Effect of 1-substitution on tetrahydroisoquinolines as selective antagonists for the orexin-1 receptor
Perrey, D. A., German, N. A., Decker, A. M., Thorn, D., Li, J-X., Gilmour, B. P., Thomas, B. F., Harris, D. L., Runyon, S. P., & Zhang, Y. (2015). Effect of 1-substitution on tetrahydroisoquinolines as selective antagonists for the orexin-1 receptor. ACS Chemical Neuroscience, 6(4), 599-614. https://doi.org/10.1021/cn500330v
Selective blockade of the orexin-1 receptor (OX1) has been suggested as a potential approach to drug addiction therapy because of its role in modulating the brain's reward system. We have recently reported a series of tetrahydroisoquinoline-based OX1 selective antagonists. Aimed at elucidating structure-activity relationship requirements in other regions of the molecule and further enhancing OX1 potency and selectivity, we have designed and synthesized a series of analogues bearing a variety of substituents at the 1-position of the tetrahydroisoquinoline. The results show that an optimally substituted benzyl group is required for activity at the OX1 receptor. Several compounds with improved potency and/or selectivity have been identified. When combined with structural modifications that were previously found to improve selectivity, we have identified compound 73 (RTIOX-251) with an apparent dissociation constant (K-e) of 16.1 nM at the OX1 receptor and >620-fold selectivity over the OX2 receptor. In vivo, compound 73 was shown to block the development of locomotor sensitization to cocaine in rats.