The Enlightening Development Of New Microbicidal Chemical Entities Inspired From Cryptolepine-Ⅵ

Structural simplification of natural products is an important strategy to make natural products to approved drugs successfully.For now,there are many successful cases of structural simplification,such as Morphine,Pyrethrin I,Strobilurin A and so on.These cases provide us a new way for designing new antimicrobic compounds.Cryptolepine is the alkaloid isolated from the dried roots of the Cryptolepis sanguinolenta,which has various biological activities.In our previous studies,we found that cryptolepine and its derivatives had good activities against plant pathogenic fungi.The EC50 value of Botrytis cinerea was 0.049μg/m L.However,the complicated structure of cryptolepine with poor physicochemical properties limited the application in the antimicrobic field.Therefore,this work simplified the structure of cryptolepine,which would help us find the new compounds with simpler structure,higher biological activities and much better physicochemical properties.The main research contents of this work are:1.Design,synthesis and bioactivity evaluation of new antimicrobic chemical entities based on the simplification of cryptolepine.We designed new antimicrobic chemical entities by simplifying the structure of cryptolepine with opening the C-ring,diversifying the aromatic nucleus and quinoline and modifying the bridge chain contained N.Through the activity screening in vitro,we found that these compounds had good activities against plant pathogenic fungi,especially Botrytis cinerea.Among them,compound A-18 was the most active compound with broad-spectrum antifungal activities.The EC₅₀ value of Botrytis cinerea was 0.259μg/m L and the EC50 values of other tested plant pathogenic fungi were lower than 5μg/m L,such as Sclerotinia sclerotiorum,Rhizoctonia solani,Phytophthora capsica,Fusarium graminearum,Magnaporthe oryzae.Although the antifungal activity against Botrytis cinerea was lower than cryptolepine,compound A-18 displayed higher inhibition than pyrimethanil.2.Design,synthesis and bioactivity evaluation of new antimicrobic chemical entities based on highly active compound A-18.In the above study,we found the highly active compound A-18 with broad-spectrum antifungal activities.Therefore,in this chapter,we designed a series of new compounds which replaced the N in bridge chain with S and O.Through the activity screening in vitro,we found that these compounds also had good activities against plant pathogenic fungi.We found a new compound L-01 in this chapter,which had specific antifungal activities against Botrytis cinerea(EC₅₀=0.156μg/m L).3.Preliminary study on the mechanism of action of highly active compound A-18 on Botrytis cinerea and its bioactivity in vivo.In this chapter,we studied the preliminary mechanism of action of highly active compound A-18 on Botrytis cinerea.We found that compound A-18 could inhibit spore germination and affect the permeability of cell membrane.It could also increase the content of reactive oxygen species in cells.Through the observation of scanning electron microscope（SEM）and transmission electron microscope（TEM）,we found that compound A-18 could affect the growth of mycelium.The cells treated with A-18showed the phenomenon of the plasmolysis and the disappearance of organelles.Meanwhile,a large number of vacuoles appeared in the treated cells.In vivo,compound A-18 had equitant protective effects as cryptolepine but slightly lower curative effects than cryptolepine and had better protective effects than pyrimethanil with equitant curative effects.In summary,we found two highly active compounds,A-18 and L-01.Among them,compound A-18 had more broad-spectrum antifungal activities than cryptolepine in vitro and equitant protective effects as cryptolepine in vivo,which meant that A-18could replace cryptolepine as a fungicide with a simpler synthesis method and structure.Therefore,the structural simplification of cryptolepine in this work was successful,which laid a foundation for further development of new antimicrobic compounds.