Synthetic Studies of Neoclerodane Diterpenes from Salvia divinorum: Design, Synthesis, and Evaluation of Analogues with Improved Potency and G-protein Activation Bias at the μ Opioid Receptor

A series of analogues of kurkinorin, a non-nitrogenous μ opioid receptor (MOR) agonist derived from salvinorin A, were synthesized and tested in vitro for G-protein activation and β-arrestin-2 recruitment. Some compounds showed biased signaling, either toward β-arrestin-2 or G-protein activation. Compound 25 is a potent MOR-selective agonist with G-protein bias, over 100 times more potent than morphine and over 5 times more potent than fentanyl in vitro, and produces antinociception with limited tolerance development in vivo, despite lacking a basic nitrogen or other ionizable groups typical of opioid ligands.

Study at a glance

Abstract

Previous structure-activity relationship (SAR) studies identified the first centrally-acting, non-nitrogenous μ opioid receptor (MOR) agonist, kurkinorin (1), derived from salvinorin A. In an effort to further probe the physiological effects induced upon activation of MORs with this non-morphine scaffold, a variety of analogues were synthesized and evaluated in vitro for their ability to activate G-proteins and recruit β-arrestin-2 upon MOR activation. Through these studies, compounds that are potent agonists at MORs and either biased towards β-arrestin-2 recruitment or biased towards G-protein activation have been identified. One such compound, 25, has potent activity and selectivity at the MOR over KOR with bias for G-protein activation. Impressively, 25 is over 100x more potent than morphine and over 5x more potent than fentanyl in vitro and elicits antinociception with limited tolerance development in vivo. This is especially significant given that 25 lacks a basic nitrogen and other ionizable groups present in other opioid ligand classes.