Synthesis and Structure-Activity-Relationship Study of 1,4-Acylthizepanes as BD2-Selective BET Bromodomain Inhibitors
Alcoholic hepatitis is characterized by epigenetic dysregulation, involving overexpression of
bromodomain and extra terminal domain (BET) reader proteins binding to N-ε-acetylated lysine residues on histone tails, promoting inflammation. BET proteins (BRD2, BRD3, BRD4, BRDT) contain two tandem bromodomains (BD1 and BD2). Targeting BET proteins regulates gene expression, offering promise as a therapeutic strategy. Current non-selective inhibitors targeting both BDs exhibit dose-limiting toxicities, such as thrombocytopenia and gastrointestinal bleeding. Selective BD2 inhibitors attenuate undesirable side effects in clinical settings, underscoring the need for selective inhibitors. The Pomerantz lab identified a 1,4-acylthiazepane scaffold, demonstrating BD2 inhibition in BET proteins. 1,4-acylthizepanes’ high 3D character allows for conformational diversity, mimicking the acetylated lysine on the histone tail, and allows the ring system to potentially engage a non-conserved histidine residue in BD2. This research focuses on synthesizing 1,4-acylthizepane analogs with diverse benzene ring substituents to optimize the histidine interaction. The synthetic steps involves the formylation of substituted bromobenzenes, dehalogenation, Horner-Wadsworth-Emmons reaction following a hydrolysis to yield carboxylic acids, steglich esterification to produce α,β-unsaturated esters, which then undergo a cyclization with 1,2-aminothiols, yielding 1,4-thiazepanones, followed by reduction and acylation for 1,4-acylthizepanes, confirmed by 1H NMR spectroscopy. Utilizing a competitive ALPHA Screen assay, we assessed the binding affinity and selectivity of 1,4-acylthiazepanes for BRD2-BD2. Preliminary results indicate electron-donating substituents have a 2–3 fold increase in affinity for BRD2-BD2 compared to electron-withdrawing groups, suggesting potential noncovalent interactions of the ring system with the histidine residue of BRD2-BD2. This ongoing work contributes to the development of novel BD2 selective inhibitors for further studies in inflammation models at the Mayo Clinic for targeted therapeutics concerning alcoholic hepatitis treatment.