4-anilino-3-quinolinecarbonitriles: an emerging class of kinase inhibitors

The first potent selective small molecule inhibitor of a protein kinase was reported in 1994 by Parke-Davis. PD-153035, 4-(3-bromoanilino)-6,7-dimethoxyquinazoline, is an ATP competitive inhibitor of the epidermal growth factor receptor tyrosine kinase (EGFr), with no appreciable inhibitory activity against several other kinases. Subsequent structural elaboration of PD-153035 led to several 4-anilinoquinazolines that are currently in various stages of clinical trials for the treatment of kinase-mediated diseases. A homology model of EGFr with PD-153035 suggested that the 3-nitrogen atom of the quinazoline ring binds a water molecule. It was envisioned that this nitrogen atom could be replaced by a carbon atom containing an electron-withdrawing group. This critical observation by a group at Wyeth led to the identification of 4-(3-bromoanilino)-6,7-dimethoxy-3-quinolinecarbonitrile as an EGFr inhibitor. It was subsequently established that variation of the substituents on the 4-anilino group of the 6,7-dimethoxy-3-quinolinecarbonitrile changed the kinase specificity from EGFr to other kinases including Src and MEK. The 3-quinolinecarbonitrile template was also utilized to develop an irreversible inhibitor of EGFr, EKB-569, currently in clinical trials for the treatment of cancer. Further manipulation of the 3-quinolinecarbonitrile core provided tricyclic analogs, with the most potent kinase inhibitory activity observed with a benzo[g]quinoline-3-carbonitrile ring system. It was also found that 3-quinolinecarbonitriles with a 7-thiophene or phenyl substituent were potent Src kinase inhibitors.