Potent quinoxaline-based inhibitors of PDGF receptor tyrosine kinase activity. Part 1: SAR exploration and effective bioisosteric replacement of a phenyl substituent. - Myers MR; He W; Hanney B; Setzer N; Maguire MP; Zulli A; Bilder G; Galzcinski H; Amin D; Needle S; Spada AP (Bioorganic & medicinal chemistry letters, 2003)