• Silvia Paoletta, Dilip K Tosh, Amanda Finley, Elizabeth T Gizewski, Steven M Moss, Zhan-Guo Gao, John A Auchampach, Daniela Salvemini, and Kenneth A Jacobson.
• Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, Maryland 20892-0810, United States.
• J. Med. Chem. 2013 Jul 25; 56 (14): 5949-63.

Abstract(N)-Methanocarba(bicyclo[3.1.0]hexane)adenosine derivatives were probed for sites of charged sulfonate substitution, which precludes diffusion across biological membranes, e.g., blood-brain barrier. Molecular modeling predicted that sulfonate groups on C2-phenylethynyl substituents would provide high affinity at both mouse (m) and human (h) A3 adenosine receptors (ARs), while a N(6)-p-sulfophenylethyl substituent would determine higher hA3AR vs mA3AR affinity. These modeling predictions, based on steric fitting of the binding cavity and crucial interactions with key residues, were confirmed by binding/efficacy studies of synthesized sulfonates. N(6)-3-Chlorobenzyl-2-(3-sulfophenylethynyl) derivative 7 (MRS5841) bound selectively to h/m A3ARs (Ki(hA3AR) = 1.9 nM) as agonist, while corresponding p-sulfo isomer 6 (MRS5701) displayed mixed A1/A3AR agonism. Both nucleosides administered ip reduced mouse chronic neuropathic pain that was ascribed to either A3AR or A1/A3AR using A3AR genetic deletion. Thus, rational design methods based on A3AR homology models successfully predicted sites for sulfonate incorporation, for delineating adenosine's CNS vs peripheral actions.

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