Structure-Activity Relationship and Functional Evaluation of Cannabinoid Type-1 Receptor.

The type-1 cannabinoid receptor (CBR) is a potential therapeutic target in several pathological conditions, including neuropsychological disorders and neurodegenerative diseases. Owing to their structural diversity, it is not easy to derive general structure-activity relationships (SARs) for CBR ligands. In this study, CBR ligands were classified into six structural families, and the corresponding SAR was determined for their affinities for CBR. In addition, we determined their functional activities for the activation of extracellular signal-regulated kinases (ERKs). Among derivatives of indol-3-yl-methanone, the highest ligand affinity was observed when a pentyl and a naphthalenyl group were attached to the N1 position of the indole ring and the carbon site of the methanone moiety, respectively. In the case of adamantane indazole-3-carboxamide derivatives, the presence of fluorine in the pentyl group, the substituent at the N1 position of the indazole ring, strongly increased the affinity for CBR. For (naphthalen-1-yl) methanone derivatives, the presence of 4-alkoxynaphthalene in the methanone moiety was more beneficial for the affinity to CBR than that of a heterocyclic ring. The functional activities of the tested compounds, evaluated through ERK assay, were correlated with their affinity for CBR, suggesting their agonistic nature. In conclusion, this study provides valuable insight for designing novel ligands for CBR, which can be used to control psychiatric disorders and drug abuse.