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.

Synthesis of oxidative metabolites of CRA13 and their analogs: Identification of CRA13 active metabolites and analogs thereof with selective CB2R affinity.

CRA13; a peripheral dual CB1R/CB2R agonist with clinically proven analgesic properties, infiltrates into CNS producing adverse effects due to central CB1R agonism. Such adverse effects might be circumvented by less lipophilic compounds with attenuated CB1R affinity. Metabolism produces less lipophilic metabolites that might be active metabolites. Some CRA13 oxidative metabolites and their analogues were synthesized as less lipophilic CRA13 analogues. Probing their CB1R and CB2R activity revealed the alcohol metabolite 8c as a more potent and more effective CB2R ligand with attenuated CB1R affinity relative to CRA13. Also, the alcohol analogue 8b and methyl ester 12a possessed enhanced CB2R affinity and reduced CB1R affinity. The CB2R binding affinity of alcohol analogue 8b was similar to CRA13 while that of methyl ester 12a was more potent. In silico study provided insights into the possible molecular interactions that might explain the difference in the elicited biological activity of these compounds.