The serotonin 2A receptor (5-HT2AR) is responsible for the psychedelic effects of certain drugs, which show promise for treating neuropsychiatric conditions. This work examined how a series of compounds, including 25CN-NBOH, signal through two pathways: Gαq and β-arrestin. Disrupting the interaction with a specific amino acid, Ser1593×36, reduced both pathways' potency and efficacy, with Gαq signaling more strongly affected. This led to the creation of the first effective β-arrestin-biased 5-HT2AR agonists (4a-b and 6e-f), which prefer the β-arrestin pathway over Gαq relative to LSD.
Serotonergic psychedelics primarily activate the serotonin 2A receptor (5-HT2A), but the molecular basis for their psychedelic effects is not fully understood. A leading hypothesis is biased agonism, where certain signaling pathways are preferentially activated. This study tested a series of 4-position-substituted phenylalkylamines for their ability to recruit β-arrestin2 or miniGαq to the 5-HT2A receptor. All compounds acted as agonists with varying potency and efficacy. Lipophilicity of the 2C-X phenethylamines correlated more strongly with efficacy in the miniGαq assay than the β-arrestin2 assay. Molecular docking suggested that the 4-substituent fits into a hydrophobic pocket between transmembrane helices 4 and 5, potentially explaining this differential effect. Using serotonin and LSD as reference agonists, both benchmark and physiology bias were estimated, and qualitative structure-activity relationships remained consistent across different activation profiles.