Benzimidazole derivatives. Part 1: Synthesis and structure-activity relationships of new benzimidazole-4-carboxamides and carboxylates as potent and selective 5-HT4 receptor antagonists

Direct Synthesis of C4-Acyl Indoles via C-H Acylation

The direct synthesis of C4-acyl indoles deprived of C2 and C3 substituents has proven to be challenging, with scarce efficient synthetic routes being reported. Herein, we disclose a highly site-selective palladium-catalyzed C-H acylation for the construction of C4-acyl indoles via a Catellani-Lautens cyclization strategy. In addition, we systematically studied the ortho C-H acylation mechanism of iodoaniline through density functional theory (DFT) calculations and combined experimental results to elucidate the principle of high chemoselectivity brought by triazine benzoate as an acylation reagent.

Crystal structure of tetraaqua-bis(1,3-benzimidazol-3-ium-1,3-diacetato-κO)copper(II) hemihydrate, C22H27CuN4O12.50

C22H27CuN4O12.50, triclinic, P1̅ (no. 2), a = 7.3950(11) Å, b = 9.4574(15) Å, c = 9.6619(15) Å, α = 81.139(2)°, β = 75.457(3)°, γ = 77.974(3)°, V = 636.02(17) Å3, Z = 1, R gt(F) = 0.0371, wR ref(F 2) = 0.1020, T = 293 K.

Grindstone chemistry: protic ionic liquid-substrate tuned green synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity

An environmentally benign and highly substrate-protic ionic liquid controlled synthesis of 1,2-disubstituted and 2-substituted benzimidazoles with outstanding selectivity is demonstrated through grinding a mixture of OPD, aldehydes and catalyst.

Synthesis and biological screening of novel indolalkyl arenes targeting the serotonine transporter

A series of functionalized indolylalkylarenes 3-16(a and b) were synthesized and their affinities for the serotonin transporter were investigated in vitro. Compounds 3-12(a and b) were obtained by nucleophilic substitution of 3-(1H-indol-3-yl)propyl-4-methylbenzenesulfonates 2(a and b) with a series of azaheterocycles. Compounds 14-16(a and b) were prepared in a two-step sequence by reaction of 3-(1H-indol-3-yl)-2-methylpropanal with substituted 1,2-phenylenediamines. Compounds 3b, 4b, and 5b showed good binding affinities (K(i) = 33.0, 48.0, and 17 nM, respectively). The other synthesized compounds showed moderate or no affinity in the binding studies.

Discovery of TD-8954, a clinical stage 5-HT(4) receptor agonist with gastrointestinal prokinetic properties

The discovery of a series of 5-HT4 receptor agonists based on a novel 2-alkylbenzimidazole aromatic core is described. Optimization of the 2-substituent of the benzimidazole ring led to a series of agonists with subnanomolar binding affinity and moderate-to-high intrinsic activity relative to that of 5-HT. Consistent with our previously described multivalent design approach to this target, subsequent optimization of the linker and secondary binding group regions of the series afforded compound 18 (TD-8954), a potent and selective 5-HT4 receptor agonist in vitro with demonstrated prokinetic activity in multiple species.

Synthesis and pharmacological properties of a new hydrophilic and orally bioavailable 5-HT4 antagonist

5-HT4 receptor antagonists have been suggested to have clinical potential in treatment of atrial fibrillation, diarrhea-prone irritable bowel syndrome and urinary incontinence. Recently, the use of 5-HT4 antagonists has been suggested to have a therapeutic benefit in heart failure. Affinity for the hERG potassium ion channel and increased risk for prolonged QT intervals and arrhythmias has been observed for several 5-HT4 ligands. Serotonin may also have beneficial effects in the central nervous system (CNS) through stimulation of the 5-HT4 receptor, and reduced distribution of 5-HT4 antagonists to the CNS may therefore be an advantage. Replacing the amide and N-butyl side chain of the 5-HT4 receptor antagonist SB207266 with an ester and a benzyl dimethyl acetic acid group led to compound 9; a hydrophilic 5-HT4 antagonist with excellent receptor binding and low affinity for the hERG potassium ion channel. To increase oral bioavailability of carboxylic acid 9, two different prodrug approaches were applied. The tert-butyl prodrug 11 did not improve bioavailability, and LC-MS analysis revealed unmetabolized prodrug in the systemic circulation. The medoxomil ester prodrug 10 showed complete conversion and sufficient bioavailability of 9 to advance into further preclinical testing for treatment of heart failure.

Parallel and automated library synthesis of 2-long alkyl chain benzoazoles and azole[4,5-b]pyridines under microwave irradiation

A versatile route to 40-membered library of 2-long alkyl chain substituted benzoazoles (1 and 2) and azole[4,5-b]pyridines (3 and 4) via microwave-assisted combinatorial synthesis was developed. The reactions were carried out in both monomode and multimode microwave oven. With the latter, all reactions were performed in high-throughput experimental settings consisting of an 8 x 5 combinatorial library designed to synthesize 40 compounds. Each step, from the addition of reagents to the recovery of final products, was automated. The microwave-assisted N-long chain alkylation reactions of 2-alkyl-1H-benzimidazole (1) and 2-alkyl-1H-benzimidazole[4,5-b] pyridines (3) were also studied.

Synthesis and pharmacological evaluation of benzamide derivatives as selective 5-HT4 receptor agonists

It is thought that selective 5-HT(4) receptor agonists-such as 4-amino-5-chloro-2-methoxy-N-[1-(6-oxo-6-phenylhexyl)piperidin-4ylmethyl]benzamide (2)-have the ability to enhance both upper and lower gastrointestinal motility without any significant adverse effects. Modification of 2 was performed. Variation of the piperidin-4ylmethyl moiety of 2 led to a decrease in the binding affinity for the 5-HT(4) receptor. Following conversion of the carbonyl group on the benzoyl part to a hydroxyl or sulfoxide group, the binding affinity for the 5-HT(4) receptor was retained although the effect on defecation was reduced. Many of the 4-amino-5-chloro-2-methoxy-N-(piperidin-4ylmethyl)benzamides that had a ether or sulfide moiety in the side-chain part at the 1-position of the piperidine exhibited high affinity for the 5-HT(4) receptor. Among these, phenylthio 41c and benzylthio derivative 44 were selective 5-HT(4) receptor agonists, and had a similar effect on defecation to compound 2.

Drug Evolution Concept in Drug Design: 1. Hybridization Method†

A novel concept, "drug evolution", is proposed to develop chemical libraries that have a high probability of finding drugs or drug candidates. It converts biological evolution into chemical evolution. In this paper, we present "hybridization" drug evolution, which is the equivalent of sexual recombination of parental genomes in biological evolution. The hybridization essentially shuffles the building blocks of the parent drugs and ought to drug(s); no drug evolution can otherwise occur. We hybridized two drugs, benzocaine and metoclopramide and generated 16 molecules that include the parent drugs, four known drugs, and two molecules whose therapeutic activities are reported. The unusually high number of drugs and drug candidates in the library encourages high expectations of finding new drug(s) or drug candidate(s) within the remaining eight compounds. Interestingly, the therapeutic applications of the eight drugs or drug candidates in the library are fairly diverse as 38 therapeutic applications and 25 molecular targets are counted. Therefore, the library fits as a general chemical library for unspecified therapeutic activities. The hybridization of other two drugs, aspirin and cresotamide, is also described to demonstrate the generality of the method.

A single mutation in the 5-HT4 receptor (5-HT4-R D100(3.32)A) generates a Gs-coupled receptor activated exclusively by synthetic ligands (RASSL)

To better understand G-protein-coupled receptor (GPCRs) signaling, cellular and animal physiology, as well as gene therapy, a new tool has recently been proposed. It consists of GPCR mutants that are insensitive to endogenous ligands but sensitive to synthetic ligands. These GPCRs are called receptor activated solely by synthetic ligands (RASSL). Only two examples of such engineered receptors have been described so far: one G(i)-coupled (opioid receptors) and one G(s)-coupled (beta(2)-adrenergic receptors). Here, we describe the first RASSL related to serotonin receptors (D100(3.32)A G(s)-coupled 5-HT(4) receptor or 5-HT(4)-RASSL). 5-HT(4)-RASSL is generated by a single mutation, is totally insensitive to serotonin (5-HT), and still responds to synthetic ligands. These ligands have affinities in the range of nanomolar concentrations for the mutant receptor and exhibit full efficacy. More interestingly, two synthetic ligands behave as antagonists on the wild type but as agonists on the 5-HT(4)-RASSL.

New benzo[h][1,6]naphthyridine and azepino[3,2-c]quinoline derivatives as selective antagonists of 5-HT4 receptors: binding profile and pharmacological characterization

A series of benzo[h][1,6]naphthyridine and azepino[3,2-c]quinoline derivatives were prepared and evaluated to determine the necessary requirements for high affinity on the 5-HT(4) receptors and high selectivity versus other receptors. The compounds were synthesized by substituting the chlorine atom of benzonaphthyridines and azepinoquinolines with various N-alkyl-4-piperidinylmethanolates. They were evaluated in binding assays with [(3)H]GR 113808 as the 5-HT(4) receptor radioligand. The affinity values (K(i) or inhibition percentages) depended upon the substituent on the aromatic ring on one hand and the substituent on the lateral piperidine chain on the other hand. A chlorine atom produced a marked drop in activity while a N-propyl or N-butyl group gave compounds with nanomolar affinities (1 < K(i) < 10 nM). Among the most potent ligands (3a, 4a, 5a), 4a was selected on the basis of its high affinity and selectivity for pharmacological screening and was evaluated in vivo in specific tests. This compound reveals itself as an antagonist/low partial agonist in the COS-7 cells stably expressing the 5-HT(4(a)) receptor. Derivative 4a also showed in vivo potent analgesic activity in the writhing test at very low doses.

Benzimidazole derivatives. 3. 3D-QSAR/CoMFA model and computational simulation for the recognition of 5-HT(4) receptor antagonists

A three-dimensional quantitative structure-affinity relationship study (3D-QSAR), using the comparative molecular field analysis (CoMFA) method, and subsequent computational simulation of ligand recognition have been successfully applied to explain the binding affinities for the 5-HT(4) receptor (5-HT(4)R) of a series of benzimidazole-4-carboxamides and carboxylates derivatives 1-24. The K(i) values of these compounds are in the range from 0.11 to 10 000 nM. The derived 3D-QSAR model shows high predictive ability (q(2) = 0.789 and r(2) = 0.997). Steric (contribution of 43.5%) and electrostatic (50.3%) fields and solvation energy (6.1%) of this novel class of 5-HT(4)R antagonists are relevant descriptors for structure-activity relationships. Computational simulation of the complexes between the benzimidazole-4-carboxamide UCM-21195 (5) and the carboxylate UCM-26995 (21) and a 3D model of the transmembrane domain of the 5-HT(4)R, constructed using the reported crystal structure of rhodopsin, have allowed us to define the molecular details of the ligand-receptor interaction that includes (i) the ionic interaction between the NH group of the protonated piperidine of the ligand and the carboxylate group of Asp(3.32), (ii) the hydrogen bond between the carbonyl oxygen of the ligand and the hydroxyl group of Ser(5.43), (iii) the hydrogen bond between the NH group of Asn(6.55) and the aromatic ring of carboxamides or the ether oxygen of carboxylates, (iv) the interaction of the electron-rich clouds of the aromatic ring of Phe(6.51) and the electron-poor hydrogens of the carbon atoms adjacent to the protonated piperidine nitrogen of the ligand, and (v) the pi-sigma stacking interaction between the benzimidazole system of the ligand and the benzene ring of Tyr(5.38). Moreover, the noticeable increase in potency at the 5-HT(4)R sites, by the introduction of a chloro or bromo atom at the 6-position of the aromatic ring, is attributed to the additional electrostatic and van der Waals interaction of the halogen atom in a small cavity located between transmembrane domains 5 and 6.

Evaluation of lipophilicity of some benzimidazole and benztriazole derivatives by RP HPTLC and PCA

The lipophilic character of some benzimidazole and benztriazole derivatives was studied. The classical R(Mo) values were compared with the factors scores obtained by principal component analysis (PCA) based also onto the TLC retention data. The very high correlation between the R(Mo) values and slopes (specific hydrophobic surface area) indicated as usually that this group of compounds could be considered as a homologous series independently of their structural heterogeneity. It is emphasized once again that this procedure can not be a rational and objective way for congeneric studies because always there is a high correlation between slope and intercept. The reliability of the factor scores values as lipophilic indices are shown by their high correlation with the classical R(Mo) values. In addition, the 'lipophilicity chart' described by the first two components has the effect of separating compounds from each other most effectively from the congeneric aspect point of view. The most lipophilic compounds appeared to be the benzimidazole derivatives.

3-D-QSAR/CoMFA and recognition models of benzimidazole derivatives at the 5-HT(4) receptor

3-D-QSAR/CoMFA methodology and computational simulation of ligand recognition have been successfully applied to explain the binding affinities of a series of benzimidazole derivatives 1-24 acting at serotonin 5-HT(4)Rs. Both derived computational models have facilitated the identification of the structural elements of the ligands that are key to high 5-HT(4)R affinity. The results provide the tools for predicting the affinity of related compounds, and for guiding the design and synthesis of new ligands with predetermined affinities and selectivity.

Benzimidazole derivatives. 2. Synthesis and structure-activity relationships of new azabicyclic benzimidazole-4-carboxylic acid derivatives with affinity for serotoninergic 5-HT(3) receptors

A new series of azabicyclic benzimidazole-4-carboxamides 2-21 and -carboxylates 22-30 were synthesized and evaluated for binding affinity at serotoninergic 5-HT(3) and 5-HT(4) receptors in the CNS. Most of the synthesized compounds exhibited high or very high affinity for the 5-HT(3) binding site and low to no significant affinity for the 5-HT(4) receptor. SAR observations indicated that a halogen atom at the 6-position and a nitro group at the 7-position of the benzimidazole ring is the best substitution pattern for 5-HT(3) affinity and 5-HT(3)/5-HT(4) selectivity, as well as no substitution in this ring. (S)-(-)-N-(Quinuclidin-3-yl)benzimidazole-4-carboxamides 2, 8, and 14 bound at central 5-HT(3) sites with high affinity (K(i) = 2.6, 0. 13, and 1.7 nM, respectively) and excellent selectivity over serotonin 5-HT(4) and 5-HT(1A) receptors (K(i) > 1000-10000 nM). Furthermore, these new 5-HT(3) receptor ligands were pharmacologically characterized as potent and selective 5-HT(3) antagonists in the isolated guinea pig ileum (pA(2) = 9.6, 9.9, and 9.1, respectively).