Identification of the 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives as highly selective PDE4B inhibitors.

A PDE4B subtype selective inhibitor is expected to have a wider therapeutic window than non-selective PDE4 inhibitors. In this Letter, two series of 7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives and 5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivatives were evaluated for their PDE4B subtype selectivity using human PDE4B2 and PDE4D2 full length enzymes. To improve their PDE4B selectivity over PDE4D, we optimized the substituents on the pyrimidine ring and the side chain phenyl ring, resulting in several derivatives with more than 100-fold selectivity for PDE4B. Consequently, we identified 2-(3-chloro-4-methoxy-phenyl)-5,5-dioxo-7,8-dihydro-6H-thiopyrano[3,2-d]pyrimidine derivative 54 as a highly selective PDE4B inhibitor, which had potent hPDE4B inhibitory activity with an IC50 value of 3.0 nM and 433-fold PDE4B selectivity over PDE4D.

Evaluation of the therapeutic index of a novel phosphodiesterase 4B-selective inhibitor over phosphodiesterase 4D in mice.

Phosphodiesterase 4 (PDE4) inhibitors have been developed for the treatment of pulmonary inflammatory diseases, but their clinical use was dose-limited by mainly gastric adverse effects. Recent studies suggested PDE4B-selective inhibitors over PDE4D are supposed to display a wider therapeutic index than subtype non-selective PDE4 inhibitors such as roflumilast. Compound A was identified as an orally active PDE4B-selective inhibitor over PDE4D both in humans (80-fold selective) and mice (29-fold selective). In this study, the therapeutic effects of compound A and roflumilast were evaluated on lipopolysaccaride (LPS) injection-induced plasma TNF-α elevation and on LPS inhalation-induced pulmonary neutrophilia in mice. The inhibitory effect on gastric emptying in mice was evaluated as a gastric adverse effect. The therapeutic index for TNF-α production (TI(TNF) = ID50 in gastric emptying / ID50 in LPS injection-induced plasma TNF-α elevation) of compound A was larger than roflumilast (9.0 and 0.2, respectively), whereas the therapeutic index for pulmonary neutrophilia (TI(Neu) = ID50 in gastric emptying / ID50 in LPS inhalation-induced pulmonary neutrophilia) of compound A was comparable to roflumilast (1.0 and 0.5, respectively). In conclusion, the TI(Neu) of compound A was not superior compared to that of roflumilast in spite of its high selectivity for PDE4B over PDE4D in mice.

Synthesis and biological evaluation of 5-carbamoyl-2-phenylpyrimidine derivatives as novel and potent PDE4 inhibitors.

5-Carbamoyl-2-phenylpyrimidine derivative 2 has been identified as a phosphodiesterase 4 (PDE4) inhibitor with moderate PDE4B inhibitory activity (IC50=200 nM). Modification of the carboxylic acid moiety of 2 gave N-neopentylacetamide derivative 10f, which had high in vitro PDE4B inhibitory activity (IC50=8.3 nM) and in vivo efficacy against lipopolysaccharide (LPS)-induced pulmonary neutrophilia in mice (ID50=16 mg/kg, ip). Furthermore, based on the X-ray crystallography of 10f bound to the human PDE4B catalytic domain, we designed 7,8-dihydro-6H-pyrido[4,3-d]pyrimidin-5-one derivative 39 which has a fused bicyclic lactam scaffold. Compound 39 exhibited excellent inhibitory activity against LPS-induced tumor necrosis factor alpha (TNF-α) production in mouse splenocytes (IC50=0.21 nM) and in vivo anti-inflammatory activity against LPS-induced pulmonary neutrophilia in mice (41% inhibition at a dose of 1.0 mg/kg, i.t.).

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-α 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.

Tuning sensitivity to IL-4 and IL-13: differential expression of IL-4Ralpha, IL-13Ralpha1, and gammac regulates relative cytokine sensitivity.

Interleukin (IL)-4 and -13 are related cytokines sharing functional receptors. IL-4 signals through the type I (IL-4Ralpha/common gamma-chain [gammac]) and the type II (IL-4Ralpha/-13Ralpha1) IL-4 receptors, whereas IL-13 utilizes only the type II receptor. In this study, we show that mouse bone marrow-derived macrophages and human and mouse monocytes showed a much greater sensitivity to IL-4 than to IL-13. Lack of functional gammac made these cells poorly responsive to IL-4, while retaining full responsiveness to IL-13. In mouse peritoneal macrophages, IL-4 potency exceeds that of IL-13, but lack of gammac had only a modest effect on IL-4 signaling. In contrast, IL-13 stimulated greater responses than IL-4 in fibroblasts. Using levels of receptor chain expression and known binding affinities, we modeled the assemblage of functional type I and II receptor complexes. The differential expression of IL-4Ralpha, IL-13Ralpha1, and gammac accounted for the distinct IL-4-IL-13 sensitivities of the various cell types. These findings provide an explanation for IL-13's principal function as an "effector" cytokine and IL-4's principal role as an "immunoregulatory" cytokine.