New 5-HT2C receptor agonists

Novel serotonin receptor 2 (5-HT2R) agonists and antagonists: a patent review (2004-2014)

INTRODUCTION

Serotonin or 5-hydroxytryptamine (5-HT) is a substance found in plasma, which increases smooth muscle contraction and mediates platelet aggregation. In addition, it is a monoamine neurotransmitter and is implicated in diverse behaviors. The serotonin receptor 2 (5-HT2) subfamily is best known for biased signaling and is strongly expressed mainly in the brain regions postulated to be involved in the modulation of higher cognitive and affective functions. Modulators of the 5-HT2 receptor are currently used to treat a variety of diseases including chronic pain and psychonosema. These properties suggest that 5-HT2 receptors may become an important therapeutic target for the treatment of various pathological conditions.

AREAS COVERED

This review highlights the significant progress that has been made in the discovery and development of 5-HT2 receptor agonists and antagonists based on an analysis of the patent literature between January 2004 and December 2014.

EXPERT OPINION

Cumulative evidence over the past decade supports the notion that the modulation of 5-HT2 receptors has a positive effect on human cognition and emotion. Therefore, we suggest that new agonists and antagonists may play an important role in the treatment of disorders such as schizophrenia, addiction and obesity.

Regioselective alkylation of 1,3,4,5-tetrahydrobenzo[d]azepin-2-one and biological evaluation of the resulting alkylated products as potentially selective 5-HT₂c agonists

The benzazepine ring system has offered interesting CNS-active medicinal agents. Taking this privileged structure as the basic scaffold, [Formula: see text] and/or [Formula: see text]-alkylated benzazepin-2-one derivatives and their reduced analogs have been prepared as potential [Formula: see text] receptor agonists. The selective alkylation at the [Formula: see text] and/or [Formula: see text] positions of this seven-membered lactam ring is here reported for the first time under different reaction conditions. The synthesized compounds were evaluated for their biological profile as potential [Formula: see text] agonists using a classic pharmacological approach. Three derivatives (15, 17, and 20) have shown promising [Formula: see text] agonistic activity which can be further optimized as anti-obesity agents for the treatment of male sexual dysfunction. Further, a homology model for [Formula: see text] receptor was generated using MODELLER, and ligand-receptor interactions for these potential molecules were studied.

In vitro and in vivo activities of 2-aminopyrazines and 2-aminopyridines in experimental models of human African trypanosomiasis

New drugs for the treatment of human African trypanosomiasis are urgently needed. A number of 2-aminopyrazines/2-aminopyridines were identified as promising leads following a focused screen of 5,500 compounds for Trypanosoma brucei subsp. brucei viability. Described compounds are trypanotoxic in the submicromolar range and show comparably low cytotoxicity on representative mammalian cell lines. Specifically, 6-([6-fluoro-3,4-dihydro-2H-1-benzopyran-4-yl)]oxy)-N-(piperidin-4-yl)pyrazin-2-amine (CBK201352) is trypanotoxic for T. brucei subsp. brucei, T. brucei subsp. gambiense, and T. brucei subsp. rhodesiense and is nontoxic to mammalian cell lines, and in vitro preclinical assays predict promising pharmacokinetic parameters. Mice inoculated intraperitoneally (i.p.) with 25 mg/kg CBK201352 twice daily for 10 days, starting on the day of infection with T. brucei subsp. brucei, show complete clearance of parasites for more than 90 days. Thus, CBK201352 and related analogs are promising leads for the development of novel treatments for human African trypanosomiasis.

Design and synthesis of pyridazinone-based 5-HT(2C) agonists

The SAR of a series of pyridazinone derived 5-HT(2C) agonists has been explored and resulted in identification of a compound with excellent levels of 5-HT(2C) functional agonism and selectivity over 5-HT(2A) and 5-HT(2B). This compound displayed good in vivo efficacy in pre-clinical models of stress urinary incontinence, despite having physiochemical properties commensurate with impaired CNS penetration.

The design and synthesis of a tricyclic single-nitrogen scaffold that serves as a 5-HT2C receptor agonist

5-HT2C agonists have shown efficacy in limiting food consumption and thus may serve as an important drug class in combating obesity. We describe the design and synthesis of a novel tricyclic single-nitrogen scaffold that was used to produce 5-HT2C agonists. SAR was developed around this chemotype and compounds were identified that were potent (Ki<15 nM) and selective relative to other 5-HT2 receptors. The most promising compound displayed a good pharmacokinetic profile in multiple animal species, and was efficacious in an acute feeding study in rats.

The identification of pyrimidine-diazabicyclo[3.3.0]octane derivatives as 5-HT2C receptor agonists

The 5-HT2C receptor has been implicated in the regulation of appetite. As such, small molecule agonists to this receptor may serve as novel therapies to combat obesity. We describe here the identification, synthesis, and SAR of a 5-HT2C agonist from a unique pyrimidine-diazabicyclo[3.3.0]octane series. This compound displayed good potency at the 5-HT2C receptor, modest selectivity relative to other 5-HT2 receptors, and was efficacious in an acute feeding study in rats.

The potential use of selective 5-HT2C agonists in treating obesity

Activation of central 5-HT2C receptors as a strategy for appetite suppression and weight control is supported by animal pharmacology and human clinical studies. Considerable evidence comes from the weight-loss effects of fenfluramine, a non-selective 5-HT2C agonist. Advances in molecular pharmacology have led to an understanding of the effects of 5-HT2C receptor activation on food intake and satiety, in addition to providing insight into the causes of cardiac valvular insufficiency and pulmonary hypertension associated with the use of fenfluramine. However, clinically validated animal models of drug-induced disease and knowledge of the molecular mechanisms of these safety issues is lacking. For this reason, the development of selective 5-HT2C agonists for the treatment of obesity has remained a challenge.

Differential expression of 5-HT2A and 5-HT2C receptor mRNAs in mice prone, or resistant, to chronic high-fat diet-induced obesity

The present study examined the levels of 5-HT(2A) and 5-HT(2C) (2A and 2C receptors of 5-hydroxytryptamine; serotonin) receptor messenger RNA (mRNA) expressions in the brain of chronic high-fat diet-induced obese (DIO) and obese-resistant (DR) mice. Thirty-one mice were used in this study. Twenty-four mice were fed with a high-fat diet (HF: 40% of calories from fat) for 4 weeks and then classified as the DIO (n = 8) or DR (n = 8) mice according to the highest and lowest body weight (BW) gainers. Seven mice were placed on a low-fat diet (LF: 10% of calories from fat) and were used as controls. After 20 weeks of feeding, the visceral fat accumulation was 620 +/- 42 mg in the DIO group versus 198 +/- 89 mg in the DR and 84 +/- 18 mg in the LF groups. Using quantitative in situ hybridization techniques, levels of 2A and 2C serotonin (5-HT) receptor mRNAs were measured in multiple brain sections of mice from the three groups. Most regions did not differ between groups but, importantly, the DIO mice had a significantly higher level of 5-HT(2A) receptor mRNA expression in the olfactory nucleus (Olf) compared to the DR and LF mice (+30% and +37%, respectively). The levels of Olf 5-HT(2A) receptor mRNA expression were related to body fat mass. The level of 5-HT(2C) mRNA receptor expression in the ventromedial hypothalamic (VMH) nucleus was 40% higher in the DIO mice than in the LF mice. Furthermore, the 5-HT(2C) receptor mRNA expression in the posterodorsal part of the medial amygdaloid (MePD) nucleus was 25% higher in the DIO mice than in the DR mice. The level of VMH 5-HT(2C) receptor mRNA expression was correlated with body fat mass. In conclusion, this study has demonstrated differentially regulated levels of the 5-HT(2A) and 5-HT(2C) receptor mRNA expressions in the specific brain regions of the DIO and DR mice. It provides neural anatomical bases that the 5-HT(2C) receptors positively influence satiety center (VMH) while the 5-HT(2A) receptor regulates olfactory sensory effects. The findings also assist us to understand the role of these receptors in mice susceptible or resistant to diet-induced obesity.