Study On The Synthesis,Biological Activity And Structure-Activity Relationship Of URAT1 Inhibitors For The Treatment Of Gout And Hyperuricemia

Gout is the most common inflammatory arthritis caused by the deposition of monosodium urate(MSU)in articular and periarticular tissues and characterized by recurrent joint swelling,redness,warmth and severe pain.Hyperuricemia is the necessary condition of MSU formation and deposition,which is defined as elevated serum uric acid(sUA)levels above the saturation point of MSU in body fluid at physiological pH(7.4)and temperature,i.e.6.8 mg/dL(404 μmol/L).The prevalence and incidence of hyperuricemia and gout have been rising worldwide and the incidence of gout in developed countries is higher than that of developing countries.Uric acid is the final metabolite of dietary and endogenous purine metabolism in humans.Approximately 1/3 of urate is excreted via the gastrointestinal tract,while the remaining 2/3 via kidney.Uric acid is freely filtered at the glomerulus,and more than 90%of the urate filtered in kidney is reabsorbed back into the bloodstream with the remaining less than 10%being excreted in urine;this reabsorption process is mainly mediated by uric acid transporter 1(URAT1).Hyperuricemia is caused by over-production and/or under-excretion of urate,and among the patients with hyperuricemia,greater than 90%of them are urate under-excretors,whereas less than 10%of them are over-producers.Lesinurad is a novel URAT1 inhibitor developed by Ardea Biosciences,and was approved by the FDA in 2005 and by the EMA in 2016 for the treatment of hyperuricemia associated with gout.Lesinurad is the first URAT1 inhibitor approved after the identification of URAT1 in 2002;however,lesinurad suffers from low efficacy and narrow therapeutic window.This thesis is divided into four chapters.The first chapter is the foreword summarizing the recent progression of this field,and the other three chapters are the main research contents.Thus,in the second chapter,in the process of research of URAT1 inhibitors,we have replaced carboxylic acid group in lesinurad structure with its bioisostere tetrazole,leading to the identification of a moderately active URAT1inhibitor Ⅱ-1f which was 2-fold more potent than the parent lesinurad against human URAT1 in vitro.Considering that tetrazole is a promising carboxylic acid bioisostere in many cases and also encouraged by the increased URAT1 inhibitory activity of compound compared with lesinurad,we decided to explore the systematic structure-activity relationship(SAR)focusing on tetrazole moiety.Fortunately,systematic SAR exploration of Ⅱ-1f led to the discovery of a potent URAT1 inhibitorⅡ-1i,which had a novel molecular skeleton and was 11-fold more potent than the parent lesinurad(IC50 = 0.66 μM for II-li vs 7.18 μM for lesinurad).The moderate to strong URAT1 inhibitory activities displayed by the majority of the tetrazole-bearing compounds Ⅱ-1a～Ⅱ-1n suggest that tetrazole was a satisfactory bioisostere of carboxylic acid in present study and warrants further studies.In the third chapter,we focus on the candidate drug Ⅲ-1.The flexible naphthyltriazolylmethane-bearing uric acid transporter 1(URAT1)inhibitor Ⅲ-1 discovered earlier in our laboratories is a novel,highly potent drug candidate for the treatment of hyperuricemia and gout.In order to further understand the effect of substituents at the CH2 linker between the naphthalene and triazole rings on the bioactivity,we designed and synthesized 7 highly congested compounds(Ⅲ-2a～Ⅲ-2g).All the synthesized compounds were characterized by 1H-NMR,13C-NMR and HR-MS and subjected to in vitro URAT1 inhibitory assay.The biological assay results showed that the bioactivity decreased dramatically after the introduction of substituents to the CH2 linker and among the synthesized compounds the bioactivity dropped as the flexibility of the molecules decreased,strongly indicating that any substituents at the CH2 linker were intolerable.The structure-activity relationship(SAR)discovered here will be valuable to the design of URAT1 inhibitors.In the effort to discover potent URAT1 inhibitors based on the structure of lesinurad in our laboratories,earlier studies successfully delivered a number of highly potent URAT1 inhibitors,and the IC50 values of some of them are even lower by almost two orders of magnitude than lesinurad.These highly potent URAT1 inhibitors share a common structural feature,i.e.a carboxylic group connected to a flexible naphthyltriazolylmethane backbone by a linker.Encouraged by the earlier results,we moved forward to expand this specific naphthyltriazolylmethane backbone to a general diarylmethane backbone and carried out a systematic structure-activity relationship(SAR)study on the general backbone as well as the substituents on the a-position of the carboxylic acid group,with an expectation to better understand SAR of this unique flexible structure and discover highly potent URAT1 inhibitors as promising candidate drugs.The SAR study delivered a highly potent URAT1 inhibitorⅣ-1h with a new backbone,i.e.thiophenyltrizolylmethane,which was 200-fold more potent than parent lesinurad(IC50 = 0.035μM against human URAT1 for Ⅳ-1h vs 7.18 μM for lesinurad)and it is the most potent URAT1 inhibitor discovered in our laboratories so far and also comparable to the most potent ones currently under development in clinical trials.The present study strongly suggests that the diarylmethane backbone represents a very promising molecular scaffold for the design of potent URAT1 inhibitors.In conclusion,on the basis of the parent compound lesinurad,we systematically explored SAR of URAT1 inhibitors,and the results obtained are invaluable to the design of URAT1 inhibitors in future.In the course of the study,several potent URAT1 inhibitors have been discovered,and their URAT1 inhibitory activities are comparable to the most effective URAT1 inhibitors currently in clinical trials.