Azi-medetomidine: Synthesis and Characterization of a Novel α2 Adrenergic Photoaffinity Ligand

Abstract

Agonists at the α2 adrenergic receptor produce sedation, increase focus, provide analgesia, and induce centrally mediated hypotension and bradycardia, yet neither their dynamic interactions with adrenergic receptors nor their modulation of neuronal circuit activity is completely understood. Photoaffinity ligands of α2 adrenergic agonists have the potential both to capture discrete moments of ligand–receptor interactions and to prolong naturalistic drug effects in discrete regions of tissue in vivo. We present here the synthesis and characterization of a novel α2 adrenergic agonist photolabel based on the imidazole medetomidine called azi-medetomidine. Azi-medetomidine shares protein association characteristics with its parent compound in experimental model systems and by molecular dynamics simulation of interactions with the α2A adrenergic receptor. Azi-medetomidine acts as an agonist at α2A adrenergic receptors, and produces hypnosis in Xenopus laevis tadpoles. Azi-medetomidine competes with the α2 agonist clonidine at α2A adrenergic receptors, which is potentiated by photolabeling, and azi-medetomidine labels moieties on the α2A adrenergic receptor as determined by mass spectrometry in a manner consistent with a simulated model. This novel α2 adrenergic agonist photolabel can serve as a powerful tool for in vitro and in vivo investigations of adrenergic signaling.

Ketamine Metabolite (2R,6R)-Hydroxynorketamine Interacts with μ and κ Opioid Receptors

“…Some of us have predicted a similar situation with another small ligands in another class A GPCR, the α-2A adrenergic receptor. 25 We concluded that ketamine might act as a neutral antagonist with respect to G-protein recruitment activity in both MOR and KOR; this activity is physiologically unimportant, or the experiment is confounded by the above factors.…”

Ligand- and Structure-Based Analysis of Deep Learning-Generated Potential α2a Adrenoceptor Agonists

“…While homology models have proved useful in GPCR de novo drug design, the lack of sequence similarity in the transmembrane domain regions of GPCRs has limited their accuracy . In fact, results from homology model-based α 2A -AR docking studies have recently been demonstrated to be unreliable . For the present work, molecular docking screens were run using the X-ray diffraction-resolved (3.20 Å) human α 2A -AR structure 6KUY in complex with the partial agonist (2∼{S}′)-4-fluoranyl-2-(1∼{H}-imidazole-5-yl)-1-propan-2-yl-2,3-dihydroindole (Figure ).…”

“…8 In fact, results from homology modelbased α 2A -AR docking studies have recently been demonstrated to be unreliable. 80 For the present work, molecular docking screens were run using the X-ray diffraction-resolved (3.20 Å) human α 2A -AR structure 6KUY in complex with the partial agonist (2∼{S}′)-4-fluoranyl-2-(1∼{H}-imidazole-5-yl)-1propan-2-yl-2,3-dihydroindole (Figure 4).…”

In VivoPhotoadduction of Anesthetic Ligands in Mouse Brain Markedly Extends Sedation and Hypnosis

“…Animals that failed to right themselves within 5 s of being placed supine were considered to have lost their righting reflex. Population dose–response curves for propofol and aziPm were generated using MATLAB by fitting a Hill equation and minimizing the sum of squared error between the dose–response estimate and observed data ( McKinstry-Wu et al, 2019 ).…”

“…While photo-activated chemotherapies have primarily been deployed in vitro to date, photo-activated opioids have been used in in vivo models to produce local analgesia while avoiding undesirable systemic effects ( López-Cano et al, 2021 ). Conversely, photoaffinity ligand derivatives of general anesthetics, antipsychotics, and antidepressants have been used successfully in vitro to investigate drug–receptor interactions ( Savechenkov et al, 2012 , 2017 ; Stein et al, 2012 ; Budelier et al, 2017 ; Chen et al, 2019 ; Sugasawa et al, 2019 , 2020 ), but have not been deployed in vivo in mammals to extend or enhance drug effects while limiting off-target effects ( Zawarynski et al, 1998 ; Chiara et al, 2003 ; Henry et al, 2006 ; G. D. Li et al, 2006 ; Sanghvi et al, 2008 ; McKinstry-Wu et al, 2019 ).…”