title: Synthesis of covalent probes for the radiolabeling of the cannabinoid receptor.
abstract: The main psychoactive constituent of marijuana, (-)-Delta(9)-tetrahydrocannabinol, produces most of its physiological effects by interacting with the CB1 cannabinoid receptor, a membrane protein belonging to the large superfamily of G-protein coupled receptors. The 3-D structure of the receptor binding site is of value in the design of novel medications for a variety of therapeutic indications. To obtain information on the amino acid residues associated with this binding site, we have designed and synthesized a cannabinergic CB1 ligand prototype carrying an electrophilic isothiocyanato group capable of reacting covalently with amino acid residues bearing thiol or unprotonated amino groups. The ligand also incorporates an iodide atom, which can serve as a high-activity radiolabel. The key step in our synthesis involves a rapid intramolecular Diels-Alder reaction of a transiently formed o-quinone methide, which proceeds stereospecifically with the formation of the tricyclic cannabinoid template. Introduction of the iodo group is the last step in the sequence and is compatible with the use of (125)I-radiolabel.
authors.affiliation: Chemistry Department, University of Hawaii, Honolulu, Hawaii 96822, USA.
authors.forename: Chester
authors.initials: C
authors.lastname: Chu
authors.forename: Arun
authors.initials: A
authors.lastname: Ramamurthy
authors.forename: Alexandros
authors.initials: A
authors.lastname: Makriyannis
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Tius
mesh_terms: D002186:Cannabinoids / Q000138:chemical synthesis* / Q000494:pharmacology*; D020650:Combinatorial Chemistry Techniques; D003500:Cyclization; D007457:Iodine Radioisotopes / Q000737:chemistry; D007553:Isotope Labeling; D008024:Ligands; D008958:Models, Molecular; D015335:Molecular Probes; D015394:Molecular Structure; D010084:Oxidation-Reduction; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship
chemical_list: D002186:Cannabinoids; D007457:Iodine Radioisotopes; D008024:Ligands; D015335:Molecular Probes; D043882:Receptors, Cannabinoid; D011955:Receptors, Drug