Tyrphostins. 5. Potent inhibitors of platelet-derived growth factor receptor tyrosine kinase: Structure-activity relationships in quinoxalines, quinolines, and indole tyrphostins

A series of 3-indoleacrylonitrile tyrphostins, 2-chloro-3- phenylquinolines, and 3-arylquinoxalines were prepared and tested for inhibition of platelet-derived growth factor receptor tyrosine kinase (PDGF- RTK) activity. The potency of the inhibitors was found to be quinoxalines > quinolines > indoles. Lipophilic groups (methyl, methoxy) in the 6 and 7 positions and phenyl at the 3 position of quinoxalines and quinolines were essential for potency, in contrast to the hydrophilic catechol group in tyrphostins active against EGFR kinase inhibition at different sites. The inhibitors showed selectivity for PDGF and were not active against EGF receptor and HER-2/c-ErbB-2 receptor.