The Conformational Properties of the Highly Selective Cannabinoid Receptor Ligand CP-55,940

During a search for novel drugs possessing analgesic properties but devoid of the psychotropic effects of marijuana, a group of molecules designated as nonclassical cannabinoids was synthesized by Pfizer. Of these nonclassical cannabinoids CP-55,940 has received the most attention principally because it was used as the high affinity radioligand during the discovery and characterization of the G-protein-coupled cannabinoid receptor. In an effort to obtain information on the stereoelectronic requirements at the cannabinoid receptor active site, we have studied the conformational properties of CP-55,940 using a combination of solution NMR and computer modeling methods. Our data show that for the most energetically favored conformation, (i) the aromatic phenol ring is perpendicular to the cyclohexane ring, and the phenolic O-H bond is coplanar with the aromatic ring and points away from the cyclohexyl ring; ii) the dimethylheptyl chain adopts one of four preferred conformations in all of which the chain is almost perpendicular to the phenol ring; and iii) an intramolecular H-bond between the phenolic and hydroxypropyl groups allows all three hydroxyl groups of CP-55,940 to be oriented toward the upper face of the molecule. Such an orientation by the OH groups may be a characteristic requirement for cannabimimetic activity.