Identification of MK-5710 ((8aS)-8a-methyl-1,3-dioxo-2-[(1S,2R)-2-phenylcyclopropyl]-N-(1-phenyl-1H-pyrazol-5-yl)hexahydroimid azo[1,5-a]pyrazine-7(1H)-carboxamide), a potent smoothened antagonist for use in Hedgehog pathway dependent malignancies, part 1

The Hedgehog (Hh-) signaling pathway is a key developmental pathway which controls patterning, growth and cell migration in most tissues, but evidence has accumulated showing that many human tumors aberrantly reactivate this pathway. Smoothened antagonists offer opportunities for the treatment of malignancies dependent on the Hh pathway, and the most advanced clinical candidates are demonstrating encourage initial results. A novel series of [6,5]-bicyclic tetrahydroimidazo[1,5-a]pyrazine-1,3(2H,5H)-dione smoothened antagonists has been identified, and the series has been extensively explored to ascertain the key detriments for activity, demonstrating that the trans-2-phenylcyclopropyl and hydantoin ring systems are critical for potency, while a variety of urea substituents can be tolerated. The combination of these optimal groups gives smoothened antagonists with activity in the low nanomolar range.     

Identification of a series of 4-[3-(quinolin-2-yl)-1,2,4-oxadiazol-5-yl]piperazinyl ureas as potent smoothened antagonist hedgehog pathway inhibitors

The Hedgehog (Hh-) signalling pathway is a key developmental pathway and there is a growing body of evidence showing that this pathway is aberrantly reactivated in a number of human tumors. Novel agents capable of inhibiting this pathway are sought, and an entirely novel series of smoothened (Smo) antagonists capable of inhibiting the pathway have been identified through uHTS screening. Extensive exploration of the scaffold identified the key functionalities necessary for potency, enabling potent nanomolar Smo antagonists like 91 and 94 to be developed. Optimization resulted in the most advanced compounds displaying low serum shift, clean off-targets profile, and moderate clearance in both rats and dogs. These compounds are valuable tools with which to probe the biology of the Hh-pathway.     

N-(2-alkylaminoethyl)-4-(1,2,4-oxadiazol-5-yl)piperazine-1-carboxamides as highly potent smoothened antagonists

Smoothened (Smo) antagonists are emerging as new therapies for the treatment of neoplasias with aberrantly reactivated hedgehog (Hh) signaling pathway. A novel series of 4-[3-(quinolin-2-yl)-1,2,4-oxadiazol-5-yl]piperazinyl ureas as smoothened antagonists was recently described, herein the series has been further optimized through the incorporation of a basic amine into the urea. This development resulted in identification of some exceptionally potent smoothened antagonists with low serum shifts, however, reductive ring opening on the 1,2,4-oxadiazole in rats limits the applicability of these compounds in in vivo studies.     

Discovery of [1,2,4]triazolo[4,3-a]pyridines as potent Smoothened inhibitors targeting the Hedgehog pathway with improved antitumor activity in vivo

Triple-negative breast cancer (TNBC), a subset of breast cancers, have poorer survival than other breast cancer types. Recent studies have demonstrated that the abnormal Hedgehog (Hh) pathway is activated in TNBC and that these treatment-resistant cancers are sensitive to inhibition of the Hh pathway. Smoothened (Smo) protein is a vital constituent in Hh signaling and an attractive drug target. Vismodegib (VIS) is one of the most widely studied Smo inhibitors. But the clinical application of Smo inhibitors is limited to adult patients with BCC and AML, with many side effects. Therefore, it’s necessary to develop novel Smo inhibitor with better profiles. Twenty [1,2,4]triazolo[4,3-a]pyridines were designed, synthesized and screened as Smo inhibitors. Four of these novel compounds showed directly bound to Smo protein with stronger binding affinity than VIS. The new compounds showed broad anti-proliferative activity against cancer cell lines in vitro, especially triple-negative breast cancer cells. Mechanistic studies demonstrated that TPB15 markedly induced cell cycle arrest and apoptosis in MDA-MB-468 cells. TPB15 blocked Smo translocation into the cilia and reduced Smo protein and mRNA expression. Furthermore, the expression of the downstream regulatory factor glioma-associated oncogene 1 (Gli1) was significantly inhibited. Finally, TPB15 demonstrated greater anti-tumor activity in our animal models than VIS with lower toxicity. Hence, these results support further optimization of this novel scaffold to develop improved Smo antagonists.     

Amine-free melanin-concentrating hormone receptor 1 antagonists: Novel 1-(1H-benzimidazol-6-yl)pyridin-2(1H)-one derivatives and design to avoid CYP3A4 time-dependent inhibition

Melanin-concentrating hormone (MCH) is an attractive target for antiobesity agents, and numerous drug discovery programs are dedicated to finding small-molecule MCH receptor 1 (MCHR1) antagonists. We recently reported novel pyridine-2(1H)-ones as aliphatic amine-free MCHR1 antagonists that structurally featured an imidazo[1,2-a]pyridine-based bicyclic motif. To investigate imidazopyridine variants with lower basicity and less potential to inhibit cytochrome P450 3A4 (CYP3A4), we designed pyridine-2(1H)-ones bearing various less basic bicyclic motifs. Among these, a lead compound 6a bearing a 1H-benzimidazole motif showed comparable binding affinity to MCHR1 to the corresponding imidazopyridine derivative 1. Optimization of 6a afforded a series of potent thiophene derivatives (6q–u); however, most of these were found to cause time-dependent inhibition (TDI) of CYP3A4. As bioactivation of thiophenes to form sulfoxide or epoxide species was considered to be a major cause of CYP3A4 TDI, we introduced electron withdrawing groups on the thiophene and found that a CF₃ group on the ring or a Cl adjacent to the sulfur atom helped prevent CYP3A4 TDI. Consequently, 4-[(5-chlorothiophen-2-yl)methoxy]-1-(2-cyclopropyl-1-methyl-1H-benzimidazol-6-yl)pyridin-2(1H)-one (6s) was identified as a potent MCHR1 antagonist without the risk of CYP3A4 TDI, which exhibited a promising safety profile including low CYP3A4 inhibition and exerted significant antiobesity effects in diet-induced obese F344 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.     

Discovery of 2-(1H-indazol-1-yl)-thiazole derivatives as selective EP1 receptor antagonists for treatment of overactive bladder by core structure replacement

We have designed a series of potent EP₁ receptor antagonists. These antagonists are a series of 2-(1H-indazol-1-yl)-thiazoles in which the core structure was replaced with pyrazole-phenyl groups. In preliminary conscious rat cystometry experiments, two representative candidates, 2 and 22, increased bladder capacity. In particular, the increase using 22 was approximately 2-fold that of the baseline. More detailed profiling of this compound and further optimization of this series promises to provide a novel class of drug for treating overactive bladder (OAB).     

The discovery of novel N-(2-pyrimidinylamino) benzamide derivatives as potent hedgehog signaling pathway inhibitors

Hedgehog signaling pathway inhibitors are emerging as new therapeutic intervention against cancer. A novel series of N-(2-pyrimidinylamino) benzamide derivatives as hedgehog signaling pathway inhibitors were designed and synthesized. Most compounds presented significant inhibitory effect on hedgehog signaling pathway, among which 21 compounds exhibited more potent than vismodegib. Furthermore, compound 6a showed moderate pharmacokinetic properties in vivo, representing a promising lead compound for further exploration.     

2-Aminopyrimidin-4(1H)-one as the novel bioisostere of urea: Discovery of novel and potent CXCR2 antagonists

2-Aminopyrimidin-4(1H)-one was proposed as the novel bioisostere of urea. Bioisosteric replacement of the reported urea series of the CXCR2 antagonists with 2-aminopyrimidin-4(1H)-ones led to the discovery of the novel and potent CXCR2 antagonist 3e. 2-Aminopyrimidin-4(1H)-one derivative 3e demonstrated a good developability profile (reasonable solubility and high permeability) and superior chemical stability especially in simulated gastric fluid (SGF) compared with ureas.     

Amine-free melanin-concentrating hormone receptor 1 antagonists: Novel non-basic 1-(2H-indazole-5-yl)pyridin-2(1H)-one derivatives and mitigation of mutagenicity in Ames test

To develop non-basic melanin-concentrating hormone receptor 1 (MCHR1) antagonists with a high probability of target selectivity and therapeutic window, we explored neutral bicyclic motifs that could replace the previously reported imidazo[1,2-a]pyridine or 1H-benzimidazole motif. The results indicated that the binding affinity of a chemically neutral 2H-indazole derivative 8a with MCHR1 (hMCHR1: IC₅₀ = 35 nM) was comparable to that of the imidazopyridine and benzimidazole derivatives (1 and 2, respectively) reported so far. However, 8a was positive in the Ames test using TA1537 in S9− condition. Based on a putative intercalation of 8a with DNA, we introduced a sterically-hindering cyclopropyl group on the indazole ring to decrease planarity, which led to the discovery of 1-(2-cyclopropyl-3-methyl-2H-indazol-5-yl)-4-{[5-(trifluoromethyl)thiophen-3-yl]methoxy}pyridin-2(1H)-one 8l without mutagenicity in TA1537. Compound 8l exerted significant antiobesity effects in diet-induced obese F344 rats and exhibited promising safety profile.     

Design and synthesis of novel 3-(benzo[d]oxazol-2-yl)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl)pyridin-2-amine derivatives as selective G-protein-coupled receptor kinase-2 and -5 inhibitors

G-protein-coupled receptor kinase (GRK)-2 and -5 are emerging therapeutic targets for the treatment of cardiovascular disease. In our efforts to discover novel small molecules to inhibit GRK-2 and -5, a class of compound based on 3-(benzo[d]oxazol-2-yl)-5-(1-(piperidin-4-yl)-1H-pyrazol-4-yl)pyridin-2-amine was identified as a novel hit by high throughput screening campaign. Structural modification of parent benzoxazole scaffolds by introducing substituents on phenyl displayed potent inhibitory activities toward GRK-2 and -5.     

Amine substituted N-(1H-benzimidazol-2ylmethyl)-5,6,7,8-tetrahydro-8-quinolinamines as CXCR4 antagonists with potent activity against HIV-1

Several novel amine substituted N-(1H-benzimidazol-2ylmethyl)-5,6,7,8-tetrahydro-8-quinolinamines were synthesized which had potent activity against HIV-1. The synthetic approaches adopted allowed for variation of the substitution pattern and resulting changes in antiviral activity are highlighted. This led to the identification of compounds with low and sub-nanomolar anti-HIV-1 activity.     

Discovery of 6-chloro-2-trifluoromethyl-7-aryl-7H-imidazo[1,2-a]imidazol-3-ylmethylamines,a novel class of corticotropin-releasing factor receptor type 1 (CRF1R) antagonists

A novel series of [6-chloro-2-trifluoromethyl-7-aryl-7H-imidazo[1,2-a]imidazol-3-ylmethyl]-dialkylamines was discovered as potent CRF₁R antagonists. The optimization of binding affinity in the series by the parallel reaction approach is discussed herein.     

Evolution of novel tricyclic CRTh2 receptor antagonists from a (E)-2-cyano-3-(1H-indol-3-yl)acrylamide scaffold

(E)-2-(3-(3-((3-Bromophenyl)amino)-2-cyano-3-oxoprop-1-en-1-yl)-1H-indol-1-yl)acetic acid (1) was discovered in a HTS campaign for CRTh2 receptor antagonists. An SAR around this hit could be established and representatives with interesting activity profiles were obtained. Ring closing tactics to convert this hit series into a novel 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole based CRTh2 receptor antagonist series is presented.     

Design,synthesis and biological evaluation of 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one derivatives as potent β2-adrenoceptor agonists

A series of novel β₂-adrenoceptor agonists with a 5-(2-amino-1-hydroxyethyl)-8-hydroxyquinolin-2(1H)-one moiety was designed, synthesized and evaluated for biological activity in human embryonic kidney 293 cells and isolated guinea pig trachea. Compounds 9g and (R)-18c exhibited the most excellent β₂-adrenoceptor agonistic effects and high β₂/β₁-selectivity with EC₅₀ values of 36 pM for 9g and 21 pM for (R)-18c. They produced potent airway smooth muscle relaxant effects with fast onset of action and long duration of action in an in vitro guinea pig trachea model of bronchodilation. These results support further development of the two compounds into drug candidates.     

Discovery and preclinical profile of teneligliptin (3-[(2S,4S)-4-[4-(3-methyl-1-phenyl-1H-pyrazol-5-yl)piperazin-1-yl]pyrrolidin-2-ylcarbonyl]thiazolidine): A highly potent,selective, long-lasting and orally active dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes

Dipeptidyl peptidase IV (DPP-4) inhibition is suitable mechanism for once daily oral dosing regimen because of its low risk of hypoglycemia. We explored linked bicyclic heteroarylpiperazines substituted at the γ-position of the proline structure in the course of the investigation of l-prolylthiazolidines. The efforts led to the discovery of a highly potent, selective, long-lasting and orally active DPP-4 inhibitor, 3-[(2S,4S)-4-[4-(3-methyl-1-phenyl-1H-pyrazol-5-yl)piperazin-1-yl]pyrrolidin-2-ylcarbonyl]thiazolidine (8g), which has a unique structure characterized by five consecutive rings. An X-ray co-crystal structure of 8g in DPP-4 demonstrated that the key interaction between the phenyl ring on the pyrazole and the S₂ extensive subsite of DPP-4 not only boosted potency, but also increased selectivity. Compound 8g, at 0.03 mg/kg or higher doses, significantly inhibited the increase of plasma glucose levels after an oral glucose load in Zucker fatty rats. Compound 8g (teneligliptin) has been approved for the treatment of type 2 diabetes in Japan.     

Discovery of 2-(4-((1H-1,2,4-triazol-1-yl)methyl)-5-(4-bromophenyl)-1-(2-chlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-thiadiazole (GCC2680) as a potent,selective and orally efficacious cannabinoid-1 receptor antagonist

Structure–activity relationship studies in a series of diarylpyrazolyl thiadiazoles identified cannabinoid-1 receptor antagonists with excellent potency and selectivity. Based on its exceptional in vivo efficacy in animal models and its favorable pharmacokinetic and toxicological profiles, 2-(4-((1H-1,2,4-triazol-1-yl)methyl)-5-(4-bromophenyl)-1-(2-chlorophenyl)-1H-pyrazol-3-yl)-5-tert-butyl-1,3,4-thiadiazole (GCC2680) was selected as a preclinical candidate for the treatment of obesity.     

Synthesis and SAR study of pyrrolo[3,4-b]pyridin-7(6H)-one derivatives as melanin concentrating hormone receptor 1 (MCH-R1) antagonists

The discovery and optimization of novel pyrrolo[3,4-b]pyridin-7(6H)-one MCH-R1 antagonists are described. A systematic SAR study probing the effects of aryl-, benzyl- and arylthio-substituents at the 2-position of the pyrrolo[3,4-b]pyridin-7(6H)-ones led to identification of the 2-[(4-fluorophenyl)thio] derivative 7b as a highly potent MCH-R1 antagonist. This compound also has favorable pharmacokinetic properties along with a high metabolic stability and a minimal impact on CYP isoforms and hERG.     

Discovery of 2-((1H-benzo[d]imidazol-1-yl)methyl)-4H-pyrido[1,2-a]pyrimidin-4-ones as novel PKM2 activators

The M2 isoform of pyruvate kinase is an emerging target for antitumor therapy. In this letter, we describe the discovery of 2-((1H-benzo[d]imidazol-1-yl)methyl)-4H-pyrido[1,2-a]pyrimidin-4-ones as potent and selective PKM2 activators which were found to have a novel binding mode. The original lead identified from high throughput screening was optimized into an efficient series via computer-aided structure-based drug design. Both a representative compound from this series and an activator described in the literature were used as molecular tools to probe the biological effects of PKM2 activation on cancer cells. Our results suggested that PKM2 activation alone is not sufficient to alter cancer cell metabolism.