Highly Selective, Amine‐Derived Cannabinoid Receptor 2 Probes

Abstract

The endocannabinoid (eCB) system is implied in various human diseases ranging from central nervous system to autoimmune disorders. Cannabinoid receptor 2 (CB2R) is an integral component of the eCB system. Yet, the downstream effects elicited by this G protein‐coupled receptor upon binding of endogenous or synthetic ligands are insufficiently understood—likely due to the limited arsenal of reliable biological and chemical tools. Herein, we report the design and synthesis of CB2R‐selective cannabinoids along with their in vitro pharmacological characterization (binding and functional studies). They combine structural features of HU‐308 and AM841 to give chimeric ligands that emerge as potent CB2R agonists with high selectivity over the closely related cannabinoid receptor 1 (CB1R). The synthesis work includes convenient preparation of substituted resorcinols often found in cannabinoids. The utility of the synthetic cannabinoids in this study is showcased by preparation of the most selective high‐affinity fluorescent probe for CB2R to date.

Development of High-Specificity Fluorescent Probes to Enable Cannabinoid Type 2 Receptor Studies in Living Cells

“…In addition, the model predicts a hydrogen-bond between the amide-proton of 3b and the carbonyl oxygen of Ser90, which contributes to the high affinity of the probe. 39 When the docking pose of 3b was compared with the recently published co-crystal structure of active state CB2R in complex with agonist WIN55,212-2 48 the binding mode of the docked core motif was found to be identical, and the hydrogen bond with Ser90 was maintained.…”

“…With a high-affinity recognition element, such as 1, 39 as a starting point, choice of the exit vector and linker-type for fluorophore attachment are the main challenges to ensure high probe affinity and selectivity. 40,41 Our preliminary synthetic studies with 2 suggested a strategy for a family of fluorescent probes.…”

Optical Control of Cannabinoid Receptor 2-Mediated Ca2+ Release Enabled by Synthesis of Photoswitchable Probes

“…In this regard, replacement of the allylic alcohol in HU308 with an amide linkage enabled attachment of fluorescent dyes and led to highly specific probes. 31,32, A wide range of substituents are tolerated at this position without affecting affinity as they extend out of the orthosteric binding pocket of CB2. By contrast, optical control over receptor activity requires identification of a different locus for photoswitch conjugation.…”

“…1). 31,32 Azobenzenes are the presently preferred switch in photopharmacology. 33 We devised three photoswitchable HU308 derivatives harboring azobenzenes.…”

The Role of Cannabinoids in Allergic Diseases: Collegium Internationale Allergologicum (CIA) Update 2020

“…Their ability to bind different streptavidin tags made them suitable to study and visualize CBRs in native systems [170]. Moreover, several CB2-specific probes based on photoaffinity and fluorescent labelling have also been developed [171][172][173][174][175]. Their capacity to track CB2 in various cell types and settings may be of quite some interest in studies monitoring the expression of CB2 and its interactions in biological systems (Table 2).…”