Study On Construction And Antifungal Activity Evaluation Of Novel Chemical Entities From Benzimidazole

Benzimidazoles have attracted considerable attention in medicinal chemistry due to their diverse biological activities encompassing antibacterial,antiviral,antitumor.Benzimidazoles are,in particular,indispensable precursors in the design and development of highly active antifungal chemical entities.Cryptolepine is a rare alkaloid mainly from Cryptolepis sanguinolenta which is a native medicinal plant in West Africa.Its structural features are indoloquinoline（or quinoline-like structure）skeletons.This alkaloid has many indispensable biological activities including antimalarial,antibacterial,antitumor.Nevertheless,cyptolepine’s applications are restrained by numerous problems such as their scarcity and high toxicity.During our previous studies,we discovered that the antifungal activity of neocryptolepine derivatives against plant pathogens.However,its high toxicity limited its application as plants’antifungal agent.In this study,our research team selected isocryptolepine as the lead compound,which has a skeleton analogous to neocryptolepine.To lay the foundation for subsequent researches,the benzimidazole was used as intermediate,the“Intermediate Derivatization Strategy”was adopted to design and synthesize the“Aza”-type isocryptolepine analogous by introducing different substituents into the Ring A,B and D to explore the effects of different substitutions on the antifungal activity.We also synthesized a series of 2-phenylbenzimidazole thiazole and oxazole derivatives to investigate the antifungal activity based on the structure of the intermediate.To further design and synthesize a series of derivatives of 1-（1H-benzo[d]imidazol-2-yl）-3-phenylprop-2-en-1-one,α,β-unsaturated ketone was introduced into the benzimidazole scaffold for derivatization and antifungal activity evaluation.This research mainly consists of the following three aspects:Part 1.Construction and antifungal activity evaluation of novel“Aza”-type（quinazoline and benzimidazole）chemical entities inspired by the lead model of isocryptolepine.On the basis of our previous research works,the nitrogen atom was inserted into the anthracycline system of the isocryptolepine nucleus to obtain benzo[4,5]imidazo[1,2-c]quinazoline,which named isocryptolepine“Aza”-type structure.The structure was designed and synthesized by introducing different kinds of substituents into Ring A,Ring B（quinoline C-2 position）and Ring D of the compound.And then we evaluated the antifungal activity of the synthesized compounds.Compounds A-0,A-1,A-2 and A-5 demonstrated better antifungal activity than the positive control Azoxystrobin,and compound A-0 exhibited the best inhibition against Botrytis cinerea.The EC₅₀0 value of A-0 was 2.72μg/mL,which is worthy of further research.Part 2.Synthesis and antifungal activity evaluation of benzimidazole intermediates and their derivatives.The“Aza”type compounds of the isocryptolepine were synthesized using 2-phenylbenzimidazole as the intermediate.Motivated by the antifungal activity screening results,the“Common Intermediate Method”was used to guide the design of the target compounds and a series of 2-phenylbenzimidazole,thiazole and oxazole derivatives were synthesized to investigate the effects of substitutions of the small groups on the 2-phenylbenzimidazole/thiazole/oxazole on the antifungal activity.The test results revealed that many compounds like L-2 showed better activity than the control Azoxystrobin.The EC₅₀ value of compound L-2 against Botrytis cinerea was0.19μg/mL,and the EC₅₀0 value of compound L-37 against Sclerotinia sclerotiorum was 0.34μg/mL,respectively.Theα,β-unsaturated ketone structure was introduced into the core structure of the intermediate benzimidazole compound,and optimized to obtain new intermediate compounds.Different heterocyclic systems were constructed according to the“Common Intermediates Method”to investigate the effects of different substituents on the antifungal activity.The antifungal activity of these tested compounds were lower than those 2-phenylbenzimidazole compounds.Nonetheless,the EC₅₀ values of the cyclized compound C were less than 20μg/mL,and the EC₅₀ of the Botrytis cinerea was 6.42μg/mL.Part 3.In vivo tests and antifungal mechanism study of the most active compound L-2Finally,in vivo experiments and antifungal mechanism were performed on the most active compound obtained in the antifungal activity test.The result showed that compound L-2 had an appreciable therapeutic effect on Botrytis cinerea.And it inhibited the growth of Botrytis cinerea by destroying mycelial morphology,devastating the cell membrane integrity,restraining the function of the mitochondria and nucleus at a low concentration（1μg/mL）.