Synthesis Of Novel Naphthalimide Azoles And Their Antimicrobial Study

Naphthalimide compounds are an important type of nitrogen-containing aromatic heterocycles with cyclic double imides and naphthalene framework.This?-sufficient large conjugated planar structure enables naphthalimide derivatives to readily interact with various biological cations,anions,small molecules and macromolecules such as DNAs,enzymes and recetors in living organism via noncovalent bonds,therefore exhibiting extensive potentiality in relatively medicinal applications.Currently,some naphthalimides as anticancer agents have been entered into clinical trials and other naphthalimide-based medicinal developments as potential drugs for treatment of various diseases including bacterial and fungal infections,the diagnosis and detection of life important species etc.,are actively and unprecedentedly expanding.Naphthalimide as a new drug structure with large tricyclic planar system,contains cyclodiimide and naphthalene framework,which enables its derivatives easily to interact with various cations,anions,small molecules,and biomacromolecules(such as DNA,enzymes,and receptors in organisms)via noncovalent bonds,therefore exhibiting extensive potentiality in relatively medicinal applications.Naphthalimide compounds as anticancer drugs have been widely researched,some drug candidate molecules such as amonafide,mitonafide,UNBS5162,elinafide,bisnafide and bibenilone have entered clinical trials,which showing naphthalimide compounds have great potential for clinical application.Other naphthalimide-based medicinal developments as potential candidates for treatment of various diseases are actively and unprecedentedly expanding.The increasing emergence of drug resistance,intractable pathogenic microorganisms and newly arising pathogens have become an increasingly serious and challenging problem for human health all over the world.This situation stimulates an urgent need to develop novel antimicrobial agents with completely different chemical structures possibly exerting different action mechanisms from current clinical drugs.The related research has become a major topic worldwide.There have been a lot of investigations on naphthalimide-based compounds with multi-targeting ability to possess broad spectrum,high activity,low drug resistance development,low toxicity and high bioavailability.All the above mentions strongly point out the great developmental value and spacious potentiality of naphthalimide-based medicinal research and application.Meanwhile,azoles have also been frequently employed in medicinal chemistry and material chemistry resulting from their electron-rich nitrogen heterocycles.This structural characteristic makes their derivatives to easily bind with diverse biological molecules via noncovalent bonds to produce broad bioactivities.So far,lots of azole-based drugs possessing satisfactory pharmacological and biochemical properties have been extensively used in clinic,such as Sulfathiazole,Fluconazole and Ethoxzolamide.On the basis of previous research on antibacterial and antifungal naphthalimides in our group and referring to current situation in the researches on naphthalimides,a series of novel naphthalimide-based compounds were designed and synthesized based on the following ideas,which were expected to produce novel naphthalimide compounds with better biological activity and multi-targeting ability,thus possibly overcoming the severe resistance.These novel compounds were evaluated for their antimicrobial activity,and structure-activity relationships were also discussed and summarized.To identify the safety profile,the cytotoxic tests for the highly active compounds were done against human cells.The further experimental studies including bactericidal kinetic assay,drug resistance development,bacterial membrane permeabilization and theoretical exploration of molecular modeling were also performed to verify the research values and foreground of the naphthalimide-based derivatives.Moreover,the strong active compounds were further investigated for the interaction with DNA in order to explore the possible antibacterial mechanism by the use of U?-visible absorption spectra.Finally,the transportation ability of human serum albumin(HSA)to highly active target compounds was assessed.The main work was summarized as follows:1?Design ideas(1)Design of 1,2,3-Triazole-derived naphthalimides:Some naphthalimide derivatives for the treatment of cancers have been on the clinical trials stage.A lot of work revealed that their anticancer mechanisms were possibly involved in the intercalation into deoxyribonucleic acid(DNA).Recently,some researches have also revealed that naphthalimides exhibited quite large possibility in the treatment of antibacterial and antifungal infections.This encouraged our strong interest in investigating naphthalimide-based compounds as a novel type of potential antimicrobial agents.With the introduction of‘click chemistry',1,2,3-triazole derivatives have opened up a new opportunity to azole antimicrobial agents.The large dipole moment of 1,4-substituted1,2,3-triazoles makes them to be served as hydrogen bond acceptor,which is favor for binding to biological target sites and improving solubility.Moreover,1,2,3-triazole could act as an attractive bridge group to connect two pharmacophores and/or biologically beneficial fragments into one molecule to generate innovative multifunctional compounds.On the basis of this,herein we have overwhelming interest in combinating of 1,2,3-triazole with napthalimide skeleton to develop a novel series of potentially antibacterial hybrids.The new hybrids are expected to exert multi-targeting properties including the validated berberine targeting DNA and membrane activity.(2)Design of naphthalimide aminotriazoles:Naphthalimide is an important N-containing aromatic heterocyclic skeleton with a variety of biological activities.In particular,1,2,4-triazole drugs such as fluconazole,voriconazole and posaconazole are widely used in the antimicrobial field.Therefore,we have introducd 1,2,4-triazole into the naphthalimide skeleton,and different substituents into piperazine to study the effect on biological activity,in the hope of obtaining a new clinical naphthalimide aminotriazoles candidate molecule with high activity and low induction rate of drug resistance.(3)Design of hydrazone-bridged naphthalimide imidazoles:Hydrazone compounds can form metal ion complexes with various metal elements such as transition metals and rare earth metals due to the presence of nitrogen atom.These complexes showed wide range of biological activities.Azoles are one of most important class of nitrogen containing heterocyclic compounds that have been playing crucial roles in medicinal chemistry,in which azole rings could readily accept or donate proton and form various noncovalent interactions,particularly the imidazole-based antimicrobial compounds.Numerous efforts have been devoted to the synthesis of novel imidazole antimicrobial agents,and some excellent drugs like metronidazole and keconazole have been successfully developed and extensively used in clinic.Our previous work revealed that the introduction of azoles into naphthalimide also led to moderate to good antimicrobial effectiveness that was even superior to the references.Herein,we introduced imidazole ring into the 4-position of naphthalimide core via hydrazone bridge to investigate their effect to bioactivities.(4)Design of dimethylamino-naphthalimide azoles:the azoles are a class of important heterocyclic compounds,they could bind readily to enzymes and receptors in living organisms.Dimethylamino fragment could regulate the physicochemical properties and affinity and thus improve the water solubility.The schiff base structure is widely used as a beneficial structural part of antibacterial,antifungal,and anti-inflammatory agents.Therefore,a series of novel dimethylaminonaphthalimide azoles were designed and synthesized.2?Preparation(1)Preparation of novel 1,2,3-Triazole-derived naphthalimides:Commercially available 4-bromo-1,8-naphthalene dimethyl anhydride was treated by hydrazine hydrate to produce intermediate N-amino-naphthalimide ?-4 in 86%yield.The latter was reacted with 3-bromoprop-1-yne in DMF at 70^oC to afford diprop-2-ynylamino-naphthalimide ?-5a and ?-5b in excellent yield.Compounds ?-8,?-9 and ?-10 were easily synthesized in high yields ranging from 75%to 94%by the cycloaddition of compounds ?-5 with alkyl azides ?-6a-c or the substituted benzyl ones ?-7a-j using catalytic amount of copper sulfate and sodium ascorbate in THF/H₂O at room temperature.Compounds ?-9e were treated by hydrogen chloride saturated THF solution at room temperature to produce the corresponding hydrochloride ?-11.Diethanolamino compound ?-12 was obtained by using compound ?-9e and excess diethanolamine at 120 ^oC for 8 h with the yield of 45%.(2)Preparation of novel naphthalimide aminotriazoles:The key intermediates ?-2 was constructed by using commercially available 4-bromo-1,8-naphthalene dimethylenic anhydride and amino-1,2,4-triazole in DMF at 153^oC under nitrogen atmosphere in the presence of zinc acetate.The synthesized intermediate ?-2 was reacted with hydrazine hydrate at 90 ^oC to afford ?-3 in good yields.Compound ?-3were then reacted with chloroacetonitrile,aliphatic bromides or substituted benzyl chlorides to produce the target products ?-4,?-5,?-6 and ?-7.(3)Preparation of novel hydrazone-bridged naphthalimide imidazoles:The commercially available compound ?-1 was treated with 2-ethanolamine in ethanol to afford intermediate ?-2 in 95%yield.Compound ?-2 was further reacted with hydrazine in 2-methoxyethanol at 90^oC to afford intermediate ?-3.Another class of intermediates ?-7a-h and ?-8a-m were obtained by the reaction of benzyl or alkyl halides with raw material ?-6.Finally,intermediate ?-3 was condensated with imidazolecarbaldehyde derivatives ?-7a-h and ?-8a-m in anhydrous ethanol to produce the desirable hydrazone-bridged naphthalimide aryl imidazoles ?-4a-h and alkyl imidazoles ?-5a-m with moderate to good yields ranging from 45.3%to 76.3%.(4)Preparation of dimethylamino-naphthalimide azoles:Commercially available4-bromo-1,8-naphthalene dimethyl anhydride was treated by hydrazine hydrate to produce intermediate N-amino-naphthalimide.The condensation of N-amino-naphthalimide and DMF in the presence of nitrogen using phosphorus pentoxide as dehydrating agent formed the intermediate ?-2 in 96%yields.Compound ?-2 was further reacted with diethanolamine at 120?to yield the intermediate ?-3,?-3 was brominated to get bromide ?-4,and ?-4 was reacted with different azoles to get ?-9.The reaction of N-aminonaphthalimide and diethanolamine produced ?-5,and then was chlorinated by dichlorosulfoxide to afford the target product ?-6.The target products ?-7 and ?-8 were prepared by the reaction of intermediate ?-2 with different nitrogenous heterocycles.3?CharacterizationThe newly synthesized compounds were characterized by ¹H NMR,¹³C NMR,and HRMS spectra.The single crystals of intermediates ?-5a and ?-5b,the target products ?-10g??-7i??-4f and ?-6 were cultured,and X-ray diffraction analysis confirmed their fine geometry.4?Biological activity(1)The antimicrobial assays in vitro indicated that some intermediates and target compounds in the series ?,?,? and V could significantly inhibit the growth of the tested microorganisms including drug-resistant ones.Especially,target3,4-dichlorobenzyl 1,2,3-triazole naphthalimide ?-9e gave strong inhibitory activities against E.coli with low MIC values of 1?g/mL,which were 16-fold and 2 times of the reference drugs chloramphenicol and norfloxacin,respectively.Amino-1,2,4-trizole naphthalimide ?-7j showed significant antibacterial characteristics,especially towards A.fumigosa(MIC=1?g/mL),which was 4 times higher than the reference drugs chloramphenicol and norfloxacin.The naphthalimide compound ?-5h of hydrazylpontine exhibited stronger antibacterial activity than the reference drug norfloxacin,especially against C.tropicals(MIC=1?g/mL),which superior to the current clinical drugs.(2)The bactericidal kinetics and drug resistance test results showed that the above high active compounds showed rapid bactericidal effects and very low drug resistance development.(3)Cytotoxicity test results showed that amino triazolaphthalimide ?-7J and hydrazone ligated naphthalimide ?-5h had little toxicity to normal human cells or cancer cells.(4)Molecular docking showed that aminotriazole naphthalimide ?-7J could have supramolecular interaction with DNA gyrase through hydrogen bonds,thus showing better antimicrobial activity.naphthalimide compound ?-5h could interact with C.tropicals enoyl thioester reductase through hydrogen bonds and hydrophobic supramolecular interactions,the non-covalent interactions helped to stabilize the ?-5h-enzyme complex,thus exhibiting good inhibitory efficacy against the tested strains.(5)It has been found that 1,2,3-triazole naphthalimide ?-9E can be effectively transported by human serum albumin,mainly driven by hydrogen bonding and hydrophobic supramolecular action.Aminotriazole naphthalimide ?-7J can be effectively transported by human serum albumin,mainly driven by hydrogen bonding and hydrophobic supramolecular action.5?Preliminary antibacterial mechanism study(1)The interactive investigation with cell membrane revealed that hydrazone-bridged naphthalimide imidazoles ?-5h were found to be active toward C.tropicals membrane.(2)The supramolecular interactive investigation with DNA revealed that the highly active compounds ?-9e and ?-5h could effectively intercalate/cleave DNA from the sensitive pathogens,to inhibit the DNA replication of bacterial strains,thus exhibiting antimicrobial effects with multi-targeting property.This thesis synthesized 124 compounds with 84 new molecules,including 27 1,2,3-Triazole-derived naphthalimides,21 naphthalimide aminotriazoles,21hydrazone-bridged naphthalimide imidazoles and 15 dimethylamino-naphthalimide azoles.Many prepared compounds exerted better antibacterial effects than reference drugs norfloxacin,chloromycin and/or fluconazole against some strains.The highly active compounds displayed low cytotoxicity to human cells and rapidly bactericidal effects with quite slow resistance development.Also,these active compounds could intercalate and/or cleave DNA,be active toward cell membrane and inhibit the enzyme.All the above indicated that this type of compounds should have great potentiality in the treatment of microbial infections.