Utilization of an Active Site Mutant Receptor for the Identification of Potent and Selective Atypical 5‑HT_2C Receptor Agonists

Agonism of the 5-HT_2C receptor represents one of the most well-studied and clinically proven mechanisms for pharmacological weight reduction. Selectivity over the closely related 5-HT_2A and 5-HT_2B receptors is critical as their activation has been shown to lead to undesirable side effects and major safety concerns. In this communication, we report the development of a new screening paradigm that utilizes an active site mutant D134A (D3.32) 5-HT_2C receptor to identify atypical agonist structures. We additionally report the discovery and optimization of a novel class of nonbasic heterocyclic amide agonists of 5-HT_2C. SAR investigations around the screening hits provided a diverse set of potent agonists at 5-HT_2C with high selectivity over the related 5-HT_2A and 5-HT_2B receptor subtypes. Further optimization through replacement of the amide with a variety of five- and six-membered heterocycles led to the identification of 6-(1-ethyl-3-(quinolin-8-yl)-1<i>H</i>-pyrazol-5-yl)­pyridazin-3-amine (<b>69</b>). Oral administration of <b>69</b> to rats reduced food intake in an ad libitum feeding model, which could be completely reversed by a selective 5-HT_2C antagonist

Discovery of Pyrrolidine-Containing GPR40 Agonists: Stereochemistry Effects a Change in Binding Mode

A novel series of pyrrolidine-containing GPR40 agonists is described as a potential treatment for type 2 diabetes. The initial pyrrolidine hit was modified by moving the position of the carboxylic acid, a key pharmacophore for GPR40. Addition of a 4-<i>cis</i>-CF₃ to the pyrrolidine improves the human GPR40 binding <i>K</i>_i and agonist efficacy. After further optimization, the discovery of a minor enantiomeric impurity with agonist activity led to the finding that enantiomers <b>(</b><i><b>R,R</b></i><b>)-68</b> and <b>(</b><i><b>S,S</b></i><b>)-68</b> have differential effects on the radioligand used for the binding assay, with <b>(</b><i><b>R,R</b></i><b>)-68</b> potentiating the radioligand and <b>(</b><i><b>S,S</b></i><b>)-68</b> displacing the radioligand. Compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b> activates both G_q-coupled intracellular Ca²⁺ flux and G_s-coupled cAMP accumulation. This signaling bias results in a dual mechanism of action for compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b>, demonstrating glucose-dependent insulin and GLP-1 secretion in vitro. In vivo, compound <b>(</b><i><b>R</b></i>,<i><b>R</b></i><b>)-68</b> significantly lowers plasma glucose levels in mice during an oral glucose challenge, encouraging further development of the series