SYNTHESIS OF ISOTOPE-LABELED CB LIGANDS FOR NMR STUDIES

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DESCRIPTION (Applicant's Abstract): Since the two cannabinoid receptor subtypes (CB1, CB2) have been identified as a subgroup of the Gi protein-coupled seven-transmembrane-spanning receptor superfamily, a great effort has been directed toward understanding the molecular-level interactions between the CB receptor and its ligand, as well as designing novel cannabimimetic ligands possessing therapeutically useful biological properties but devoid of the psychotropic effects of marijuana. However, many unanswered questions about the molecular-level interactions between the receptor and the cannabimimetic ligands, the nature of the receptor active site(s), and their three-dimensional structures remain to be addressed. The objective of this research proposal is to obtain information on the molecular properties of cannabimimetic agents in membranes (in order to mimic the receptor environment) through the combined use of nuclear magnetic resonance (NMR) and computer modeling methods. Such information is of critical importance for the design of novel analogs of potential therapeutic value. The conformational properties of a judiciously chosen group of analogs related to three known cannabimimetic groups, namely arachidonylethanolamides (AEAs), aminoalkylindoles (AAIs), and pyrazoles (PRZs) will be studied using NMR methods and then refined using computer modeling approaches. 1) A special effort will be made to study the conformations of these molecules in a membrane environment. The 3D structure of the ligand in the membrane will be obtained using a variety of NMR techniques including multidimensional NMR experiments with pulse gradients, Transfer NOE and Rotational Echo Double Resonance experiments. 2) Computer modeling will be used to refine the NMR-determined conformations. Comparative Molecular Field Analysis (CoMFA) and the Active Analog Approach will be applied to examine the definition of pharmacophores and to define the active site as well as to map receptor volume. The pharmacophoric model defined by NMR experiments and theoretical calculations can be used as a guide for designing novel CB ligands and predicting the biological behavior of other untested compounds. The procedures developed will eventually be used to directly study the conformation of receptor-bound ligands in the future. Overall, the studies will provide insights into the design of a new generation of ligands possessing enhanced biological activity.