N6-substituted-5'-C-ethyi-tetrazolyl-adenosine derivatives: potent dual acting A1 and A3 adenosine receptor iigands with analgesic properties

Adenosine (Ado) is the endogenous ligand of a family of G-protein coupied receptors (GPCRs) represented by four subtypes: Ai, A2A, A2B, and A3 adenosine receptors (ARs). They are widely distributed in all the human body including the central nervous system (CNS), peripheral neurons, cardiovascular system, respiratory tract and immune system [1]. Affinity and selectivity towards the four ARs can be modulated through substitutions at both purine and sugar moiety of adenosine. The replacement of the 5'-hydroxyl group with a chlorine atom in /V6-substituted adenosine derivatives led to discovery of 5'-chloro-5'-deoxy-/V6-(±)-(endo-norborn-2-yl)- adenosine (5'CI5'd-(±)-ENBA), a potent and selective A1AR agonist that showed analgesic effects in mice without affecting cardiovascular and motor functìons [2]. Introduction of a 5'-C-ethyltetrazol-2-yl group, together with the appropriate N6-substitution in adenosine derivatives, furnished compounds endowed with an increased affinity versus both hA1AR and hA3AR, reaching affinities in subnanomolar range [3]. In this work, a new series of 5'-C-ethyltetrazol-2-yl-N6-substituted adenosine derivatives were designed, synthesized and tested in vitro in binding and functional assays and in vivo in a mouse model of pain. The molecular features necessary for the hA1- and hA3AR recognition and activation by this series of derivatives were explained through an in silice receptor-driven approach. [1] K. A. Jacobson and C. E. Muller, Neuropharmacology 104(2016) 31-49. [2] L. Luongo, R. Petrelli, L. Gatta, C. Giordano, F. Guida, P. Vita, P. Franchetti, M. Grifantini, V. De Novellls, L. Cappellacci, and S. Maione, Molecules 17 (2012) 13712-13726. [3] R. Petrelli, I. Torquati, S. Kachler, L. Luongo, S. Maione, P. Franchetti, M. Grifantini, E. Novellino, A. Lavecchia, K.-N. Klotz, and L. Cappellacci, J. Med. Chem. 58 (2015) 2560-2566.