Substituted tetrahydroisoquinolines as selective antagonists for the orexin 1 receptor

Increasing evidence implicates the orexin 1 (OX₁) receptor in reward processes, suggesting OX₁ antagonism could be therapeutic in drug addiction. In a program to develop an OX₁ selective antagonist, we designed and synthesized a series of substituted tetrahydroisoquinolines and determined their potency in OX₁ and OX₂ calcium mobilization assays. Structure-activity relationship (SAR) studies revealed limited steric tolerance and a preference for electron deficiency at the 7-position. Pyridylmethyl groups were shown to be optimal for activity at the acetamide position. Computational studies resulted in a pharmacophore model and confirmed the SAR results. Compound 72 significantly attenuated the development of place preference for cocaine in rats.