Fluorinated CRA13 analogues: Synthesis, in vitro evaluation, radiosynthesis, in silico and in vivo PET study.

Fluorine is a unique atom that imparts distinct properties to bioactive molecules upon incorporation. Herein, we prepare and study fluorinated derivatives of the nanomolar affine peripherally restricted dual CB1R/CB2R agonist; CRA13 and its analogs. Binding affinity evaluation relative to CRA13 proved the stronger binding affinity of compound 7c to CB1R and CB2R by 6.95 and 5.64 folds. Physicochemical properties evaluation proved compound 7c improved lipophilicity profile suggesting some enhanced BBB penetration relative to CRA13. Radiosynthesis of 18F-labeled compound 7c was conducted conveniently affording pure hot ligand. In vivo PET study investigation demonstrated efficient distribution of 18F-labeled compound 7c in peripheral tissues visualizing peripheral CB1R/CB2R generating time-activity-curves showing good standard uptake values. Despite enhanced BBB penetration and increased cannabinoid receptors binding affinity, low brain uptake of 7c was observed. In silico docking study explained the measured binding affinities of compounds 7a-d to CB1R. While most of previous efforts aimed to develop central cannabinoid PET imaging agents, 18F-labeled compound 7c might be a promising agent serving as a universal CB1R/CB2R PET imaging agents for diagnosis and therapy of various diseases correlated with peripheral cannabinoid system. It might also serve as a lead compound for development of PET imaging of peripheral and central cannabinoid systems.