4’-TETRAZOLYL-ALKYL-N6-SUBSTITUTED ADENOSINE DERIVATIVES AS HIGHLY POTENT DUAL ACTING A1 ADENOSINE RECEPTOR AGONISTS AND A3 ADENOSINE RECEPTOR ANTAGONISTS

Adenosine is an endogenous purine nucleoside that modulates a variety of physiological functions as a result of its activation of specific G protein-coupled receptors defined as A1, A2A, A2B, and A3 adenosine receptors (ARs). Selective A1AR agonists mediate neuro- and cardioprotective effects, and reduce lipolysis in adipose tissue and elevated intraocular pressure (IOP), the most widely recognized risk factor for the onset and progression of glaucoma. Selective A3AR agonists have been demonstrated to be both cardio- and cerebroprotective. Moreover, it has been reported that A3 agonists increase, whereas A3 antagonists decrease IOP in mice. A selective A3 antagonist, OT-7999 is being studied for the treatment of glaucoma, whereas an A1 agonist, INO-8875/PJ-875, is in Phase I/II for the treatment of patients with ocular hypertension or primary open angle glaucoma (POAG). Recent findings indicated that some compounds might activate two different subtypes of a certain receptor family, both leading to beneficial effects. The dual-acting ligands of ARs may have considerable promise as novel approaches to treat pathological conditions e.g. ischemic conditions, asthma, inflammatory diseases and glaucoma. In our previous work we reported that N6-substitution in 5’-chloro-5’-deoxy-adenosine derivatives with cycloalkyl- or bicycloalkyl groups led to very potent and selective A1 agonists.1 5’Cl5'd-(±)-ENBA was the most potent and selective A1 agonist of the series and was endowed with analgesic activity in SNI mice,2,3 a model of neuropathic pain. Functional assays showed that 5’Cl5'd-(±)-ENBA was a full A1 agonist and a weak A3 antagonist, confirming that the lack of a group hydrogen bonding donor in the A3AR binding site alters the ability to induce the conformational change essential for receptor activation. As the proof of the concept and in order to find dual acting A1AR agonists and A3AR antagonists, we designed and synthesized a new series of N6-substituted adenosine and 2-chloro-adenosine derivatives in which the 4’-hydroxymethyl group was replaced by a 2-ethyl-2H-tetrazol-5-yl moiety. The novel compounds displayed a subnanomolar affinity at both A1 and A3ARs and acted as A1 full agonists and A3 antagonists. These compounds represent the first example of highly potent dual acting A1AR agonists and A3AR antagonists useful for the treatment of glaucoma and other diseases. References: (1) P Franchetti, L Cappellacci et al. J. Med. Chem. 2009, 52, 2393-2406. (2) L Luongo, L Cappellacci, et al. Molecules, 2012, 17, 13712-13726. (3) L Luongo, L Cappellacci et al. Glia, 2014, 62, 122-132.