Design, Virtual Screening, and Synthesis of Antagonists of α<sub>IIb</sub>β<sub>3</sub> as Antiplatelet Agents

This article describes design, virtual screening, synthesis, and biological tests of novel α<sub>IIb</sub>β<sub>3</sub> antagonists, which inhibit platelet aggregation. Two types of α<sub>IIb</sub>β<sub>3</sub> antagonists were developed: those binding either closed or open form of the protein. At the first step, available experimental data were used to build QSAR models and ligand- and structure-based pharmacophore models and to select the most appropriate tool for ligand-to-protein docking. Virtual screening of publicly available databases (BioinfoDB, ZINC, Enamine data sets) with developed models resulted in no hits. Therefore, small focused libraries for two types of ligands were prepared on the basis of pharmacophore models. Their screening resulted in four potential ligands for open form of α<sub>IIb</sub>β<sub>3</sub> and four ligands for its closed form followed by their synthesis and <i>in vitro</i> tests. Experimental measurements of affinity for α<sub>IIb</sub>β<sub>3</sub> and ability to inhibit ADP-induced platelet aggregation (IC<sub>50</sub>) showed that two designed ligands for the open form <b>4c</b> and <b>4d</b> (IC<sub>50</sub> = 6.2 nM and 25 nM, respectively) and one for the closed form <b>12b</b> (IC<sub>50</sub> = 11 nM) were more potent than commercial antithrombotic Tirofiban (IC<sub>50</sub> = 32 nM).