Fragment-Guided Discovery of Pyrazole Carboxylic Acid Inhibitors of the Kelch-like ECH-Associated Protein 1: Nuclear Factor Erythroid 2 Related Factor 2 (KEAP1:NRF2) Protein-Protein Interaction

The NRF2-mediated cytoprotective response is central to cellular homoeostasis, and there is increasing interest in developing small-molecule activators of this pathway as therapeutics for diseases involving chronic oxidative stress. The protein KEAP1, which regulates NRF2, is a key point for pharmacological intervention, and we recently described the use of fragment-based drug discovery to develop a tool compound that directly disrupts the protein-protein interaction between NRF2 and KEAP1. We now present the identification of a second, chemically distinct series of KEAP1 inhibitors, which provided an alternative chemotype for lead optimization. Pharmacophoric information from our original fragment screen was used to identify new hit matter through database searching and to evolve this into a new lead with high target affinity and cell-based activity. We highlight how knowledge obtained from fragment-based approaches can be used to focus additional screening campaigns in order to de-risk projects through the rapid identification of novel chemical series.

3,5-Disubstituted-indole-7-carboxamides as IKKβ Inhibitors: Optimization of Oral Activity via the C3 Substituent

IκB kinase β (IKKβ or IKK2) is a key regulator of nuclear factor kappa B (NF-κB) and has received attention as a therapeutic target. Herein we report on the optimization of a series of 3,5-disubstituted-indole-7-carboxamides for oral activity. In doing so, we focused attention on potency, ligand efficiency (LE), and physicochemical properties and have identified compounds 24 and (R)-28 as having robust in vivo activity.

Structure of the BTB domain of Keap1 and its interaction with the triterpenoid antagonist CDDO

The protein Keap1 is central to the regulation of the Nrf2-mediated cytoprotective response, and is increasingly recognized as an important target for therapeutic intervention in a range of diseases involving excessive oxidative stress and inflammation. The BTB domain of Keap1 plays key roles in sensing environmental electrophiles and in mediating interactions with the Cul3/Rbx1 E3 ubiquitin ligase system, and is believed to be the target for several small molecule covalent activators of the Nrf2 pathway. However, despite structural information being available for several BTB domains from related proteins, there have been no reported crystal structures of Keap1 BTB, and this has precluded a detailed understanding of its mechanism of action and interaction with antagonists. We report here the first structure of the BTB domain of Keap1, which is thought to contain the key cysteine residue responsible for interaction with electrophiles, as well as structures of the covalent complex with the antagonist CDDO/bardoxolone, and of the constitutively inactive C151W BTB mutant. In addition to providing the first structural confirmation of antagonist binding to Keap1 BTB, we also present biochemical evidence that adduction of Cys 151 by CDDO is capable of inhibiting the binding of Cul3 to Keap1, and discuss how this class of compound might exert Nrf2 activation through disruption of the BTB-Cul3 interface.

Progress towards the development of anti-inflammatory inhibitors of IKKbeta

The IkappaB kinases (IKKs) are essential components of the signaling pathway by which the NF-kappaB p50/RelA transcription factor is activated in response to pro-inflammatory stimuli such as lipopolysaccharide (LPS) and tumor necrosis factor (TNFalpha). NF-kappaB signaling results in the expression of numerous genes involved in innate and adaptive immune responses. The pathway is also implicated in chronic inflammatory disorders including rheumatoid arthritis (RA), chronic obstructive pulmonary disorder (COPD), and asthma. Inhibition of the kinase activity of the IKKs is therefore a promising mechanism for intervention in these diseases. Here, we will review the literature describing small molecule inhibitors of IKKbeta (IKK2), the most widely studied of the IKKs.

Spongipyran Synthetic Studies. Total Synthesis of (+)-Spongistatin 2

Evolution of a convergent synthetic strategy to access (+)-spongistatin 2 (2), a potent cytotoxic marine macrolide, is described. Highlights of the synthesis include: development of a multicomponent dithiane-mediated linchpin union tactic, devised and implemented specifically for construction of the spongistatin AB and CD spiro ring systems; application of a Ca(II) ion controlled acid promoted equilibration to set the thermodynamically less stable axial-equitorial stereogenicity in the CD spiroketal; use of sulfone addition/Julia methylenation sequences to unite the AB and CD fragments and introduce the C(44)-C(51) side chain; and fragment union and final elaboration to (+)-spongistatin 2 (2) exploiting Wittig olefination to unite the advanced ABCD and EF fragments, followed by regioselective Yamaguchi macrolactonization and global deprotection. Correction of the CD spiro ring stereogenicity was subsequently achieved via acid equilibration in the presence of Ca(II) ion to furnish (+)-spongistatin 2 (2). The synthesis proceeded with a longest linear sequence of 41 steps.

Discovery of 6-aryl-7-alkoxyisoquinoline inhibitors of IkappaB kinase-beta (IKK-beta)

The identification and progression of a potent and selective series of isoquinoline inhibitors of IkappaB kinase-beta (IKK-beta) are described. Hit-generation chemistry based on IKK-beta active-site knowledge yielded a weakly potent but tractable chemotype that was rapidly progressed into a series with robust enzyme and cellular activity and significant selectivity over IKK-alpha.

3-Arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides as novel and selective CXCR2 antagonists

A series of 3-arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides were prepared and shown to be novel and selective antagonists of the CXCR2 receptor. Synthesis, structure and activity relationships, selectivity, and some developability properties are described.

The discovery of 2-amino-3,5-diarylbenzamide inhibitors of IKK-alpha and IKK-beta kinases

A potent and selective series of 2-amino-3,5-diarylbenzamide inhibitors of IKK-alpha and IKK-beta is described. The most potent compounds are 8h, 8r and 8v, with IKK-beta inhibitory potencies of pIC(50) 7.0, 6.8 and 6.8, respectively. The series has excellent selectivity, both within the IKK family over IKK-epsilon, and across a wide variety of kinase assays. The potency of 8h in the IKK-beta enzyme assay translates to significant cellular activity (pIC(50) 5.7-6.1) in assays of functional and mechanistic relevance.