Cardiotonic agents. 2. (Imidazolyl)aroylimidazolones, highly potent and selective positive inotropic agents

C-X (X = N, O) Cross-Coupling Reactions Catalyzed by Copper-Pincer Bis(N-Heterocyclic Carbene) Complexes

Over the last two decades, N-heterocyclic carbene (NHC)–copper catalysts have received considerable attention in organic synthesis. Despite the popularity of copper complexes containing monodentate NHC ligands and recent development of poly(NHC) platforms, their application in C–C and C–heteroatom cross-coupling reactions has been limited. Recently, we reported an air-assisted Sonogashira-type cross-coupling catalyzed by well-defined cationic copper-pincer bis(NHC) complexes. Herein, we report the application of these complexes in Ullmann-type C–X (X = N, O) coupling of azoles and phenols with aryl halides in a relatively short reaction time. In contrast to other well-defined copper(I) catalysts that require an inert atmosphere for an efficient C–X coupling, the employed Cu(I)-pincer bis(NHC) complexes provide good to excellent yields in air. The air-assisted reactivity, unlike that in the Sonogashira reaction, is also affected by the base employed and the reaction time. With Cs₂CO₃ and K₂CO₃, the oxygen-generated catalyst is more reactive than the catalyst formed under argon in a short reaction time (12 h). However, the difference in reactivity is compromised after a 24 h reaction with K₂CO₃. The efficient pincer Cu-NHC/O₂/Cs₂CO₃ system provides great to excellent cross-coupling yields for electronically diverse aryl iodides and imidazole derivatives. The catalyst scope is controlled by a balance between nucleophilicity, coordinating ability, and the steric hindrance of aryl halides and N-/O-nucleophiles.

Imidazolyl-phenyl (IMP) anions: a modular structure for tuning solubility and coordinating ability

The effect of counteranion upon a cation's solution-phase reactivity depends on a subtle interplay of weak interactions.

Synthesis and characterization of 8-ethynyl-1,3-dihydro-benzo[b][1,4]diazepin-2-one derivatives: part 2. New potent non-competitive metabotropic glutamate receptor 2/3 antagonists

A series of 1,3-dihydro-benzo[b][1,4]diazepin-2-one derivatives was evaluated as non-competitive mGluR2/3 antagonists. Replacement of a cyano group by a five-membered heterocycle produced compounds inhibiting the binding of [(3)H]-LY354740 to rat mGluR2 with low nanomolar affinity and consistent functional effect at both mGluR2 and mGluR3. Further modification to improve the physicochemical properties led eventually to compounds with the ability to reverse LY354740-mediated inhibition of field excitatory postsynaptic potentials in the rat dentate gyrus.

Novel Heterocyclic Trans Olefin Analogues of N-{4-[4-(2,3-Dichlorophenyl)piperazin-1-yl]butyl}arylcarboxamides as Selective Probes with High Affinity for the Dopamine D3 Receptor

Dopamine D3 receptor subtypes have been hypothesized to play a pivotal role in modulating the reinforcing and drug-seeking effects induced by cocaine. However, definitive pharmacological investigations have been hampered by the lack of highly D3 receptor selective compounds that can be used in vivo. To address this problem, the potent and D3-receptor-selective antagonist NGB 2904 (1, 9H-fluorene-2-carboxylic acid {4-[(2,3-dichlorophenyl)-piperazin-1-yl]-butyl}-amide, Ki (hD3) = 2.0 nM, Ki (hD2L) = 112 nM, D2/D3 selectivity ratio of 56) was chosen as a lead structure for chemical modification in an attempt to reduce its high lipophilicity (c log D = 6.94) while optimizing D3 receptor binding affinity and D2/D3 selectivity. A series of >30 novel analogues were synthesized, and their binding affinities were evaluated in competition binding assays in HEK 293 cells transfected with either D2(L), D3, or D4 human dopamine receptors using the high affinity, selective D2-like receptor antagonist (125)I-IABN. Structural diversity in the aryl amide end of the molecule was found to have a major influence on (sub)nanomolar D3 receptor affinity and D2/D3 selectivity, which was optimized using a more rigid trans-butenyl linker between the aryl amide and the piperazine. Several analogues demonstrated superior D3 receptor binding affinities and selectivities as compared to the parent ligand. Compound 29 (N-{4-[4-(2,3-dichlorophenyl)-piperazin-1-yl]-trans-but-2-enyl}-4-pyridine-2-yl-benzamide) displayed the most promising pharmacological profile (Ki (hD3) = 0.7 nM, Ki (hD2L) = 93.3 nM, D2/D3 selectivity ratio of 133). In addition, this ligand inhibited quinpirole stimulation of mitogenesis at human dopamine D3 receptors transfected into Chinese hamster ovary (CHO) cells, with an EC50 value of 3.0 nM. Compound 29 was a nearly 5 times more potent antagonist at the D3 receptor than 1 (EC50 = 14.4 nM). Moreover, a decrease in c log D value of approximately 2 orders of magnitude was determined for this novel D3-receptor-preferring ligand, compared to 1. In summary, chemical modification of 1 has resulted in compounds with high affinity and selectivity for D3 receptors. The most promising candidate, compound 29, is currently being evaluated in animal models of cocaine abuse and will provide an important tool with which to elucidate the role of D3 receptors in drug reinforcement in vivo.

Quantitative structure-activity relationships of cardiotonic agents

Quantitative structure-activity relationships (QSARs) of different cardiotonic agents are presented. A critical analysis of all QSARs provides a very vivid picture of the mechanisms of varying cardiotonic agents. The cardiotonics can be broadly put into 2 categories: cardiac glycosides and nonglycoside cardiotonics, which include phosphodiesterase of type III (PDE III) inhibitors, sympathomimetic (adrenergic) stimulants, A1-selective adenosine antagonists, Ca2+ channel activators and vasopressin antagonists. For cardiac glycosides, QSARs reveal that the position of carbonyl oxygen in their lactone moiety and shifting of the lactone ring from its original position or its replacement by another group would be crucial for their activity. The carbonyl group or its isostere like CN is indicated to be the sole binding entity and the hydrogen bonding through this group is considered to be the most likely binding force. For nonglycoside cardiotonics that include PDE III inhibitors and A1-selective antagonists, a five-point model has been established for their activity, the salient features of which are: (1) the presence of a strong dipole, (2) an adjacent acidic proton, (3) a methyl-sized lipophilic space, (4) a relatively flat overall topography and (5) a basic or hydrogen-bond acceptor site opposite to the dipole. For Ca2+ channel activators, the importance of steric, electrostatic, lipophilic and hydrogen-bonding properties of molecules is indicated, while for vasopressin antagonists the lipophilic and electronic properties are suggested to be the most important.

Synthesis of conformationally constrained 5,6,7, 8-Tetrahydroimidazo[1,5-a]pyridine inhibitors of farnesyltransferase

[reaction: see text] Synthesis of the 8-amino-5,6,7,8-tetrahydroimidazo[1,5-a]pyridine ring system was accomplished by intramolecular cyclization of an iminium ion, derived from condensation of an amine and a substituted gamma-(1-imidazolyl)butyraldehyde. The reaction was used to produce conformationally restricted farnesyltransferase inhibitor analogues which exhibit improved in vivo metabolic stability.

A topographical model for the c-AMP phosphodiesterase III active site

With this minireview, concepts about how c-AMP and various inhibitor molecules interact with the phosphodiesterases seem to have come full-circle. It will be proposed and elaborated herein that an understanding of SAR for the newest, "second generation" PDE inhibitors is best accomplished by adopting a model that supposes that these compounds are transition state inhibitors. The analysis finds an interesting parallel with early studies where it was recognized that c-AMP adopts a trigonal bipyramid transition state during hydrolysis. The dynamic interaction of ligands with the phosphodiesterase enzymes will also be made evident when simple algebraic expressions are shown to be inadequate for predicting inhibitor potencies. The latter are apparently complicated by cooperative or synergistic relationships that occur among the various binding sites within the receptor. Finally, implications that can be derived from certain topographical features of the model are discussed relative to a range of potential therapeutic indications.

Antiarrhythmic peptide has no direct cardiac actions

The electrophysiologic, inotropic, and muscarinic effects of antiarrhythmic peptide (AAP) were examined in canine cardiac Purkinje fibers, ferret papillary muscle, and canine cardiac membranes, respectively. Aside from a prolongation of time to peak force in papillary muscle, no biologically significant effects of AAP could be determined in any preparation, suggesting that its antiarrhythmic effects are not mediated by direct membrane actions.