Novel non-xanthine antagonist of the A_2B adenosine receptor: From HTS hit to lead structure

The A_2B adenosine receptor is a G protein-coupled receptor that belongs to the four member family of adenosine receptors: A₁, A_2A, A_2B, A₃. While adenosine-mediated A_2B receptor signaling attenuates acute inflammation, facilitates tissue adaptation to hypoxia, and induces increased ischemia tolerance under conditions of an acute insult, persistently elevated adenosine levels and A_2B receptor signaling are characteristics of a number of chronic disease states. In this report we describe the discovery of certain thienouracils (thieno[2,3-d]pyrimidine-2,4(1H,3H)-diones) as antagonists of the A_2B adenosine receptor by high-throughput screening from our corporate substance collection. The structure optimization of the initial screening hits led to BAY-545, an A_2B receptor antagonist that was suitable for in vivo testing. The structure optimization work, SAR that was derived from there, as well as the properties of BAY-545 are also described. In vivo efficacy of BAY-545 was demonstrated in two models of lung fibrosis and data is presented.