Design,Synthesis And Immunosuppressive Activity Evaluation Of Aryalamide As HDHODH Inhibitors And Methodology Development For 3-amino-5-aryl-oxadiazoles

Human dihydroorotate dehydrogenase(hDHODH)is a flavin mononucleotide(FMN)dependent enzyme involved in de novo pyrimidine biosynthesis.It plays a critical role in the rate-limiting step in pyrimidine biosynthetic pathway,which is essential for cellular metabolism and cell growth.Recently,inhibitors of hDHODH have proven efficacy for the treatment of autoimmune disorders.Therefore,developing novel hDHODH inhibitors has attracted considerable attention in this field.In this paper,the structure and function of hDHODH was introduced and the recent development of small-molecule hDHODH inhibitors was summarized.In this thesis,according to the structure-activity relationships of hDHODH inhibitors reported in literatures,taking brequinar and teriflunomide as the leading compounds,both bioisosterism and scaffold-hopping strategies combined with partial modification were applied to design the target compounds.Thus,52 compounds,which belong to two series of arylamide derivatives bearing a 1,2,3-triazole moiety,were designed and synthesized.All the target compounds have not been reported and their structures and relative stereochemistry were confirmed by MS,1H NMR,13C NMR and 2D NOESY NMR spectra.All the target compounds were evaluated for hDHODH inhibitory activities by the DCIP method with teriflunomide as the positive control.The results showed that most compounds displayed moderate to excellent potency against hDHODH.Among them,compounds A4,A15,A18,A19 and A33 exhibited promising potency similar with teriflunomide,with IC50 ranging from 1.5 μM to 2.5 μM.Further modifications led us to obtain compound B8(IC50=0.9 μM),which is more potent than teriflunomide.Based on the enzymatic assays,six compounds were further evaluated for their antiproliferative activities against PBMC cells by CTG assay,using teriflunomide as the positive control.The results showed that similar to teriflunomide,compounds A15 and B8 displayed excellent activties against PBMC with IC50 values of 35.3 μM and 20.4 μM,respectively.compounds A4 and A19 exhibited morderate inhibitory effects.However,compounds A33 and B7 displayed relative low potency.To further elucidate the binding mode,molecular docking of compounds A15,A33 and B8 was performed in the binding site cavity of hDHODH.The co-crystal structure of brequinar with hDHODH was selected as the docking model.It can be observed that all of them adopted a brequinar-like binding mode with matching occupancy of the hydrophobic pocket.The carboxyl group of the amide moiety formed two hydrogen bonds with residues Gln47 and Argl36.However,unlike brequinar,the hydrogen on the amide nitrogen formed additional hydrogen bond with residue Thr360.According to the results of the activities,the SARs were summarized,which is of great significance for the development of novel hDHODH inhibitors.The author also described the construction of 3-amino-5-aryl-1,2,4-oxadiazole derivatives by oxidative cyclization in this paper.1,2,4-Oxadiazole derivatives exist in natural products and are widely applied as drugs in pharmaceuticals.They are important five-membered heterocycles with diverse biological activities.Moreover,they are widely used as bioisosteres of amide or other heterocycles to improve activity and stability.A mild and efficient method for the synthesis of 3-amino-5-aryl-1,2,4-oxadiazole was developed.At room temperature,with the readily available arylformyl guanidine as the substrate,PIDA as the oxidant,N,N-dimethylformamide as the solvent,the target product was obtained by oxidation cyclization.In the optimal conditions,24 3-amino-5-aryl-1,2,4-oxadiazoles were prepared and their structures were confirmed by MS,1H NMR and 13C NMR spectra.The conditions were suitable for a wide range of substrates with different functional groups.A proposed mechanism was illustrated:the process of ionization,deprotonation,and molecular oxidative cyclization were,considered to be involved in the reaction.In view of the mild conditon,high functionality tolerance,and low toxicity,this protocol provides a novel synthetic strategy for 3-amino-5-aryl-1,2,4-oxadiazoles.