Identification of the fused bicyclic 4-amino-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors

2-Phenyl-4-piperidinyl-6,7-dihydrothieno[3,4-d] pyrimidine derivative (2) was found to be a new PDE4 inhibitor with moderate PDE4B activity (IC50 = 150 nM). A number of derivatives with a variety of 4-amino substituents and fused bicyclic pyrimidines were synthesized. Among these, 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d] pyrimidine derivative (18) showed potent PDE4B inhibitory activity (IC50 = 25 nM). Finally, N-propylacetamide derivative (31b) was determined as a potent inhibitor for both PDE4B (IC50 = 7.5 nM) and TNF-alpha production in mouse splenocytes (IC50 = 9.8 nM) and showed good in vivo anti-inflammatory activity in the LPS-induced lung inflammation model in mice (ID50 = 18 mg/kg). The binding mode of the new inhibitor (31e) in the catalytic site of PDE4B is presented based on an X-ray crystal structure of the ligand-enzyme complex. (C) 2013 Elsevier Ltd. All rights reserved.