Discovery Of Triazolopyridazine BRD4 BD1 Selective Inhibitors And Synthesis Of Pyrrolopyridone Compounds

Bromodomain and extraterminal domain（BET）proteins,including BRD2,BRD3,BRD4,and BRDT,have a conserved modular structure,in which two N-terminal tandem BRD-binding domains（BD1 and BD2）recognize acetylated histones and play an important role in promoting gene transcription,thereby regulating the diseases such as inflammation,viral infection and cancer.A number of compounds targeting BET proteins in clinical phases are pan-BET inhibitors（inhibiting both BD1 and BD2）,which exhibited thrombocytopenia,testicular toxicity and gastrointestinal toxicity in clinical progress.Therefore,the development of BD1 and BD2 selective inhibitors will help to understand whether selective inhibitors can reduce the related toxic and side effects.At present,ABBV-744,a selective inhibitor of BD2,is in the phase I of clinical research,and it can reduce the related toxic and side effects.Right now,the selective inhibitor of BET-BD1 is still in the preclinical stage.Its biological functional properties,clinical therapeutic potential,safety and tolerability still need to be further explored.The first part of the work based on the pan-BRD inhibitor bromosporin to discover a series of BET-BD1 selective inhibitors through structure-activity relationship study.BRD4-BD1 inhibitory selectivity over BRD4-BD2 of compound 2-32c is 73.3-fold.This compound also exhibited antiproliferative activity against BRD-sensitive acute myeloid leukemia MV-4-11 cell line with an IC₅₀ value of 0.537μM,comparable to the pan-inhibitor 2-27b.In addition,the co-crystal structure of compound 2-32c with BRD4-BD1 showed that the amide group of compound 2-32c formed a hydrogen bond network with several conserved water molecules and Ile146,and the（R）-methyl group was in hydrophobic loop between Tyr139 and Leu94.The hydrophobic region helps to maintain activity and improve selectivity.This part of the work lays the foundation for further development of compounds with higher BET-BD1 activity and selectivity.PROTACs technology is one of the most noteworthy protein degradation methods proposed in recent years,and it can become a potential new way to treat various diseases.Our previous work determined that 6-azaindole at the 2-position linked with recruited E3 ligase,ligand can produce the BET degrade with a certain selectivity for the degradation of BET protein.In the second part of the work,the key intermediates of the pyrrolepyridone core were synthesized,which can be used to synthesize targeted BET PROTAC degraders,providing a new tool for further exploring the biological functions of BET proteins.