Discovery and optimization of 4-(imidazo[1,2-a]pyrimidin-3-yl)thiazol-2-amine derivatives as novel phosphodiesterase 4 inhibitors.

Phosphodiesterases (PDEs) are important intracellular enzymes that hydrolyze the second messengers cAMP and/or cGMP. Now several studies have shown that PDE4 received particular attention due to which it represents the most prominent cAMP-metabolizing enzyme involved in many diseases. In this study, we performed prescreening of our internal compound library and discovered the compound (PTC-209) with moderate PDE4 inhibitory activity (IC₅₀ of 4.78 ± 0.08 μM). And a series of 4-(imidazo[1,2-a]pyrimidin-3-yl)thiazol-2-amine derivatives as novel PDE4 inhibitors starting from PTC-209 were successfully designed and synthesized using a structure-based discovery strategy. L19, the most potent inhibitor, exhibited good inhibitory activity (IC₅₀ of 0.48 ± 0.02 μM) and remarkable metabolic stability in rat liver microsomes. Our study presents an example of discovery novel PDE4 inhibitors, which would be helpful for design and optimization of novel inhibitors in future.