System Setup. The high-resolution crystal structure of the OX1R in complex with suvorexant (PDB: 6TO7 ( )) was employed for docking and FEP calculations. This choice was based on its detailed representation of water molecules within the orthosteric binding pocket and the structural similarity of the ligand to compounds JH112, 1e, and 1f. Prior research has demonstrated the critical role of these water molecules in achieving accurate FEP results at the OX2R . The receptor preparation involved extracting coordinates for the receptor, water molecules, a sodium ion, and the ligand from chain A. Any introduced mutations were reverted, and the missing amino acid residue at position Q246 5.69 was modeled using PyMOL . Subsequent preparation steps were carried out using the Protein Preparation Wizard (47) module of the Schrödinger Suite 2021.3. This process included modeling missing side chains, removing water molecules located further than 5 Å from the ligand, optimizing hydrogen bonds, and setting protein protonation states at pH 7.4. Notably, the protonation states of histidines H216 5.39 and H344 7.39 were adjusted due to their proximity to aspartate D107 2.65 and glutamate E204 45.52 , respectively. Previous FEP studies highlighted the influence of histidine protonation on calculation accuracy .