Discovery of novel spiro-piperidine derivatives as highly potent and selective melanin-concentrating hormone 1 receptor antagonists

Optimization of high-throughput screening hit 1a led to the identification of a novel spiro-piperidine class of melanin-concentrating hormone 1 receptor (MCH-1R) antagonists. Compound 3c was identified as a highly potent and selective MCH-1R antagonist, which has an IC₅₀ value of 0.09 nM at hMCH-1R. The synthesis and structure–activity relationships of the novel spiro-piperidine MCH-1R antagonists are described.     

Isoquinoline derivatives as potent CRTH2 antagonists: Design,synthesis and SAR

In this study, we describe the synthesis and structure–activity relationship (SAR) of a series of isoquinoline chemoattractant receptor–homologous molecule expressed on Th2 cells (CRTH2) antagonists. TASP0376377 (15-20), one of the most potent compounds, showed a potent binding affinity (IC₅₀ = 19 nM) in addition to the excellent functional antagonist activity (IC₅₀ = 13 nM). Moreover, the efficacy of this compound in a chemotaxis assay (IC₅₀ = 23 nM) was in good agreement with its potency as a CRTH2 antagonist. In addition, 15-20 exhibited greater selectivity in binding to CRTH2 than to the DP1 prostanoid receptor (IC₅₀ >1 μM) or the enzymes COX-1 and COX-2 (IC₅₀ >10 μM).     

5-(1,3-Benzothiazol-6-yl)-4-(4-methyl-1,3-thiazol-2-yl)-1H-imidazole derivatives as potent and selective transforming growth factor-β type I receptor inhibitors

A series of 5-(1,3-benzothiazol-6-yl)-4-(4-methyl-1,3-thiazol-2-yl)-1H-imidazole derivatives was synthesized as transforming growth factor-β (TGF-β) type I receptor (also known as activin-like kinase 5 or ALK5) inhibitors. These compounds were evaluated for their ALK5 inhibitory activity in an enzyme assay and for their TGF-β-induced Smad2/3 phosphorylation inhibitory activity in a cell-based assay. As a representative compound, 16i was a potent and selective ALK5 inhibitor, exhibiting a good enzyme inhibitory activity (IC₅₀ = 5.5 nM) as well as inhibitory activity against TGF-β-induced Smad2/3 phosphorylation at a cellular level (IC₅₀ = 36 nM). Furthermore, the topical application of 3% 16i lotion significantly inhibited Smad2 phosphorylation in Mouse skin (90% inhibition compared with vehicle-treated animals).     

Aryl sulfonamides containing tetralin allylic amines as potent and selective bradykinin B1 receptor antagonists

The bradykinin B1 receptor has been shown to mediate pain response and is rapidly induced upon injury. Blocking this receptor may provide a promising treatment for inflammation and pain. We previously reported tetralin benzyl amines as potent B1 antagonists. Here we describe the synthesis and SAR of B1 receptor antagonists with homobenzylic amines. The SAR of different linkers led to the discovery of tetralin allylic amines as potent and selective B1 receptor antagonists (hB1 IC₅₀ = 1.3 nM for compound 16). Some of these compounds showed modest oral bioavailability in rats.     

1-(4-Phenylpiperazin-1-yl)-2-(1H-pyrazol-1-yl)ethanones as novel CCR1 antagonists

A novel series of CCR1 antagonists based on the 1-(4-phenylpiperazin-1-yl)-2-(1H-pyrazol-1-yl)ethanone scaffold was identified by screening a compound library utilizing CCR1-expressing human THP-1 cells. SAR studies led to the discovery of the highly potent and selective CCR1 antagonist 14 (CCR1 binding IC₅₀ = 4 nM using [¹²⁵I]-CCL3 as the chemokine ligand). Compound 14 displayed promising pharmacokinetic and toxicological profiles in preclinical species.     

Identification and hit-to-lead exploration of a novel series of histamine H4 receptor inverse agonists

The identification and hit-to-lead exploration of a novel, potent and selective series of histamine H₄ receptor inverse agonists is described. The initial hit, 3A (IC₅₀ 19 nM) was identified by means of a ligand-based virtual screening approach. Subsequent medicinal chemistry exploration yielded 18I which possessed increased potency (R-enantiomer IC₅₀ 1 nM) as well as enhanced microsomal stability.     

Discovery of trisubstituted cyclohexanes as potent CC chemokine receptor 2 (CCR2) antagonists

A series of trisubstituted cyclohexanes was designed, synthesized and evaluated as CC chemokine receptor 2 (CCR2) antagonists. This led to the identification of two distinct substitution patterns about the cyclohexane ring as potent and selective CCR2 antagonists. Compound 36 exhibited excellent binding (CCR2 IC₅₀ = 2.4 nM) and functional antagonism (calcium flux IC₅₀ = 2.0 nM and chemotaxis IC₅₀ = 5.1 nM).     

Development of 6-arylcoumarins as nonsteroidal progesterone antagonists. Structure–activity relationships and fluorescence properties

Progesterone is involved in multiple physiological processes, including female reproduction, via binding to the progesterone receptor (PR). We have developed 6-arylcoumarins such as 5 and 6 as non-steroidal PR antagonists with receptor-binding-dependent fluorescence. In this study, we investigated the structure–activity relationships and fluorescence properties of coumarin derivatives bearing a heterocyclic aromatic moiety. Among these derivatives, 7c (IC₅₀: 34 nM) and 10b (IC₅₀: 24 nM) showed more potent PR-antagonistic activity than lead compounds 5 (IC₅₀: 500 nM) and 6 (IC₅₀: 65 nM) in alkaline phosphatase (AP) assay. Compound 9b showed solvent-dependent fluorescence intensity, exhibiting strong fluorescence in the presence of PR LBD only in buffer solution. On the other hand, 10b showed a solvent-dependent shift of the fluorescence maximum wavelength in the presence of PR LBD. These results indicate that 6-arylcoumarin will be a useful scaffold for PR antagonists and fluorescent probes targeting PR.     

Discovery of 8-azabicyclo[3.2.1]octan-3-yloxy-benzamides as selective antagonists of the kappa opioid receptor. Part 1

Initial high throughput screening efforts identified highly potent and selective kappa opioid receptor antagonist 3 (κ IC₅₀ = 77 nM; μ:κ and δ:κ IC₅₀ ratios >400) which lacked CNS exposure in vivo. Modification of this scaffold resulted in development of a series of 8-azabicyclo[3.2.1]octan-3-yloxy-benzamides showing potent and selectivity κ antagonism as well as good brain exposure. Analog 6c (κ IC₅₀ = 20 nM; μ:κ = 36, δ:κ = 415) was also shown to reverse κ-agonist induced rat diuresis in vivo.     

Synthesis and biological evaluation of thioadatanserin and its dialkylated products as partial 5-HTR1A agonists and 5-HTR2A antagonists for potential use in depression and anxiety disorders

Thionation of adatanserin hydrochloride (2) with Lawesson's reagent in toluene/triethylamine afforded novel compound, (3r,5r,7r)-N-(2-(4-(pyrimidin-2-yl)piperazin-1-yl)ethyl)adamantane-1-carbothioamide (thioadatanserin, 3) in 84–90% isolated yield. Thioadatanserin underwent a tandem double alkylation with methyl iodide and benzyl bromide in NaH/THF to produce novel dialkylated products 6 and 7 respectively. The single X-ray crystal structure of 7 was determined to be 1-(2-((E- ((3r,5r,7r)-adamantan-1-yl)benzylthio)methylene)amino)ethyl)-1-benzyl-4- (pyrimidin-2-yl)piperazin-1-ium bromide showing that the piperazine ring adopts a chair-like configuration that is not co-planar with the pyrimidine ring. Thioadatanserin emerged as a dual potent partial agonist with activity against 5-HTR_1A (EC₅₀ 6.7 nM) and antagonist activity against 5-HTR_2A (IC₅₀ 62.3 nM) and was selective over 5-HTR_2C receptor (IC₅₀ > 3333 nM) in the PathHunter® β-arrestin assays.     

Discovery of substituted 2,4,4-triarylimidazoline derivatives as potent and selective neuropeptide Y Y5 receptor antagonists

Novel imidazoline derivatives were discovered to be potent neuropeptide Y Y5 receptor antagonists. High-throughput screening of Merck sample collections against the human Y5 receptor resulted in the identification of 2,4,4-triphenylimidazoline (1), which had an IC₅₀ of 54 nM. Subsequent optimization led to the identification of several potent derivatives.     

Structure activity relationship studies of 3-arylsulfonyl-pyrido[1,2-a]pyrimidin-4-imines as potent 5-HT6 antagonists

Comprehensive structure activity relationship (SAR) studies were conducted on a focused screening hit, 2-(methylthio)-3-(phenylsulfonyl)-4H-pyrido[1,2-a]pyrimidin-4-imine (1, IC₅₀: 4.0 nM), as 5-HT₆ selective antagonists. Activity was improved some 2–4 fold when small, electron-donating groups were added to the central core as observed in 19, 20 and 26. Molecular docking of key compounds in a homology model of the human 5-HT₆ receptor was used to rationalize our structure–activity relationship (SAR) findings. In pharmacokinetic experiments, compound 1 displayed good brain uptake in rats following intra-peritoneal administration, but limited oral bioavailability.     

Selective antagonists of mouse trace amine-associated receptor 1 (mTAAR1): discovery of EPPTB (RO5212773)

High throughput screening of the Roche compound library identified benzanilides such as 1 and 2 as antagonists of TAAR1. Optimisation of this hit series led to the first selective TAAR1 antagonist (N-(3-Ethoxy-phenyl)-4-pyrrolidin-1-yl-3-trifluoromethyl-benzamide EPPTB (RO5212773, 9f) having IC₅₀ of 28 nM at mouse TAAR1.     

Discovery of a potent and selective small molecule hGPR91 antagonist

GPR91, a 7TM G-Protein-Coupled Receptor, has been recently deorphanized with succinic acid as its endogenous ligand. Current literature indicates that GPR91 plays role in various pathophysiology including renal hypertension, autoimmune disease and retinal angiogenesis. Starting from a small molecule high-throughput screening hit 1 (hGPR91 IC₅₀: 0.8 μM)—originally synthesized in Merck for Bradykinin B₁ Receptor (BK₁R) program, systematic structure-activity relationship study led us to discover potent and selective hGPR91 antagonists e.g. 2c, 4c, and 5g (IC₅₀: 7-35 nM; >1000 fold selective against hGPR99, a closest related GPCR; >100 fold selective in Drug Matrix screening). This initial work also led to identification of two structurally distinct and orally bio-available lead compounds: 5g (%F: 26) and 7e (IC₅₀: 180 nM; >100 fold selective against hGPR99; %F: 87). A rat pharmacodynamic assay was developed to characterize the antagonists in vivo using succinate induced increase in blood pressure. Using two representative antagonists, 2c and 4c, the GPR91 target engagement was subsequently demonstrated using the designed pharmacodynamic assay.     

Discovery of potent transient receptor potential vanilloid 1 antagonists: Design and synthesis of phenoxyacetamide derivatives

We aimed to discover a novel type of transient receptor potential vanilloid 1 (TRPV1) antagonist because such antagonists are possible drug candidates for treating various disorders. We modified the structure of hit compound 7 (human TRPV1 IC₅₀ = 411 nM) and converted its pyrrolidino group to a (hydroxyethyl)methylamino group, which substantially improved inhibitory activity (15d; human TRPV1 IC₅₀ = 33 nM). In addition, 15d ameliorated bladder overactivity in rats in vivo.     

Design,synthesis, and structure–activity relationships of dihydrofuran-2-one and dihydropyrrol-2-one derivatives as novel benzoxazin-3-one-based mineralocorticoid receptor antagonists

Dihydrofuran-2-one and dihydropyrrol-2-one derivatives were identified as novel, potent and selective mineralocorticoid receptor (MR) antagonists by the structure-based drug design approach utilizing the crystal structure of MR/compound complex. Introduction of lipophilic substituents directed toward the unfilled spaces of the MR and identification of a new scaffold, dihydropyrrol-2-one ring, led to potent in vitro activity. Among the synthesized compounds, dihydropyrrol-2-one 11i showed an excellent in vitro activity (MR binding IC₅₀ = 43 nM) and high selectivity over closely related steroid receptors such as the androgen receptor (AR), progesterone receptor (PR) and glucocorticoid receptor (GR) (>200-fold for AR and PR, 100-fold for GR).     

Development of tryptase inhibitors derived from thalidomide

A novel series of tryptase inhibitors with a N-phenylphthalimide skeleton structurally derived from thalidomide (1) has been developed. Structure–activity relationship studies led to a potent and selective tryptase inhibitor, 2-(4-cyanophenyl)isoindole-1,3-dione-5-yl 3-(2-aminopyridin-5-yl)propanoate (7), with the IC₅₀ value of 78 nM.     

Synthesis and SAR of pyrimidine-based, non-nucleotide P2Y14 receptor antagonists

A weak antagonist of the pyrimidinergic receptor P2Y₁₄ containing a dihydropyridopyrimidine core was identified through high-throughput screening. Subsequent optimization led to potent, non-UTP competitive antagonists and represent the first reported non-nucleotide antagonists of this receptor. Compound 18q was identified as a 10 nM P2Y₁₄ antagonist with good oral bioavailability and provided sufficient exposure in mice to be used as a tool for future in vivo studies.     

3-(Arylsulfonyl)-1-(azacyclyl)-1H-indoles are 5-HT6 receptor modulators

Novel 3-(arylsulfonyl)-1-(azacyclyl)-1H-indoles 6 were synthesized as potential 5-HT₆ receptor ligands, based on constraining a basic side chain as either a piperidine or a pyrrolidine. Many of these compounds had good 5-HT₆ binding affinity with K_i values <10 nM. Depending on substitution, both agonists (e.g., 6o: EC₅₀ = 60 nM, E_max = 70%) and antagonists (6y: IC₅₀ = 17 nM, I_max = 86%) were identified in a 5-HT₆ adenylyl cyclase assay.