Discovery of novel orexin receptor antagonists using a 1,3,5-trioxazatriquinans bearing multiple effective residues (TriMER) library

Structurally diverse small compounds are utilized to obtain hit compounds that have suitable pharmacophores in appropriate three-dimensional conformations for the target drug receptors. We have focused on the 1,3,5-trioxazatriquinane skeleton, which has a high degree of three-dimensional properties, leading to a novel small-scale focused library based on 1,3,5- trioxazatriquinane. In the library screening for the orexin receptor, some of the compounds showed orexin receptor antagonistic activity with a high hit rate of 7%. By optimizing the hit compounds, we discovered a potent dual orexin receptor antagonist, 38b, and a selective orexin 1 receptor antagonist, 41b carrying the same plane structure. Both compounds showed reasonable brain permeability and beneficial effects when administered intraperitoneally to wild-type mice. Docking simulations of their eutomers, (–)-38b and (+)-41b, with orexin receptors suggested that the interaction between the 1,3,5-trioxazatriquinane core structure and the hydrophobic subpocket in orexin receptors enables a U-shape structure, which causes tight van der Waals interactions with the receptors similar to SB-334867, a selective orexin 1 receptor antagonist. These results indicate that the 1,3,5-trioxazatriquinanes bearing multiple effective residues (TriMERs) could serve as a privileged structure for G-protein coupled receptors (GPCRs) and the TriMER library approach might be useful for the hit discovery process targeting other GPCRs not only opioid and orexin receptors.