 This was a key step in the progress of c-Met inhibitor development in that the acyl binding gives the terminal aryl group the ability to penetrate a deep hydrophobic pocket and so it enhances the potency of the compounds.Alternatives to the acyl thiourea linkage have been found, which have a pyrimidone group, as in AM7.AM7 and SU11274 offered the first proof that relatively selective c-Met inhibitors could be identified and that the inhibition leads to an anti-tumour effect in vivo.