategy to design and synthesize the C-11 substitutes to obtain more candidate compounds with excellent inhibitory for further rational modification research.Chapter 4:Preliminary Study on the Mechanism of Highly Active Compound 24 against Botrytis cinereal.Based on the in vitro antifungal activity of compound 24 against Botrytis cinerea,the inhibition mechanism of compound 24 on Botrytis cinereal was further analyzed.In vivo tests had shown that compound 24 possessed the comparable protective performance with positive control boscalid at concentrations of 50 and 100?g/mL against Botrytis cinereal.In addition,the observation results of scanning electron microscope and transmission electron microscope revealed that Compound 24 caused slight damage to the cell membrane,and affected the normal function of the fungal cell wall and nucleus to a certain extent.Besides,compound 24 completely inhibited the germination of Botrytis cinerea at the concentration of 5?g/mL,and in vitro cytotoxicity experiments indicated that the lethality of compound 24 against HL7702and PC12 cell lines was lower than the positive control azoxystrobin at different concentrations,which are expected to make compound 24 as a lead structure for further development research.