Discovery of 1,3-disubstituted pyrazole peripheral cannabinoid receptor partial agonists.

Partial agonists of peripheral cannabinoid receptors (CBRs) have potential therapeutic applications in several medical conditions. However, (-)-trans-Δ9-tetrahydrocannabinol (THC), the principal active component of marijuana, which is a partial agonist of CB1 and CB2 penetrates the central nervous system (CNS) and produces adverse effects. Peripherally restricted partial agonists of CBRs, particularly of CB1, can be used to treat illnesses safely and effectively with a better therapeutic index. Here, we report on our efforts to synthesize pyrazole partial CBR agonists with peripheral selectivity, resulting in lead compound 40. This compound is a potent partial agonist of CB1 with âˆ¼ 5-fold higher plasma biodistribution over brain and represents an early lead for optimization.

Synthesis and characterization of an orally bioavailable small molecule agonist of the apelin receptor.

The apelin receptor (APJ) is a target for cardiovascular indications. Previously, we had identified a novel pyrazole-based agonist 1 ((S)-N-(1-(cyclobutylamino)-1-oxo-5-(piperidin-1-yl)pentan-3-yl)-1-cyclopentyl-5-(2,6-dimethoxyphenyl)-1H-pyrazole-3-carboxamide hydrochloride) of this GPCR. Systematic modification of 1 was performed to produce compounds with improved potency and ADME properties. Orally bioavailable compound 47 with favorable agonist potency (Ca2+EC50 = 24 nM, cAMPi EC50 = 6.5 nM) and pharmacokinetic properties (clearance ∼20 mL/min/kg in rats) was identified. This compound has vastly reduced brain penetration and is devoid of significant off-target liability. In summary, a potent and selective APJ agonist suitable for in vivo studies of APJ in peripheral tissues after oral administration has been identified.

Structure-Activity Relationship Development Efforts towards Peripherally Selective Analogs of the Cannabinoid Receptor Partial Agonist BAY 59-3074.

Selective modulation of peripheral cannabinoid receptors (CBRs) has potential therapeutic applications in medical conditions, including obesity, diabetes, liver diseases, GI disorders and pain. While there have been considerable efforts to produce selective antagonists or full agonists of CBRs, there has been limited reports on the development of partial agonists. Partial agonists targeting peripheral CBRs may have desirable pharmacological profiles while not producing centrally mediated dissociative effects. Bayer reported that BAY 59-3074 is a CNS penetrant partial agonist of both CB1 and CB2 receptors with efficacy in rat models of neuropathic and inflammatory pain. In this report, we demonstrate our efforts to synthesize analogs that would favor peripheral selectivity, while maintaining partial agonism of CB1. Our efforts led to the identification of a novel compound, which is a partial agonist of the human CB1 (hCB1) receptor with vastly diminished brain exposure compared to BAY 59-3074.

Identification of potent pyrazole based APELIN receptor (APJ) agonists.

The apelinergic system comprises the apelin receptor and its cognate apelin and elabela peptide ligands of various lengths. This system has become an increasingly attractive target for pulmonary and cardiometabolic diseases. Small molecule regulators of this receptor with good drug-like properties are needed. Recently, we discovered a novel pyrazole based small molecule agonist 8 of the apelin receptor (EC50 = 21.5 µM, Ki = 5.2 µM) through focused screening which was further optimized to initial lead 9 (EC50 = 0.800 µM, Ki = 1.3 µM). In our efforts to synthesize more potent agonists and to explore the structural features important for apelin receptor agonism, we carried out structural modifications at N1 of the pyrazole core as well as the amino acid side-chain of 9. Systematic modifications at these two positions provided potent small molecule agonists exhibiting EC50 values of <100 nM. Recruitment of ß-arrestin as a measure of desensitization potential of select compounds was also investigated. Functional selectivity was a feature of several compounds with a bias towards calcium mobilization over ß-arrestin recruitment. These compounds may be suitable as tools for in vivo studies of apelin receptor function.

Functionalized 6-(piperidin-1-yl)-8,9-diphenyl purines as inverse agonists of the CB1 receptor - SAR efforts towards selectivity and peripheralization.

Antagonists of type 1 cannabinoid receptors (CB1) may be useful in treating diabetes, hepatic disorders, and fibrosis. Otenabant (1) is a potent and selective CB1 inverse agonist that was under investigation as an anti-obesity agent, but its development was halted once adverse effects associated with another marketed inverse agonist rimonabant (2) became known. Non-tissue selective antagonists of CB1 that have high levels of brain penetration produce adverse effects in a small subset of patients including anxiety, depression and suicidal ideation. Currently, efforts are underway to produce compounds that have limited brain penetration. In this report, novel analogs of 1 are explored to develop and test strategies for peripheralization. The piperidine of 1 is studied as a linker, which is functionalized with alkyl, heteroalkyl, aryl and heteroaryl groups using a connector in the form of an amine, amide, sulfonamide, sulfamide, carbamate, oxime, amidine, or guanidine. We also report more polar replacements for the 4-chlorophenyl group in the 9-position of the purine core, which improve calculated physical properties of the molecules. These studies resulted in compounds such as 75 that are potent inverse agonists of hCB1 with exceptional selectivity for hCB1 over hCB2. SAR studies revealed ways to adjust physical properties to limit brain exposure.

Synthesis and pharmacological characterization of functionalized 6-piperazin-1-yl-purines as cannabinoid receptor 1 (CB1) inverse agonists.

Antagonists of peripheral type 1 cannabinoid receptors (CB1) may have utility in the treatment of obesity, liver disease, metabolic syndrome and dyslipidemias. We have targeted analogues of the purine inverse agonist otenabant (1) for this purpose. The non-tissue selective CB1 antagonist rimonabant (2) was approved as a weight-loss agent in Europe but produced centrally mediated adverse effects in some patients including dysphoria and suicidal ideation leading to its withdrawal. Efforts are now underway to produce compounds with limited brain exposure. While many structure-activity relationship (SAR) studies of 2 have been reported, along with peripheralized compounds, 1 remains relatively less studied. In this report, we pursued analogues of 1 in which the 4-aminopiperidine group was switched to piperazine group to enable a better understanding of SAR to eventually produce compounds with limited brain penetration. To access a binding pocket and modulate physical properties, the piperazine was functionalized with alkyl, heteroalkyl, aryl and heteroaryl groups using a variety of connectors, including amides, sulfonamides, carbamates and ureas. These studies resulted in compounds that are potent antagonists of hCB1 with high selectivity for hCB1 over hCB2. The SAR obtained led to the discovery of 65 (Ki = 4 nM, >1,000-fold selective for hCB1 over hCB2), an orally bioavailable aryl urea with reduced brain penetration, and provides direction for discovering peripherally restricted compounds with good in vitro and in vivo properties.

Discovery of a novel small molecule agonist scaffold for the APJ receptor.

The apelinergic system includes a series of endogenous peptides apelin, ELABELA/TODDLER and their 7-transmembrane G-protein coupled apelin receptor (APJ, AGTRL-1, APLNR). The APJ receptor is an attractive therapeutic target because of its involvement in cardiovascular diseases and potentially other disorders including liver fibrosis, obesity, diabetes, and neuroprotection. To date, pharmacological characterization of the APJ receptor has been limited due to the lack of small molecule functional agonists or antagonists. Through focused screening we identified a drug-like small molecule agonist hit 1 with a functional EC50 value of 21.5±5µM and binding affinity (Ki) of 5.2±0.5µM. Initial structure-activity studies afforded compound 22 having a 27-fold enhancement in potency and the first sub-micromolar full agonist with an EC50 value of 800±0.1nM and Ki of 1.3±0.3µM. Preliminary SAR, synthetic methodology, and in vitro pharmacological characterization indicate this scaffold will serve as a favorable starting point for further refinement of APJ potency and selectivity.

Discovery and Characterization of the First Nonpeptide Antagonists for the Relaxin-3/RXFP3 System.

The neuropeptide relaxin-3/RXFP3 system is involved in many important physiological processes such as stress responses, appetite control, and motivation for reward. To date, pharmacological studies of RXFP3 have been limited to peptide ligands. In this study, we report the discovery of the first small-molecule antagonists of RXFP3 through a high-throughput screening campaign. Focused structure-activity relationship studies of the hit compound resulted in RLX-33 (33) that was able to inhibit relaxin-3 activity in a battery of functional assays. RLX-33 is selective for RXFP3 over RXFP1 and RXFP4, two related members in the relaxin/insulin superfamily, and has favorable pharmacokinetic properties for behavioral assessment. When administered to rats intraperitoneally, RLX-33 blocked food intake induced by the RXFP3-selective agonist R3/I5. Collectively, our findings demonstrated that RLX-33 represents a promising antagonist scaffold for the development of drugs targeting the relaxin-3/RXFP3 system.

Indole-Containing Amidinohydrazones as Nonpeptide, Dual RXFP3/4 Agonists: Synthesis, Structure-Activity Relationship, and Molecular Modeling Studies.

The central relaxin-3/RXFP3 system plays important roles in stress responses, feeding, and motivation for reward. However, exploration of its therapeutic applications has been hampered by the lack of small molecule ligands and the cross-activation of RXFP1 in the brain and RXFP4 in the periphery. Herein, we report the first structure-activity relationship studies of a series of novel nonpeptide amidinohydrazone-based agonists, which were characterized by RXFP3 functional and radioligand binding assays. Several potent and efficacious RXFP3 agonists (e.g., 10d) were identified with EC50 values <10 nM. These compounds also had high potency at RXFP4 but no agonist activity at RXFP1, demonstrating > 100-fold selectivity for RXFP3/4 over RXFP1. In vitro ADME and pharmacokinetic assessments revealed that the amidinohydrazone derivatives may have limited brain permeability. Collectively, our findings provide the basis for further optimization of lead compounds to develop a suitable agonist to probe RXFP3 functions in the brain.

Pyrazole Agonist of the Apelin Receptor Improves Symptoms of Metabolic Syndrome in Mice.

Apelin receptor agonism improves symptoms of metabolic syndrome. However, endogenous apelin peptides have short half-lives, making their utility as potential drugs limited. Previously, we had identified a novel pyrazole-based agonist scaffold. Systematic modification of this scaffold was performed to produce compounds with improved ADME properties. Compound 13 with favorable agonist potency (cAMPi EC50 = 162 nM), human liver microsome stability (T1/2 = 62 min), and pharmacokinetic profile in rodents was identified. The compound was tested in a mouse model of diet-induced obesity (DIO) and metabolic syndrome for efficacy. Treatment with 13 led to significant weight loss, hypophagia, improved glucose utilization, reduced liver steatosis, and improvement of disease-associated biomarkers. In conclusion, a small-molecule agonist of the apelin receptor has been identified that is suitable for in vivo investigation of the apelinergic system in DIO and perhaps other diseases where this receptor has been implicated to play a role.

Functionalized 6-(Piperidin-1-yl)-8,9-Diphenyl Purines as Peripherally Restricted Inverse Agonists of the CB1 Receptor.

Peripherally restricted CB1 receptor antagonists may be useful in treating metabolic syndrome, diabetes, liver diseases, and gastrointestinal disorders. Clinical development of the centrally acting CB1 inverse agonist otenabant (1) was halted due to its potential of producing adverse effects. SAR studies of 1 are reported herein with the objective of producing peripherally restricted analogues. Crystal structures of hCB1 and docking studies with 1 indicate that the piperidine group could be functionalized at the 4-position to access a binding pocket that can accommodate both polar and nonpolar groups. The piperidine is studied as a linker, functionalized with alkyl, heteroalkyl, aryl, and heteroaryl groups using a urea connector. Orally bioavailable and peripherally selective compounds have been produced that are potent inverse agonists of hCB1 with exceptional selectivity for hCB1 over hCB2. Compound 38 blocked alcohol-induced liver steatosis in mice and has good ADME properties for further development.

Blocking Alcoholic Steatosis in Mice with a Peripherally Restricted Purine Antagonist of the Type 1 Cannabinoid Receptor.

Type 1 cannabinoid receptor (CB1) antagonists have demonstrated promise for the treatment of obesity, liver disease, metabolic syndrome, and dyslipidemias. However, the inhibition of CB1 receptors in the central nervous system can produce adverse effects, including depression, anxiety, and suicidal ideation. Efforts are now underway to produce peripherally restricted CB1 antagonists to circumvent CNS-associated undesirable effects. In this study, a series of analogues were explored in which the 4-aminopiperidine group of compound 2 was replaced with aryl- and heteroaryl-substituted piperazine groups both with and without a spacer. This resulted in mildly basic, potent antagonists of human CB1 (hCB1). The 2-chlorobenzyl piperazine, 25, was found to be potent ( Ki = 8 nM); to be >1000-fold selective for hCB1 over hCB2; to have no hERG liability; and to possess favorable ADME properties including high oral absorption and negligible CNS penetration. Compound 25 was tested in a mouse model of alcohol-induced liver steatosis and found to be efficacious. Taken together, 25 represents an exciting lead compound for further clinical development or refinement.