Conformationally Constrained Fatty Acid Ethanolamides as Cannabinoid and Vanilloid Receptor Probes

To investigate if certain acylethanolamides bind to both cannabinoid (CB1 and CB2) and vanilloid TRPV1 receptors because of their conformational flexibility, we introduced a methylene lock on their ethanolamine "head", thereby generating a cyclopropane ring with two stereogenic centers and chiral cis/trans diastereomers with different topology of presentation to binding sites. After resolution by chiral-phase HPLC, diastereo-and enantiopure arachidonoyl-, oleoyl-, and palmitoylcyclopropanolamides were tested in assays of CB1, CB2, and TRPV1 activity. Diastereodifferentiation between pairs of cis-trans isomers was observed only for TRPV1 activity, with poor enantiodifferentiation. Methylenation introduced (i) CB1 receptor affinity in oleoylethanolamide while increasing in a diastereoselective way its activity at TRPV1 and (ii) strong diastereoselective activity at TRPV1, but not cannabinoid, receptors in the otherwise inactive palmitoylethanolamide. These results show that the N-alkyl group of acylethanolamides has a different role in their interaction with cannabinoid and vanilloid receptors and that acylcyclopropanolamides qualify as CB1/TRPV1 "hybrids" of potential therapeutic utility.