Design And Synthesis Of Substituted Indole Compounds And Evaluation Of Their Anti-respiratory Syncytial Virus And Anti-influenza Virus Activities

Virus infection is the main pathogen of acute respiratory infections including pneumonia.Respiratory syncytial virus and influenza viruses are two of most frequently detected virus in the patients.RSV is a negative stranded nonsegmented RNA virus of pneumovirus family.It is the leading cause of hospitalization for infants,especially those born premature or with chronic lung or heart disease.Furthermore,Currently,the treatment therapy is limited to the non-specificity antiviral drug ribavirin,which is teratogenic and has limited efficacy.The monoclonal antibody palivizumab has demonstrated effectiveness as prophylaxis in infants who are premature or have underlying comorbidities.Influenza A viruses(IAV)is a negative stranded segmented RNA virus.IAV,rather than Influenza B viruses(IBV)is responsible for most cases of epidemic influenza.IAV is often associated with more-severe symptoms,morbidity,and mortality due to a greater genetic diversity typified by chromosomal.Currently,there are only two main classes of antiviral drugs used against influenza:M2 ion channel inhibitors,also called adamantanes(amantadine and rimantadine);and neuraminidase inhibitors(oseltamivir and zanamivir),available for combating influenza A spread.However,most of influenza A strains became resistant to adamantanes,and strains resistant to oseltamivir and zanamivir also was reported.Patients infected with either influenza virus or RSV can present with similar early symptoms,however,the course of therapy and choice of antiviral agent are different for both viruses.The lack of a reliable and fast bedside test to rapidly confirm the viral etiology makes it is impossible to give an early administration of antiviral agent which is an important step toward reducing the use of drugs,especially in hospitalized children.Alternatively,discovering of new chemical entities active against both RSV and IAV is a simple and an efficient strategy for the quick treatment of respiratory infections.In this work,we have initially identified 29 compounds as potent RSV inhibitors using an rRSV-mGFP high-throughput screening assay.After considering the toxicity,druggability and synthesis feasibility of these compounds,compounds 1(2-((1H-indol-3-yl)thio)-N-(2-ethoxyphenyl)acetamide)and 2(2-((1H-indol-3-yl)thio)-N-(3,4-dichloro-phenyl)acetamide)were selected as two candidates for further optimization.These compounds show high inhibition(77.14%and 83.24%for 1 and 2,respectively)in a fluorescence-based assay with no toxicity to HEp-2 cells at 50μM.As these two candidates share a common scaffold of 2-((1H-indol-3-yl)thio)acetamide,we suppose this fragment is crucial for the RSV inhibition and we intend to introduce varies substituent groups at different position of this core structure to increase their anti-virus potency.The aniline in area C was substituted with methyl,tert-butyl,benzyl,trifluoromethyl,methoxy,ethoxy,and different halogens,and it is also replaced with different benzylamines.Then thioethers were also being oxidized to sulfoxide and sulphone to afford 2 additional series of derivatives.Finally,a methyl group,a methoxyl or a chlorine atom was introduced to the indole,and an additional series of derivatives was designed and synthesized.All of these compounds were evaluated for their anti-RSV and anti-IAV activity.In this paper,we designed and synthesized three series of target compounds,including 2-(substituted 1H-indol-3-yl)thio-N-phenylacetamide(A-zone modification),N-substituted-((1 H-indol-3-yl)sulfinyl/sulfonamido)acetamide(B-zone modification)and N-substituted phenyl-2-((1H-indol-3-yl)thio)acetamide(C-zone modification),according to the structural characteristics of lead compounds 1 and 2.The target products were evaluated for their anti-RSV and anti-IAV activity and thus the effects of structural modification of different regions on their anti-virus activity was revealed.And the mechanism of action of the compounds was also studied.A total of 110 target compounds were synthesized in this paper.The structures of all target products were confirmed by HPLC-MS,1H NMR,13C NMR and HR-MS.Most of the compounds showed excellent to moderate activity against both RSV and IAV viruses in a dose-dependent manner;the EC50 values of compounds 10o,10p,10r,10u,10w,10y for RSV were 4.46 ± 0.28,5.58 ± 0.02,2.45 ± 0.40,9.95 ± 0.28,0.43±0.10 and 4.82 ± 0.99 μM,respectively,whose activity is significantly better than ribavirin(EC50 is 15.83 ± 3.38μM).Compound 10g,10h,10o,10p,10r,10y and 10ae are the most active IAV inhibitors with EC50 values of 3.50±0.48,0.64±0.02,1.75±0.96,1.53±0.39,0.58±0.22,1.27±0.07 and 1.90±0.05 μM,respectively,and show a higher safety index(more than 10 times higher)than control drugs ribavirin.The most effective and lest-toxic compounds 10o and 10y have the potential to be further developed as dual inhibitors of RSV/IAV.A preliminary mechanism of action was carried out on some of the preferred compounds,and the results showed that these compounds exert antiviral effects by acting on the replication stage after the virus enter the cell.