Novel Benzimidazolyl Chalcones And Their Pyrimidine Derivatives: Design, Synthesis And Antimicrobial Study

Chalcones classically consist of two aromatic rings linked by a three-carbon ?,?-unsaturated system,and extensively present in fruits,vegetables,spices,tea,and soy-based food products.Due to great flexibility of ketene skeleton,chalcone compounds could bind with different biomolecules like enzyme or DNA,thus possessing impressive array of biological properties including antibacterial,antifungal,antiinflammatory,antioxidant and anticancer activities.More importantly,the incidence of resistance about chalcones is still very low after the long-term use to treat diseases.The promising biological profile and easy synthetic accessibility of chalcone compounds have attracted increasing interest in new drug design and development.Much literature has revealed that chalcones could be further converted into their cyclic counterparts like flavonoid,oxazole,pyrazole and pyrimidine that are found in many bioactive molecules and clinical drugs.All the above mentions show the enormous potentiality of chalcone-based compounds in medicinal chemistry,which encourage much special interest in exploiting chalcone-based compounds as biological agents.Azole compounds as electron-rich nitrogen heterocycles play an extremely important role in medicinal field.Especially in antimicrobial applications,azole compounds have been extensively investigated as antibacterial and antifungal drugs.Compared with imidazole and triazole,benzene fused azoles like benzimidazoles as well as benzotriazoles possess a larger conjugated system and better electronic transfer property,and are able to readily not only interact with biological active sites such as enzymes and receptors via coordination bonds,hydrogen bonds and so on,but also beneficially modulate the physicochemical and pharmacokinetic properties.Especially,the applications of benzimidazoles and benzotriazoles derivatives in medicinal chemistry have achieved great progress.In this thesis,based on the situation in the researches of chalcone compounds and azoles in recent years,a series of novel azolyl chalcones and their pyrimidine derivatives were designed and synthesized.These novel compounds were evaluated for their antimicrobial activity,and structure-activity relationships were also discussed and summarized.Cytotoxicity of some highly active target compounds were evaluated to predict their pharmacokinetic behaviors.The interaction between highly active target molecules and human serum albumin and the preliminary antibacterial mechanism were also discussed.The main work was summarized as follows:(1)Preparation of new benzotriazolyl chalcones: Intermediates II-2a-c were prepared by the Friedel-Crafts acylation of substituted benzenes II-1a-c respectively with chloroacetyl chloride in dichloromethane,which were further reacted with 1H-benzotriazole under basic conditions to give corresponding N-alkylated benzotriazole derivatives II-3a-c and II-4a-b through nucleophilic substitution.The aldol condensation of intermediates II-3a-c and II-4a-b respectively with equimolar aromatic aldehydes in toluene by the catalysis of piperidine and glacial acetic acid afforded target compounds II-5a-n and II-6a-c.(2)Preparation of benzimidazolyl chalcones and their pyrimidine derivatives: O-phenylene diamine was reacted with 2-hydroxypropanoic acid via cyclization to produce intermediate III-2.The oxidation of hydroxyl group of intermediate III-2 in presence of potassium dichromate provided 2-acetylbenzimidazole III-3.The benzimidazolyl chalcone intermediates III-4a-d were generated from compound III-3 with substituted aromatic aldehyde involving Claisen-Schmidt condensation,which were further subjected to alkylation with a series of alkyl bromides in acetonitrile with potassium carbonate as base to afford intermediates III-5a-p.Intermediates(III-4a-d,III-5a-p)were reacted with the guanidine hydrochloride in the presence of sodium hydride in DMF to prepare the target benzimidazole-pyrimidines III-6a-p and III-7a-d.(3)All the newly synthesized compounds were characterized by 1H NMR,13 C NMR,IR and HRMS spectra.(4)The biological assays indicated that some synthesized ?-benzotriazolyl chalcone compounds showed moderate to good antibacterial activities against the tested strains.Particularly,benzotriazolyl chalcone II-5c was found to be the most potential one against M.luteus with MIC value of 0.5 ?g/mL,being 16-and 2-fold more potent than chloromycin and norfloxacin,respectively.Derivative II–6a displayed superior anti-B.proteus(MIC = 8 ?g/mL)and anti-E.coli(MIC = 8 ?g/mL)activity to chloromycin,and exhibited broad antifungal spectrum and good activities with MICs between 4 and 16 ?g/mL against the growth of tested microorganisms.The antibacterial and antifungal results revealed that some of the benzimidazolyl chalcones could effectively inhibit the growth of the some tested strains including MRSA.Excitingly,some of them were even more active than the reference drugs.It was observed that the conversion of chalcones into aminopyrimidines was helpful to improve the biological activity.Notably,pyrimidine derivative III–7d could effectively inhibit the growth of all the tested bacterial and fungal strains,especially against A.flavus,E.coli DH52 and MRSA with MIC values of 1,1 and 8 ?g/mL,respectively.These indicated that molecule III–7d had the potency to be a lead compound in the development of more effective board-spectrum antimicrobial agents.(5)Drug combination data of compounds II-5e and II-6a with chloromycin,norfloxacin and fluconazole showed better antimicrobial efficiency with less dosage and broader spectrum than their separated use.Notably,MRSA was highly sensitive in drug combination studies.The interaction of highly active compound II–6a with calf thymus DNA revealed that compound II–6a could intercalate into DNA to form II–6a–DNA complex which might be a factor to exert its antimicrobial activity.(6)The active molecule III–7d showed low cell toxicity and did not obviously trigger the development of resistance in bacteria even after 16 passages.Furthermore,compound III–7d was able to beneficially regulate reactive oxygen species(ROS)generation for an excellent safety profile.Molecular docking study revealed that compound III–7d could bind with DNA gyrase by the formation of hydrogen bonds,which correlated with the inhibitory effect.Binding investigations with HSA revealed that HSA could generate fluorescent quenching by III–7d as a result of the formation of ground-state III–7d–HSA complex,and the calculated parameters suggested that association of derivative III–7d with HSA was spontaneous and the hydrophobic interactions and hydrogen bonds played important roles in the transportation of HSA to III–7d.Sixty seven compounds were successfully synthesized in this thesis,in which fifty three compounds were new including twelve intermediates,eight benzotriazole intermediates,six benzimidazole intermediates,seventeen benzotriazolyl chalcone compounds,sixteen alkyl-benzimidazole chalcones,and twenty aminopyrimidine derivatives.