Structural modification of an EGFR inhibitor that showed weak off-target activity against RET leading to the discovery of a potent RET inhibitor

Here, we describe the structural optimization of a known EGFR inhibitor (compound 1) that showed weak off-target activity against RET. Twenty-six analogs of 1 were synthesized. SAR analysis led to the discovery of several compounds that showed considerable potency against the RET-dependent thyroid cancer cell line TT. Kinase inhibitory potency was then measured for the most active compound (2u) in the cellular assay. The results showed that 2u is a potent RET inhibitor with an value of 7 nM.