Selective, direct activation of high-conductance, calcium-activated potassium channels causes smooth muscle relaxation.

High-conductance calcium-activated potassium (Maxi-K) channels are present in smooth muscle where they regulate tone. Activation of Maxi-K channels causes smooth muscle hyperpolarization and shortening of action-potential duration, which would limit calcium entry through voltage-dependent calcium channels leading to relaxation. Although Maxi-K channels appear to indirectly mediate the relaxant effects of a number of agents, activators that bind directly to the channel with appropriate potency and pharmacological properties useful for proof-of-concept studies are not available. Most agents identified to date display significant polypharmacy that severely compromises interpretation of experimental data. In the present study, a high-throughput, functional, cell-based assay for identifying Maxi-K channel agonists was established and used to screen a large sample collection (>1.6 million compounds). On the basis of potency and selectivity, a family of tetrahydroquinolines was further characterized. Medicinal chemistry efforts afforded identification of compound X, from which its two enantiomers, Y and Z, were resolved. In in vitro assays, Z is more potent than Y as a channel activator. The same profile is observed in tissues where the ability of either agent to relax precontracted smooth muscles, via a potassium channel-dependent mechanism, is demonstrated. These data, taken together, suggest that direct activation of Maxi-K channels represents a mechanism to be explored for the potential treatment of a number of diseases associated with smooth muscle hyperexcitability.

Synthesis and biological activity of pyridopyridazin-6-one p38α MAP kinase inhibitors. Part 2.

This manuscript concludes the Structure Activity Relationship (SAR) on the pyridazinone scaffold and identifies a compound with subnanomolar p38α activity and 24h coverage in the rat arthritis efficacy model.

Synthesis and biological activity of pyridopyridazin-6-one p38 MAP kinase inhibitors. Part 1.

The development and synthesis of potent p38α MAP kinase inhibitors containing a pyridazinone platform is described. Evolution of the p38α selective pyridopyridazin-6-one series from the p38α/ß dual inhibitor 2H-quinolizin-2-one series will be discussed in full detail.

Synthesis and biological activity of 2H-quinolizin-2-one based p38alpha MAP kinase inhibitors.

The development and synthesis of potent p38alpha MAP kinase inhibitors containing a 2H-quinolizin-2-one platform is described. Evolution of the 2H-quinolizin-2-one series from an early lead to solving off target activity and pharmacokinetic issues is also discussed.

Synthesis and biological activity of quinolinone and dihydroquinolinone p38 MAP kinase inhibitors.

Synthesis and biological activities of some quinolinone and dihydroquinolinone p38 MAP kinase inhibitors are reported. Modifications to the dihydroquinolinone pharmacophore revealed that dihydroquinolinone may be replaced with a quinolinone pharmacophore and lead to enhanced p38 inhibitory activity. From a study of C-7 substitutions by amino acid side chains, a very potent series of compounds in the p38 enzyme assays was identified. Translation of the in vitro activity into reasonable whole blood activity can be improved in this series of compounds by judicious modification of the physical properties at appropriate regions of the lead.

P38 MAP kinase inhibitors: evolution of imidazole-based and pyrido-pyrimidin-2-one lead classes.

The initial disclosure of tri-substituted imidazole-based drug molecules such as 1 for inhibition of p38 MAP kinase by SmithKline Beecham (SB) sparked an effort in this area at Merck and other pharmaceutical research establishments. Although analogs in this class have shown good inhibitory properties against p38 MAP kinase, their selectivity profile were modest and left much room for improvement. Attempts to discover newer compounds with improved selectivity over the prototypical SB compound 203580 (1), led to the discovery of a new sub-class of p38 inhibitors typified by compound 18 at Merck. Although this benchmark compound was potent, highly selective and orally efficacious it was burdened with compound related adverse effects in dogs that has delayed further development. In 1999, a new class of p38 inhibitors represented by clinical candidate VX-745 (26), was disclosed by Vertex Pharmaceuticals. This compound displayed unprecedented selectivity due to its unique mode of binding to the active site in p38 MAP kinase. Inspired by the exquisite selectivity profile of VX-745 [26] a scaffold re-design was initiated at Merck which resulted in the discovery of the quinazolinone, pyrimido-pyrimidone, pyrido-pyrimidone, quinolinone and naphthyridinone based p38 inhibitors.

Hybrid-designed inhibitors of p38 MAP kinase utilizing N-arylpyridazinones.

Imidazo[1,2-a]pyridyl N-arylpyridazinones were hybridized from the classic pyridinylimidazoles and the more recent dual hydrogen bond acceptors, resulting in a new structural class of selective p38 MAP kinase inhibitors.

p38 MAP kinase inhibitors: metabolically stabilized piperidine-substituted quinolinones and naphthyridinones.

Quinolinones and naphthyridinones with C7 N-t-butyl piperidine substituents were found to be potent p38 MAP kinase inhibitors. These compounds significantly suppress TNF-alpha release in both cellular and LPS-stimulated whole blood assays. They also displayed excellent PK profiles across three animal species. Quinolinone at 10 mpk showed comparable oral efficacy to that of dexamethasone at 1 mpk in a murine collagen-induced arthritis model.

SAR of 3,4-dihydropyrido[3,2-d]pyrimidone p38 inhibitors.

Development for a class of potent 3,4-dihydropyrido(3,2-d)pyrimidone inhibitors of p38a MAP kinase is described. Modification of N-1 aryl and C-6 arylsulfide in 3,4-dihydropyrido(3,2-d)pyrimidone analogues for the interaction with the hydrophobic pockets in p38 active site is also discussed.

p38 Inhibitors: piperidine- and 4-aminopiperidine-substituted naphthyridinones, quinolinones, and dihydroquinazolinones.

We have synthesized a series of C7-piperidine- and 4-aminopiperidine-substituted naphthyridinones, quinolinones, and dihydroquinazolinones that are highly potent inhibitors of both p38MAP kinase activity and TNF-alpha release. The 4-aminopentamethylpiperidine naphthyridinone 5, which was designed to block metabolism at major 'hot spots', combined excellent inhibitory potency with good oral bioavailability in the rat.

p38MAP kinase inhibitors. Part 1: design and development of a new class of potent and highly selective inhibitors based on 3,4-dihydropyrido[3,2-d]pyrimidone scaffold.

A new class of p38 antagonists based on 3,4-dihydropyrido[3,2,-d]pyrimidine scaffold has been developed. These inhibitors exhibit unprecedented selectivity towards p38 over other very closely related kinases. Compounds 25, 33, and 34 were identified as benchmark analogues for follow-up studies. They show good potency for enzyme inhibition and excellent functional activity.

Design and synthesis of potent, orally bioavailable dihydroquinazolinone inhibitors of p38 MAP kinase.

The development of potent, orally bioavailable (in rat) and selective dihydroquinazolinone inhibitors of p38alpha MAP kinase is described. These analogues are hybrids of a pyridinylimidazole p38alpha inhibitor reported by Merck Research Laboratories and VX-745. Optimization of the C-5 phenyl and the C-7 piperidinyl substituents led to the identification of 15i which gave excellent suppression of TNF-alpha production in LPS-stimulated whole blood (IC(50)=10nM) and good oral exposure in rats (F=68%, AUCn PO=0.58 microM h).