Optical control of the β₂-adrenergic receptor with opto-prop-2: A cis-active azobenzene analog of propranolol

In this study, we synthesized and evaluated new photoswitchable ligands for the beta-adrenergic receptors β₁-AR and β₂-AR, applying an azologization strategy to the first-generation beta-blocker propranolol. The resulting compounds (Opto-prop-1, -2, -3) have good photochemical properties with high levels of light-induced trans-cis isomerization (>94%) and good thermal stability (t_1/2 > 10 days) of the resulting cis-isomer in an aqueous buffer. Upon illumination with 360-nm light to PSS_cis, large differences in binding affinities were observed for photoswitchable compounds at β₁-AR as well as β₂-AR. Notably, Opto-prop-2 (VUF17062) showed one of the largest optical shifts in binding affinities at the β₂-AR (587-fold, cis-active), as recorded so far for photoswitches of G protein-coupled receptors. We finally show the broad utility of Opto-prop-2 as a light-dependent competitive antagonist of the β₂-AR as shown with a conformational β₂-AR sensor, by the recruitment of downstream effector proteins and functional modulation of isolated adult rat cardiomyocytes.