Utilization of an Active Site Mutant Receptor for the Identification of Potent and Selective Atypical 5-HT Receptor Agonists.

Agonism of the 5-HT receptor represents one of the most well-studied and clinically proven mechanisms for pharmacological weight reduction. Selectivity over the closely related 5-HT and 5-HT 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 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. SAR investigations around the screening hits provided a diverse set of potent agonists at 5-HT with high selectivity over the related 5-HT and 5-HT 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)-1H-pyrazol-5-yl)pyridazin-3-amine (69). Oral administration of 69 to rats reduced food intake in an ad libitum feeding model, which could be completely reversed by a selective 5-HT antagonist.