Design,Synthesis And Biological Evaluation Ofindole Carboxamide Derivatives And Analogs

Investigations during the last few decades have established the essential role in cancer treatment of epidermal growth factor receptor(EGFR),which belongs to the human epidermal growth factor receptor(HER)family of receptor tyrosine kinases.As known,EGFR family comprises four distinct members,including EGFR(HER1/ErbBl),HER2(ErbB2/neu),HER3(ErbB3)and HER4(ErbB4).Because of its significant function in cells life and widely distribution in the cells,EGFR has already become one of the most promising targets of antitumor drug research.In addition,EGFR has proved to be related to the development,progression,aggressiveness,and metastasis of many solid tumors.Therefore,the inhibition of EGFR turns into a beneficial antitumor therapeutic strategy.Previous studies have showed that a series of 4-anilinopyrimidoindole derivatives especially representative compound N-(3-bromophenyl)-6-methoxy-9H-pyrimido[4,5-b]indol-4-amine exhibited antiproliferative activity as potent inhibitors of EGFR.Based on these tricyclic systems,the structure of lead compound was simplified and the pyrimidine ring was opened to get indole-3-carboxamide derivatives as the target compounds.Meanwhile,according to principleof scaffold hopping,bioisosteresand combination,based on N-(2,6-dichlorophenyl)-6-methylbenzothiazol-2-amine has exhibited remarkable antitumor activity asan EGFR inhibitor,a series of benzothiazole-2-carboxamide derivativesas analogs of indole-3-carboxamide derivatives were designed.Moreover,molecular docking studies were presented as well.According to the literatures and retrosynthetic analysis,a novel series of indole-3-carboxamide derivatives were synthesized starting from ethyl acetoacetate.Reaction of ethyl acetoacetate with methylamine or ethylamine afforded ethyl(Z)-3-(substituted amino)but-2-enoate,which was converted to ethyl 1-alkyl-5-hydroxy-2-methyl-1H-indole-3-carboxylate via Nenitzescu reaction with 1,4-benzoquinone.Hydrolysis of 1-alkyl-5-hydroxy-2-methyl-1H-indole-3-carboxylate gave 1-alkyl-5-hydroxy-2-methyl-1H-indole-3-carboxylic acid.Treatment of the acid with substituted amines in the presence of EDCI and HOBt and then the products reacted with corresponding 2-chloroacetamide derivatives by using anhydrous K2CO3 and KI to give 1-alkyl-2-methyl-5-(2-substitutedamino-2-oxoethoxy)-1H-indole-3-carboxamide.Similarly,with the aim of preparing a series of novel benzothiazole-2-carboxamide derivatives,the initial steps of the synthesis of target compounds from L-cysteine were carried out.Reaction of L-cysteine with ethanol and SOCl2 afforded L-cysteine ethyl ester hydrochloride,which was converted to ethyl 6-hydroxybenzothiazole-2-carboxylate with 1,4-benzoquinone followed by an oxidation-cyclization step.Reaction of this intermediate with corresponding 2-chloroacetamide by using anhydrous K2CO3 and KI and then the products reacted with substituted amines via ammonolysis to obtain benzothiazole-2-carboxamide derivatives as the target compounds.The structures of all target compounds were characterized by IR,ESI-MS and NMR and the compounds were not reported in literatures in accordance with the search results by SciFinder.All of the target compounds were evaluated for the anticancer activitiesin vitro against EGFR high-expressed cancer cell lines(A549,HeLa and SW480),EGFR low-expressed cell line(HepG2)and human liver normal cell line(HL7702)using MTT assay.Several target compounds showed moderate to excellent potency against A549,HeLa,SW480 and weak cytotoxic effects on HepG2,showing they are probably EGFR inhibitors.And they also exhibited scarcely any activities against HL7702,which implies they are likely to overcome the nonspecific toxicity against normal cells.The target compounds N-(4-fluorobenzyl)-5-{2-{[2-(2-methoxyphenoxy)ethyl]amino}-2-oxoethoxy}-1,2-dimethyl-1 H-indole-3-carboxamide(ZhL-23),1-ethyl-N-(4-fluorobenzyl)-5-{2-{[2-(2-methoxyphenoxy)ethyl]amino}-2-oxoethoxy}-2-methyl-lH-indole-3-carboxamide(ZhL-24),1-ethyl-N-(furan-2-ylmethyl)-5-{2-{[2-(2-methoxyphenoxy)ethyl]amino}-2-oxoethoxy}-2-methyl-1H-indole3-carboxamide(ZhL-60),5-[2-(benzylamino)-2-oxoethoxy]-N-(3,4-dimethoxyphenethyl)-1-ethyl-2-methyl-1H-indole-3-carboxamide(ZhL-68),6-[2-(diethylamino)-2-oxoethoxy]-N[2-(2-methoxyphenoxy)ethyl]benzothiazole-2-carboxamide(ZhL-79),6-[2-(diethylamino)-2oxoethoxy]-N-(furan-2-ylmethyl)benzothiazole-2-carboxamide(ZhL-88)and 6-[2-(diethyl amino)-2-oxoethoxy]-N-(3,4-dimethoxyphenethyl)benzothiazole-2-carboxamide(ZhL-94)demonstrated excellent strong anticancer activities.What’s more,a new EGFR inhibitor scaffold and a preliminary discussion on their SARs provide promising opportunities to guide further research on indole-3-carboxamide derivatives and their analogs as novel EGFR-TKIs.