Discovery and characterization of 6-{4-[3-(R)-2-methylpyrrolidin-1-yl)propoxy]phenyl}-2H-pyridazin-3-one (CEP-26401, irdabisant): a potent, selective histamine H3 receptor inverse agonist.

Optimization of a novel series of pyridazin-3-one histamine H(3) receptor (H(3)R) antagonists/inverse agonists identified 6-{4-[3-(R)-2-methylpyrrolidin-1-yl)propoxy]phenyl}-2H-pyridazin-3-one (8a, CEP-26401; irdabisant) as a lead candidate for potential use in the treatment of attentional and cognitive disorders. 8a had high affinity for both human (K(i) = 2.0 nM) and rat (K(i) = 7.2 nM) H(3)Rs with greater than 1000-fold selectivity over the hH(1)R, hH(2)R, and hH(4)R histamine receptor subtypes and against an in vitro panel of 418 G-protein-coupled receptors, ion channels, transporters, and enzymes. 8a demonstrated ideal pharmaceutical properties for a CNS drug in regard to water solubility, permeability and lipophilicity and had low binding to human plasma proteins. It weakly inhibited recombinant cytochrome P450 isoforms and human ether-a-go-go-related gene. 8a metabolism was minimal in rat, mouse, dog, and human liver microsomes, and it had good interspecies pharmacokinetic properties. 8a dose-dependently inhibited H(3)R agonist-induced dipsogenia in the rat (ED(50) = 0.06 mg/kg po). On the basis of its pharmacological, pharmaceutical, and safety profiles, 8a was selected for preclinical development. The clinical portions of the single and multiple ascending dose studies assessing safety and pharmacokinetics have been completed allowing for the initiation of a phase IIa for proof of concept.

Synthesis and discovery of 2,3-dihydro-3,8-diphenylbenzo[1,4]oxazines as a novel class of potent cholesteryl ester transfer protein inhibitors.

2,3-Dihydro-3,8-diphenylbenzo[1,4]oxazines were identified as a new class of potent cholesteryl ester transfer protein inhibitors. The most potent compound 6a (IC50=26 nM) possessed a favorable pharmacokinetic profile with good oral bioavailability in rat (F=53%) and long human liver microsome stability (t(1/2)=62 min). It increased HDL-C in human CETP transgenic mice and high-fat fed hamsters. The structure and activity relationship of this series will be described in this Letter.

Synthesis and structure-activity relationships of pyrazine-pyridine biheteroaryls as novel, potent, and selective vascular endothelial growth factor receptor-2 inhibitors.

There is much evidence that direct inhibition of the kinase activity of vascular endothelial growth factor receptor-2 (VEGFR-2) will result in the reduction of angiogenesis and the suppression of tumor growth. Palladium-catalyzed C-C bond, C-N bond formation reactions were used to assemble various pyrazine-pyridine biheteroaryls as potent VEGFR-2 inhibitors. Among them, 4-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-ylamino}-butan-1-ol (39) and N-{5-[6-(3-chloro-phenylamino)-pyrazin-2-yl]-pyridin-3-yl}-N',N'-dimethyl-ethane-1,2-diamine (41) exhibited the highest kinase selectivity against fibroblast growth factor receptor kinase, platelet-derived growth factor receptor kinase, and glycogen synthase kinase-3. All of these compounds showed good cellular potency to inhibit VEGF-stimulated proliferation of human umbilical vein endothelial cells (HUVEC) but with modest effects on the unstimulated growth of HUVEC. The low inhibition of these compounds to the growth of tumor cell lines, such as HeLa, HCT-116, and A375 further confirms that these VEGFR-2 inhibitors are not cytotoxic agents. The in vivo antitumor activity of 39 and 41 were demonstrated in the A375 human melanoma xenograft nude mice model. Molecular modeling (QSAR analysis) was conducted in an attempt to rationalize the observed structure-activity relationship.

Design, synthesis, and biological evaluation of novel 7-azaindolyl-heteroaryl-maleimides as potent and selective glycogen synthase kinase-3beta (GSK-3beta) inhibitors.

Two approaches were developed to synthesize the novel 7-azaindolyl-heteroarylmaleimides. The first approach was based upon the palladium-catalyzed Suzuki cross-coupling or Stille cross-coupling of 2-chloro-maleimide 5 with various arylboronic acids or arylstannanes. The second approach was based upon the condensation of ethyl 7-azaindolyl-3-glyoxylate 12 with various acetamides. The hydroxypropyl-substituted 7-azaindolylmaleimide template was first used to screen different heteroaryls attached to the maleimide. Replacement of hydroxypropyl with different chain lengths and different functional groups were studied next. Many compounds synthesized were demonstrated to have high potency at GSK-3beta, good GS activity in HEK293 cells and good to excellent metabolic stability in human liver microsomes. Three representative compounds (21, 33, and 34) were demonstrated to have good selectivity against a panel of 80 kinase assays. Among them, compound 33 exhibited very weak inhibitions at the other 79 kinase assays, and behaved as a highly selective GSK-3beta inhibitor.

Synthesis and biological evaluation of novel macrocyclic bis-7-azaindolylmaleimides as potent and highly selective glycogen synthase kinase-3 beta (GSK-3 beta) inhibitors.

Palladium catalyzed cross-coupling reactions were used to synthesize two key intermediates 3 and 5 that resulted in the synthesis of novel series of macrocyclic bis-7-azaindolylmaleimides. Among the three series of macrocycles, the oxygen atom and thiophene containing linkers yielded molecules with higher inhibitory potency at GSK-3 beta (K(i)=0.011-0.079 microM) while the nitrogen atom containing linkers yielded molecules with lower potency (K(i)=0.150->1 microM). Compound 33 and 36 displayed 1-2 orders of magnitude selectivity at GSK-3 beta against CDK2, PKC beta II, Rsk3 and little or no inhibitions to the other 62 protein kinases. Compound 46 was at least 100-fold more selective towards GSK-3 beta than PKC beta II, and it had little or no activity against a panel of 65 protein kinases, almost behaved as a GSK-3 beta 'specific inhibitor'. All three compounds showed good potency in GS assay. Molecular docking studies were conducted in an attempt to rationalize the GSK-3 beta selectivity of azaindolylmaleimides. The high selectivity, inhibitory potency and cellular activities of these non-crown-ether typed molecules may provide them as a valuable pharmacological tools in elucidating the complex roles of GSK-3 beta in cell signaling pathways and the potential usage for the treatment of elevated level of GSK-3 beta involved diseases.

Synthesis and discovery of macrocyclic polyoxygenated bis-7-azaindolylmaleimides as a novel series of potent and highly selective glycogen synthase kinase-3beta inhibitors.

Attempts to design the macrocyclic maleimides as selective protein kinase C gamma inhibitors led to the unexpected discovery of a novel series of potent and highly selective glycogen synthase kinase-3beta (GSK-3beta) inhibitors. Palladium-catalyzed cross-coupling reactions were used to synthesize the key intermediates 17 and 22 that resulted in the synthesis of novel macrocycles. All three macrocyclic series (bisindolyl-, mixed 7-azaindoleindolyl-, and bis-7-azaindolylmaleimides) were found to have submicromolar inhibitory potency at GSK-3beta with various degrees of selectivity toward other protein kinases. To gain the inhibitory potency at GSK-3beta, the ring sizes of these macrocycles may play a major role. To achieve the selectivity at GSK-3beta, the additional nitrogen atoms in the indole rings may contribute to a significant degree. Overall, the bis-7-azaindolylmaleimides 28 and 29 exhibited little or no inhibitions to a panel of 50 protein kinases. Compound 29 almost behaved as a GSK-3beta specific inhibitor. Both 28 and 29 displayed good potency in GS cell-based assay. Molecular docking studies were conducted in an attempt to rationalize the GSK-3beta selectivity of azaindolylmaleimides.