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Discovery of Macrocyclic Pyrimidines as MerTK‐Specific Inhibitors

Macrocycles have attracted significant attention in drug discovery recently. In fact, a few de novo designed macrocyclic kinase inhibitors are currently in clinical trials with good potency and selectivity for their intended target. In this study, we successfully engaged a structure‐based drug design approach to discover macrocyclic pyrimidines as potent Mer tyrosine kinase (MerTK)‐specific inhibitors. An enzyme‐linked immunosorbent assay (ELISA) in 384‐well format was employed to evaluate the inhibitory activity of macrocycles in a cell‐based assay assessing tyrosine phosphorylation of MerTK. Through structure–activity relationship (SAR) studies, analogue 11 [UNC2541; (S)‐7‐amino‐N‐(4‐fluorobenzyl)‐8‐oxo‐2,9,16‐triaza‐1(2,4)‐pyrimidinacyclohexadecaphane‐1‐carboxamide] was identified as a potent and MerTK‐specific inhibitor that exhibits sub‐micromolar inhibitory activity in the cell‐based ELISA. In addition, an X‐ray structure of MerTK protein in complex with 11 was resolved to show that these macrocycles bind in the MerTK ATP pocket.