Efficient, large-scale synthesis and preclinical studies of MRS5698, a highly selective A3 adenosine receptor agonist that protects against chronic neuropathic pain

We reported that 2-(3,4-difluorophenylethynyl)-N-6-3-chlorobenzyl (N)-methanocarba adenosine derivative 1 (MRS5698) binds selectively to human and mouse A3 adenosine receptors (A(3)ARs, K-i 3 nM). It is becoming an important pharmacological tool for defining A(3)AR effects and is orally active in a chronic neuropathic pain model. Here, we introduce a new synthetic route for MRS5698 from D-ribose, suitable for a scale-up on a multi-gram scale, and we measure in vitro and in vivo ADME-Tox parameters. MRS5698 was very stable in vitro, failed to inhibit CYPs at <10 mu M, and was largely bound to plasma proteins. It was well tolerated in the rat at doses of <= 200 mg/kg i.p. A 1 mg/kg i.p. dose in the mouse displayed t(1/2) of 1.09 h and plasma C-max of 204 nM at 1 h with an AUC of 213 ngxh/mL. CACO-2 bidirectional transport studies suggested intestinal efflux of MRS5698 (efflux ratio 86). Although the oral % F is only 5 %, the beneficial effect to reverse pain lasted for at least 2 h in the CCI model in rats, using the same vehicle for oral administration of a high dose. The stability, low toxicity, lack of CYP interaction, pharmacokinetic half-life, and in vivo efficacy suggest that MRS5698 is a preferred compound for further consideration as a treatment for neuropathic pain.