A knowledge-based, structural-aided discovery of a novel class of 2-phenylimidazo[1,2-a]pyridine-6-carboxamide H-PGDS inhibitors.

Through an internal virtual screen at GlaxoSmithKline a distinct class of 2-phenylimidazo[1,2-a]pyridine-6-carboxamide H-PGDS inhibitors were discovered. Careful evaluation of crystal structures and SAR led to a novel, potent, and orally active imidazopyridine inhibitor of H-PGDS, 20b. Herein, describes the identification of 2 classes of inhibitors, their syntheses, and their challenges.

The exploration of aza-quinolines as hematopoietic prostaglandin D synthase (H-PGDS) inhibitors with low brain exposure.

GlaxoSmithKline and Astex Pharmaceuticals recently disclosed the discovery of the potent H-PGDS inhibitor GSK2894631A 1a (IC50 = 9.9 nM) as part of a fragment-based drug discovery collaboration with Astex Pharmaceuticals. This molecule exhibited good murine pharmacokinetics, allowing it to be utilized to explore H-PGDS pharmacology in vivo. Yet, with prolonged dosing at higher concentrations, 1a induced CNS toxicity. Looking to attenuate brain penetration in this series, aza-quinolines, were prepared with the intent of increasing polar surface area. Nitrogen substitutions at the 6- and 8-positions of the quinoline were discovered to be tolerated by the enzyme. Subsequent structure activity studies in these aza-quinoline scaffolds led to the identification of 1,8-naphthyridine 1y (IC50 = 9.4 nM) as a potent peripherally restricted H-PGDS inhibitor. Compound 1y is efficacious in four in vivo inflammatory models and exhibits no CNS toxicity.

The discovery of quinoline-3-carboxamides as hematopoietic prostaglandin D synthase (H-PGDS) inhibitors.

With the goal of discovering more selective anti-inflammatory drugs, than COX inhibitors, to attenuate prostaglandin signaling, a fragment-based screen of hematopoietic prostaglandin D synthase was performed. The 76 crystallographic hits were sorted into similar groups, with the 3-cyano-quinoline 1a (FP IC50 = 220,000 nM, LE = 0.43) being a potent member of the 6,6-fused heterocyclic cluster. Employing SAR insights gained from structural comparisons of other H-PGDS fragment binding mode clusters, the initial hit 1a was converted into the 70-fold more potent quinoline 1d (IC50 = 3,100 nM, LE = 0.49). A systematic substitution of the amine moiety of 1d, utilizing structural information and array chemistry, with modifications to improve inhibitor stability, resulted in the identification of the 300-fold more active H-PGDS inhibitor tool compound 1bv (IC50 = 9.9 nM, LE = 0.42). This selective inhibitor exhibited good murine pharmacokinetics, dose-dependently attenuated PGD2 production in a mast cell degranulation assay and should be suitable to further explore H-PGDS biology.

2,4-Diamino-8-quinazoline carboxamides as novel, potent inhibitors of the NAD hydrolyzing enzyme CD38: Exploration of the 2-position structure-activity relationships.

Starting from 4-amino-8-quinoline carboxamide lead 1a and scaffold hopping to the chemically more tractable quinazoline, a systematic exploration of the 2-substituents of the quinazoline ring, utilizing structure activity relationships and conformational constraint, resulted in the identification of 39 novel CD38 inhibitors. Eight of these analogs were 10-100-fold more potent human CD38 inhibitors, including the single digit nanomolar inhibitor 1am. Several of these molecules also exhibited improved therapeutic indices relative to hERG activity. A representative analog 1r exhibited suitable pharmacokinetic parameters for in vivo animal studies, including moderate clearance and good oral bioavailability. These inhibitor compounds will aid in the exploration of the enzymatic functions of CD38, as well as furthering the study of the therapeutic implications of NAD enhancement in metabolic disease models.

Novel heterocyclic scaffolds of GW4064 as farnesoid X receptor agonists.

The farnesoid X receptor (FXR) may play a crucial role in a number of metabolic diseases and, as such, could potentially serve as a target for the development of therapeutics as a treatment for those diseases. Previous work has described GW4064 as an FXR agonist with an interesting activity profile. This manuscript will describe the synthesis of novel analogs of GW4064 and the activity profile of those analogs.

Conformationally constrained farnesoid X receptor (FXR) agonists: alternative replacements of the stilbene.

To further explore the optimum placement of the acid moiety in conformationally constrained analogs of GW 4064 1a, a series of stilbene replacements were prepared. The benzothiophene 1f and the indole 1g display the optimal orientation of the carboxylate for enhanced FXR agonist potency.

Conformationally constrained farnesoid X receptor (FXR) agonists: heteroaryl replacements of the naphthalene.

To improve on the drug properties of GSK8062 1b, a series of heteroaryl bicyclic naphthalene replacements were prepared. The quinoline 1c was an equipotent FXR agonist with improved drug developability parameters relative to 1b. In addition, analog 1c lowered body weight gain and serum glucose in a DIO mouse model of diabetes.

Substituted isoxazole analogs of farnesoid X receptor (FXR) agonist GW4064.

Starting from the known FXR agonist GW 4064 1a, a series of alternately 3,5-substituted isoxazoles was prepared. Several of these analogs were potent full FXR agonists. A subset of this series, with a tether between the isoxazole ring and the 3-position aryl substituent, were equipotent FXR agonists to GW 4064 1a, with the 2,6-dimethyl phenol analog 1t having greater FRET FXR potency than GW 4064 1a.

FXR agonist activity of conformationally constrained analogs of GW 4064.

Two series of conformationally constrained analogs of the FXR agonist GW 4064 1 were prepared. Replacement of the metabolically labile stilbene with either benzothiophene or naphthalene rings led to the identification of potent full agonists 2a and 2g.

Thiol-based angiotensin-converting enzyme 2 inhibitors: P1' modifications for the exploration of the S1' subsite.

Explorations of the S(1') subsite of ACE2 via modifications of the P(1') methylene biphenyl moiety of thiol-based metalloprotease inhibitors led to improvements in ACE2 selectivity versus ACE and NEP, while maintaining potent ACE2 inhibition.

Thiol-based angiotensin-converting enzyme 2 inhibitors: P1 modifications for the exploration of the S1 subsite.

Screening of a metalloprotease library led to the identification of a thiol-based dual ACE/NEP inhibitor as a potent ACE2 inhibitor. Modifications of the P(1) benzyl moiety led to improvements in ACE2 potency as well as to increased selectivity versus ACE and NEP.

Discovery of small molecule agonists for the bombesin receptor subtype 3 (BRS-3) based on an omeprazole lead.

Starting from a weak omeprazole screening hit, replacement of the pyridine with a 1,3-benzodioxole moiety, modification of the thioether linkage, and substitution of the benzimidazole pharmacophore led to the discovery of nanomolar BRS-3 agonists.

Conformationally constrained farnesoid X receptor (FXR) agonists: Naphthoic acid-based analogs of GW 4064.

Starting from the known FXR agonist GW 4064 1a, a series of stilbene replacements were prepared. The 6-substituted 1-naphthoic acid 1b was an equipotent FXR agonist with improved developability parameters relative to 1a. Analog 1b also reduced the severity of cholestasis in the ANIT acute cholestatic rat model.

Biarylaniline phenethanolamines as potent and selective beta3 adrenergic receptor agonists.

The synthesis of a series of phenethanolamine aniline agonists that contain an aniline ring on the right-hand side of the molecule substituted at the meta position with a benzoic acid or a pyridyl carboxylate is described. Several of the analogues (e.g., 34, 36-38, 40, and 44) have high beta(3) adrenergic receptor (AR) potency and selectivity against beta(1) and beta(2) ARs in Chinese hamster ovary (CHO) cells expressing beta ARs. The dog pharmacokinetic profile of some of these analogues showed >25% oral bioavailability and po half-lives of at least 1.5 h. Among the compounds described herein, the 3,3'-biarylaniline carboxylate derivatives 36, 38 and the phenylpyridyl derivative 44 demonstrated outstanding in vitro properties and reasonable dog pharmacokinetic profiles. These three analogues also showed dose dependent beta(3) AR mediated responses in mice. The ease of synthesis and superior dog pharmacokinetics of compound 38 relative to that of 44 in combination with its in vitro profile led us to choose this compound as a development candidate for the treatment of type 2 diabetes.

Design of cathepsin K inhibitors for osteoporosis.

Osteoporosis is a progressive, debilitating bone disease resulting in increased cost and morbidity to the elderly. This review summarizes the therapeutic approaches taken in the treatment of osteoporosis with particular emphasis on cathepsin K inhibitors. Cathepsin K, a cysteine protease predominantly expressed in osteoclasts, is a key player involved in bone matrix degradation. Both genetic ablation and small molecule inhibitor strategies versus cathepsin K have validated the importance of this enzyme in bone resorption. Starting from aldehyde-based leads, this review synopsizes the design of improved small molecule inhibitors by GlaxoWellcome researchers. These efforts involved the evaluation of various warheads, including cyanamides, ketoheterocycles, and ketoamides. Initial structure/activity relationships of aldehyde-based inhibitors proved useful in the design of ketoamide-based cathepsin K inhibitors. Further exploration of S(3), S(2), S(1), and S(1') subsites with P(3), P(2), P(1), and P(1') probes have resulted in the identification of potent, selective, orally bioavailable ketoamide-based inhibitors of cathepsin K with demonstrated in vivo efficacy.

Discovery of 4-Amino-8-quinoline Carboxamides as Novel, Submicromolar Inhibitors of NAD-Hydrolyzing Enzyme CD38.

Starting from the micromolar 8-quinoline carboxamide high-throughput screening hit 1a, a systematic exploration of the structure-activity relationships (SAR) of the 4-, 6-, and 8-substituents of the quinoline ring resulted in the identification of approximately 10-100-fold more potent human CD38 inhibitors. Several of these molecules also exhibited pharmacokinetic parameters suitable for in vivo animal studies, including low clearances and decent oral bioavailability. Two of these CD38 inhibitors, 1ah and 1ai, were shown to elevate NAD tissue levels in liver and muscle in a diet-induced obese (DIO) C57BL/6 mouse model. These inhibitor tool compounds will enable further biological studies of the CD38 enzyme as well as the investigation of the therapeutic implications of NAD enhancement in disease models of abnormally low NAD.

Discovery, Synthesis, and Biological Evaluation of Thiazoloquin(az)olin(on)es as Potent CD38 Inhibitors.

A series of thiazoloquin(az)olinones were synthesized and found to have potent inhibitory activity against CD38. Several of these compounds were also shown to have good pharmacokinetic properties and demonstrated the ability to elevate NAD levels in plasma, liver, and muscle tissue. In particular, compound 78c was given to diet induced obese (DIO) C57Bl6 mice, elevating NAD > 5-fold in liver and >1.2-fold in muscle versus control animals at a 2 h time point. The compounds described herein possess the most potent CD38 inhibitory activity of any small molecules described in the literature to date. The inhibitors should allow for a more detailed assessment of how NAD elevation via CD38 inhibition affects physiology in NAD deficient states.

Ketoamide-based inhibitors of cysteine protease, cathepsin K: P3 modifications.

Osteoporosis is a disease characterized by skeletal fragility. Cathepsin K, a lysosomal cysteine protease, has been implicated in the osteoclast mediated bone resorption. Inhibitors of this protease could potentially treat this skeletal disease. The present work describes exploration of the spatial requirements of the S3 subsite by the use of various sterically demanding P3 substituents. Sulfur and oxygen linked heterocycles as well as those without heteroatom linkers were found to provide potent inhibitors of cathepsin K. Representative examples from these series also afforded quite good selectivity ratios against most cathepsins tested. The tolerability of the S3 subsite for sterically demanding groups that provide potency and selectivity enhances the attractiveness of P3 changes to improve the physiochemical properties of inhibitors in the developments of compounds for the treatment of osteoporosis.

Potent and selective ketoamide-based inhibitors of cysteine protease, cathepsin K.

Cathepsin K, a lysosomal cysteine protease of the papain superfamily, is abundantly and selectively expressed in osteoclasts, suggesting that this enzyme is crucial for bone resorption. Prevention of osteoclast-mediated bone resorption via inhibition of cathepsin K could be an effective approach to prevent osteoporosis. Potent and selective reversible ketoamide-based inhibitors have been identified in the present study. Using a known crystal structure of a ketoamide-based inhibitor, information from residues that form the P2/P3 pocket was used in the design of inhibitors that could allow for gains in selectivity and potency. Further, incorporation of P' selective heterocycles, along with the P2/P3 modifications, is also described. These modifications have resulted in potent and selective cathepsin K inhibitors that allow for improvements in their physiochemical properties and represent a viable lead series for the discovery of new therapies for the prevention and treatment of osteoporosis

Design of potent, selective, and orally bioavailable inhibitors of cysteine protease cathepsin k.

Osteoclast-mediated bone matrix resorption has been attributed to cathepsin K, a cysteine protease of the papain family that is abundantly and selectively expressed in osteoclast. Inhibition of cathepsin K could potentially be an effective method to prevent osteoporosis. Structure-activity studies on a series of reversible ketoamides based inhibitors of cathepsin K have led to identification of potent and selective compounds. Crystallographic studies have given insights into the mode of binding of these inhibitors. A series of ketoamides with varying P1 moieties were first synthesized to find an optimum group that would fit into the S1 subsite of the cysteine protease, cathepsin K. With a desired P1 group in place a variety of heterocyclic analogues in the P' region were synthesized to study their steric and electronic effects. In the process of exploring these P' heterocyclic variations, excellent selectivity was gained over other highly homologous cysteine proteases, including cathepsins L, S, and V. The favorable pharmacokinetic properties of some of these cathepsin K inhibitors in rats make them suitable for evaluation in rodent osteoporosis models. A representative cathepsin K inhibitor was shown to attenuate PTH-stimulated hypercalcemia in the TPTX rat model. These inhibitors provide a viable lead series in the discovery of new therapies for the prevention and treatment of osteoporosis