New nonpeptide angiotensin II receptor antagonists. 2. Synthesis, biological properties, and structure-activity relationships of 2-alkyl-4-(biphenylylmethoxy)quinoline derivatives

Quinoline Hydrazide/Hydrazone Derivatives: Recent Insights on Antibacterial Activity and Mechanism of Action

Antibiotics are becoming gradually ineffective due to drug resistance, leading to greater difficulty in the treatment of infectious diseases. Therefore, the development of new chemical entities with different mechanisms of action is essential in the fight against resistant microorganisms. Various studies have shown that quinoline hydrazide/hydrazone derivatives possess several biological activities, such as antimalarial, antitubercular, anticancer, anti-inflammatory, and antimicrobial. Among these activities, the antibacterial activity of quinoline hydrazide/hydrazone derivatives is noteworthy. The synthetic flexibility of the quinoline ring has led to the development of a wide range of structurally diverse quinoline hydrazide/hydrazone derivatives, which can act at various bacterial targets such as DNA gyrase, glucosamine-6-phosphate synthase, enoyl ACP reductase, and 3-ketoacyl ACP reductase. This review emphasizes the antibacterial potential of various reported quinoline hydrazide/hydrazone derivatives based on substitution in the quinoline ring. The antibacterial activity of various metal-quinoline hydrazide/hydrazone complexes is also discussed. The aim of this review is to assemble and scrutinize the latest reports in this promising area of drug development.

Sulfone-Mediated SNAr Reaction as a Powerful Tool for the Synthesis of 4-Quinolinyl Ethers and More-Application to the Synthesis of HCV NS3/4a Protease Inhibitor

An efficient general methodology for the synthesis of 4-quinolinyl ethers is demonstrated via a highly reactive S_NAr reaction of 4-quinolinyl sulfones with a range of structurally diversified 1°, 2°, and 3° alcohols with a wide substrate scope and high yields. By adapting this methodology, a convergent synthesis of a complex target of HCV NS3/4a protease inhibitor BI 201420 was accomplished.

Integration of multi-scale molecular modeling approaches with experiments for the in silico guided design and discovery of novel hERG-Neutral antihypertensive oxazalone and imidazolone derivatives and analysis of their potential restrictive effects on cell proliferation

AT1 antagonists is the most recent drug class of molecules against hypertension and they mediate their actions through blocking detrimental effects of angiotensin II (A-II) when acts on type I (AT1) A-II receptor. The effects of AT1 antagonists are not limited to cardiovascular diseases. AT1 receptor blockers may be used as potential anti-cancer agents - due to the inhibition of cell proliferation stimulated by A-II. Therefore, AT1 receptors and the A-II biosynthesis mechanisms are targets for the development of new synthetic drugs and therapeutic treatment of various cardiovascular and other diseases. In this work, multi-scale molecular modeling approaches were performed and it is found that oxazolone and imidazolone derivatives reveal similar/better interaction energy profiles compared to the FDA approved sartan molecules at the binding site of the AT1 receptor. In silico-guided designed hit molecules were then synthesized and tested for their binding affinities to human AT1 receptor in radioligand binding studies, using [¹²⁵I-Sar¹-Ile⁸] AngII. Among the compounds tested, 19d and 9j molecules bound to receptor in a dose response manner and with relatively high affinities. Next, cytotoxicity and wound healing assays were performed for these hit molecules. Since hit molecule 19d led to deceleration of cell motility in all three cell lines (NIH3T3, A549, and H358) tested in this study, this molecule is investigated in further tests. In two cell lines (HUVEC and MCF-7) tested, 19d induced G2/M cell cycle arrest in a concentration dependent manner. Adherent cells detached from the plates and underwent cell death possibly due to apoptosis at 19d concentrations that induced cell cycle arrest.

Structure-based design of hERG-neutral antihypertensive oxazalone and imidazolone derivatives

Angiotensin II receptor type 1 (AT1) antagonists are the most recent drug class against hypertension. Recently first crystal structure of AT1 receptor is deposited to the protein data bank (PDB ID: 4YAY). In this work, several molecular screening methods such as molecular docking and de novo design studies were performed and it is found that oxazolone and imidazolone derivatives reveal similar/better interaction energy profiles compared to the FDA approved sartan molecules at the binding site of the AT1 receptor. A database consisting of 3500-fragments were used to enumerate de novo designed imidazolone and oxazolone derivatives and hereby more than 50000 novel small molecules were generated. These derivatives were then used in high throughput virtual screening simulations (Glide/HTVS) to find potent hit molecules. In addition, virtual screening of around 18 million small drug-like compounds from ZINC database were screened at the binding pocket of the AT1 receptor via Glide/HTVS method. Filtered structures were then used in more sophisticated molecular docking simulations protocols (i.e., Glide/SP; Glide/XP; Glide/IFD; Glide/QPLD, and GOLD). However, the K⁺ ion channel/drug interactions should also be considered in studies implemented in molecular level against their cardiovascular risks. Thus, selected compounds with high docking scores via all diverse docking algorithms are also screened at the pore domain regions of human ether-a-go-go-related gene (hERG1) K⁺ channel to remove the high affinity hERG1 blocking compounds. High docking scored compounds at the AT1 with low hERG1 affinity is considered for long molecular dynamics (MD) simulations. Post-processing analysis of MD simulations assisted for better understanding of molecular mechanism of studied compounds at the binding cavity of AT1 receptor. Results of this study can be useful for designing of novel and safe AT1 inhibitors.

Improved Sommelet Reaction Catalysed by Lanthanum Triflate

An improved Sommelet reaction for the synthesis of araldehydes from benzyl halides and hexamethylenetetramine was achieved employing lanthanum triflate (3 mol%) as catalyst in water with sodium dodecyl sulfate (SDS, 2 wt%) as solubiliser. Good to excellent yields were obtained in most of the 18 examples.

Reduced graphs and their applications in chemoinformatics

Reduced graphs provide summary representations of chemical structures by collapsing groups of connected atoms into single nodes while preserving the topology of the original structures. This chapter reviews the extensive work that has been carried out on reduced graphs at The University of Sheffield and includes discussion of their application to the representation and search of Markush structures in patents, the varied approaches that have been implemented for similarity searching, their use in cluster representation, the different ways in which they have been applied to extract structure-activity relationships and their use in encoding bioisosteres.

An efficient synthesis of a rationally designed 1,5 disubstituted imidazole AT(1) angiotensin II receptor antagonist: reorientation of imidazole pharmacophore groups in losartan reserves high receptor affinity and confirms docking studies

A new 1,5 disubstituted imidazole AT(1) Angiotensin II (AII) receptor antagonist related to losartan with reversion of butyl and hydroxymethyl groups at the 2-, 5-positions of the imidazole ring was synthesized and evaluated for its antagonist activity (V8). In vitro results indicated that the reorientation of butyl and hydroxymethyl groups on the imidazole template of losartan retained high binding affinity to the AT(1) receptor concluding that the spacing of the substituents at the 2,5- positions is of primary importance. The docking studies are confirmed by binding assay results which clearly show a comparable binding score of the designed compound V8 with that of the prototype losartan. An efficient, regioselective and cost effective synthesis renders the new compound as an attractive candidate for advanced toxicological evaluation and a drug against hypertension.

Synthesis, binding studies and in vivo biological evaluation of novel non-peptide antihypertensive analogues

AT(1) antagonists (SARTANs) constitute the last generation of drugs for the treatment of hypertension, designed and synthesized to mimic the C-terminal segment of the vasoconstrictive hormone angiotensin II (AngII). They exert their action by blocking the binding of AngII on the AT(1) receptor. Up to date eight AT(1) antagonists have been approved for the regulation of high blood pressure. Although these molecules share common structural features and are designed to act under the same mechanism, they have differences in their pharmacological profiles and antihypertensive efficacy. Thus, there is still a need for novel analogues with better pharmacological and financial profiles. An example of a novel synthetic non peptide AT(1) antagonist which devoids the classical template of SARTANs is MM1. In vivo studies showed that MMK molecules, which fall in the same class of MM1, had a significant antihypertensive (40-80% compared to the drug losartan) activity. However, in vitro affinity studies showed that losartan has considerably higher affinity. The theoretical docking studies showed that MM1 acts on the same site of the receptor as losartan. They exert hydrophobic interactions with amino acid Val108 of the third helix of the AT(1) receptor and other hydrophobic amino acids in spatial vicinity. In addition, losartan favours multiple hydrogen bondings between its tetrazole group with Lys199. These additional interactions may in part explain its higher in vitro binding affinity.

Further development of reduced graphs for identifying bioactive compounds

Reduced graphs provide summary representations of chemical structures. Here, a variety of different types of reduced graphs are compared in similarity searches. The reduced graphs are found to give comparable performance to Daylight fingerprints in terms of the number of active compounds retrieved. However, no one type of reduced graph is found to be consistently superior across a variety of different data sets. Consequently, a representative set of reduced graphs was chosen and used together with Daylight fingerprints in data fusion experiments. The results show improved performance in 10 out of 11 data sets compared to using Daylight fingerprints alone. Finally, the potential of using reduced graphs to build SAR models is demonstrated using recursive partitioning. An SAR model consistent with a published model is found following just two splits in the decision tree.

Crystal structure of the alcoholates and the ansolvate of PNU-97018, an angiotensin II receptor antagonist

The title compound, PNU-97018 [systemic name: 2-butyl-3,6,7,8,9,11-hexahydro-6,9-dimethyl-3-([2'-(2H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl)-6,9-ethano-4H-imidazo[4,5-d]-pyridazino[1,2-a]pyridazin-4-one] is a newly developed angiotensin II receptor antagonist. The compound and its methanolate and ethanolate were characterized by X-ray crystallography and thermal analysis. The methanolate and ethanolate crystals have an almost identical molecular conformation and crystal packing. In both alcoholates, each alcohol molecule is fixed to the compound with a molar ratio of 1 : 1 by a hydrogen bond between the hydroxyl group of the alcohol molecule and the tetrazole group of the compound. The hydroxyl group of each alcohol molecule further links with the imidazole ring of the neighboring compound by hydrogen bond to form a hydrogen-bond network in both alcoholates. A tunnel-like structure that includes alcohol molecules is formed in each alcoholate. The ansolvate crystal showed completely different thermal and X-ray crystallographic characteristics from the alcoholates, where the compound molecules were directly linked by hydrogen bonds between the tetrazole group of a molecule and the imidazole ring of the neighboring molecule. The position of the hydrogen atom in the tetrazole ring was different between the ansolvate and alcoholates. Unlike alcoholates, a layer structure stacked on the b-c plane was observed in the ansolvate crystal. It was concluded that the molecular conformation and the arrangement of the compound molecules were largely different between ansolvate and alcoholate crystals.

Prospective identification of biologically active structures by topomer shape similarity searching

The principle of bioisosterism-similarly shaped molecules are more likely to share biological properties than are other molecules-has long helped to guide drug discovery. An algorithmic implementation of this principle, based on shape comparisons of a single rule-generated "topomer" conformation per molecule, had been found to be the descriptor most consistently predictive of similar biological properties, in retrospective studies, and also to be well-suited for searching large (>10(12)) "virtual libraries" of potential reaction products. Therefore a prospective trial of this shape similarity searching method was carried out, with synthesis of 425 compounds and testing of them for inhibition of binding of angiotensin II (A-II). The 63 compounds that were identified by shape searching as most similar to any of four query structures included all of the seven compounds found to be highly active, with none of the other 362 structures being highly active (p < 0.001). Additional consistent relations (p < 0.05) were found, among all 425 compounds, between the degree of shape similarity to the nearest query structure and the frequency of various levels of observed activity. Known "SAR" (rules specifying structural features required for A-II antagonism) were also regenerated within the biological data for the 63 shape similar structures.

An effort to understand the molecular basis of hypertension through the study of conformational analysis of losartan and sarmesin using a combination of nuclear magnetic resonance spectroscopy and theoretical calculations

Losartan is the first recently approved drug against hypertension disease that competes with the biological action of angiotensin II (AII) at the AT1 receptor. Its design was based on the mimicry of the C-terminal segment of AII. Due to the biological significance of Losartan, its structure elucidation and conformational properties are reported as determined by NMR spectroscopy and computational analysis. In addition, molecular modeling of the peptide Sarmesin [Sar1Tyr(OMe)4AII], a competitive antagonist of AII, was also developed based on NMR and computational analysis data. Sarmesin's C-terminal was used as a template for superimposition with specific molecular features of interest in the structure of Losartan such as the conformation of biphenyltetrazole, the n-butyl chain, and the orientation of hydroxymethylimidazole relative to the biphenyl template. The major conclusions derived from this study are the following: (a) Sarmesin, like the AII superagonist [Sar1]AII, adopts a conformation which keeps in close proximity the key amino acids Sar1 (or Arg2)-Tyr(OMe)4-His6-Phe8. (b) Losartan favors a low-energy conformation in which imidazole and tetrazole rings are placed in the opposite site relative to the spacer phenyl ring plane; the hydroxymethyl group is placed away from the spacer phenyl ring, the alkyl chain is oriented above the spacer phenyl ring, and the two phenyl rings deviate approximately 60 degrees from being coplanar. (c) Overlay of the C-terminal region of Sarmesin with Losartan using equivalent groups revealed an excellent match. (d) Interestingly, the matching between enantiomeric structures of Losartan was not equivalent, proposing that the chirality of this molecule is significant in order to exert its biological activity. These findings open a new avenue for synthetic chemists to design and synthesize peptidomimetic drugs based on the C-terminal segment of the proposed model of Sarmesin. The new candidate drug molecules are not restricted to structurally resemble Losartan as the design is hitherto focused.

Synthesis of biphenylyltetrazole derivatives of 1-aminopyrroles as angiotensin II antagonists

Based on preliminary molecular modelling study, the synthesis of two different classes of biphenylyltetrazole derivatives of 1-aminopyrroles, as potentially active non-peptide angiotensin II (AII) antagonists, is reported. Some NH-Boc protected l-aminopyrroles were deprotected, N-acylated, N-alkylated with 5-[4'-bromomethyl-1,1'-biphenyl-2-yl]-1-triphenylmethyl-1H-tetrazo le, and then detritylated to give the first class of title compounds. Other 1-NH-Boc protected 1,2-diaminopyrroles were regioselectively subjected to the 1-alkylation with 5-[4'-bromomethyl-1,1'-biphenyl-2-yl]-1-triphenylmethyl-1H-tetrazo le, to the acylation of the amino group at 2-position of the pyrrole ring, and then to the detritylation process to yield the second class of title compounds.

Phosphodiesterase inhibitory properties of losartan. Design and synthesis of new lead compounds

A 4-centre PDE4 pharmacophore search has been carried out in several 3D-databases containing compounds belonging to different therapeutic areas. Losartan, an angiotensin-II antagonist, has been identified as a new lead compound for developing PDE4 inhibitors. New families of compounds derived from losartan has been synthesized and their PDE inhibition has been measured.

A 3D QSAR CoMFA study of non-peptide angiotensin II receptor antagonists

A series of non-peptide angiotensin II receptor antagonists was investigated with the aim of developing a 3D QSAR model using comparative molecular field analysis descriptors and approaches. The main goals of the study were dictated by an interest in methodologies and an understanding of the binding requirements to the AT1 receptor. Consistency with the previously derived activity models was always checked to contemporarily test the validity of the various hypotheses. The specific conformations chosen for the study, the procedures invoked to superimpose all structures, the conditions employed to generate steric and electrostatic field values and the various PCA/PLS runs are discussed in detail. The effect of experimental design techniques to select objects (molecules) and variables (descriptors) with respect to the predictive power of the QSAR models derived was especially analysed.

A genetic algorithm for flexible molecular overlay and pharmacophore elucidation

A genetic algorithm (GA) has been developed for the superimposition of sets of flexible molecules. Molecules are represented by a chromosome that encodes angles of rotation about flexible bonds and mappings between hydrogen-bond donor proton, acceptor lone pair and ring centre features in pairs of molecules. The molecule with the smallest number of features in the data set is used as a template, onto which the remaining molecules are fitted with the objective of maximising structural equivalences. The fitness function of the GA is a weighted combination of: (i) the number and the similarity of the features that have been overlaid in this way; (ii) the volume integral of the overlay; and (iii) the van der Waals energy of the molecular conformations defined by the torsion angles encoded in the chromosomes. The algorithm has been applied to a number of pharmacophore elucidation problems, i.e., angiotensin II receptor antagonists, Leu-enkephalin and a hybrid morphine molecule, 5-HT1D agonists, benzodiazepine receptor ligands, 5-HT3 antagonists, dopamine D2 antagonists, dopamine reuptake blockers and FKBP12 ligands. The resulting pharmacophores are generated rapidly and are in good agreement with those derived from alternative means.

Derivation of a 3D pharmacophore model for the angiotensin-II site one receptor

A systematic search has been used to derive a hypothesis for the receptor-bound conformation of A-II antagonists at the AT1 receptor. The validity of the pharmacophore hypothesis has been tested using CoMFA, which included 50 diverse A-II antagonists, spanning four orders of magnitude in activity. The resulting cross-validated R2 of 0.64 (conventional R2 of 0.76) is indicative of a good predictive model of activity, and has been used to estimate potency for a variety of non-peptidyl antagonists. The structural model for the non-peptide has been compared with respect to the natural substrate, A-II, by generating peptide to non-peptide overlays.

Differentiation between binding sites for angiotensin II and nonpeptide antagonists on the angiotensin II type 1 receptors

To characterize binding sites for nonpeptide angiotensin antagonists on the human angiotensin II receptor type 1 (AT1 receptor) we have systematically exchanged segments of the human receptor with corresponding segments from a homologous Xenopus laevis receptor, which does not bind the nonpeptide compounds. Substitution of transmembrane segment VII of the human AT1 receptor dramatically reduced the binding affinity of all of the 11 nonpeptide antagonists tested (55- to > 2000-fold) with no effect on the binding of angiotensin. The affinity for the nonpeptide compounds decreased additionally one order of magnitude when transmembrane segment VI and the connecting extracellular loop 3 from the Xenopus receptor were also introduced into the human AT1 receptor. Exchanges of smaller segments and single residues in transmembrane segments VI and VII and extracellular loop 3 revealed that the binding of nonpeptide antagonists was dependent on nonconserved residues located deep within the transmembrane segments VI and VII, in particular Asn295 in transmembrane segment VII. Surprisingly, all exchanges in transmembrane segment VII, including the Asn295 to Ser substitution, had a more pronounced effect on the binding of the competitive antagonists relative to the insurmountable antagonists. It is concluded that the binding mode for peptide and nonpeptide ligands on the AT1 receptor is rather different and that competitive and insurmountable antagonists presumably bind to overlapping but distinct sites located in transmembrane segments VI and VII.

Vasomotor responses in cyclosporin A-treated rats after chronic angiotensin blockade

Chronic angiotensin-converting enzyme (ACE) inhibition prevents endothelial dysfunction in hypertension and hypercholesterolemia. Long-term treatment with cyclosporin A impairs endothelium-dependent relaxations and augments contractions to angiotensin II in the rat aorta. The present study compares vasomotor responses to several vasoconstrictor and dilator stimuli after 6 weeks of oral treatment with either the angiotensin-converting enzyme inhibitor lisinopril (10 mg/kg per day), the angiotensin subtype 1 receptor antagonist D 8731 (10 mg/kg per day), cyclosporin A (15 mg/kg per day), or a combination of cyclosporin A with lisinopril or D 8731 (n = 15 rats per group). Twenty-four hours after the last treatment, aortic rings were mounted in organ chambers for measurement of isometric force. Endothelium-dependent relaxations to acetylcholine and calcium ionophore were impaired by cyclosporin A but not affected by the vasodilators. Cyclosporin A-induced endothelial dysfunction was prevented by cotreatment with lisinopril or D 8731. Relaxations to nitroglycerin, SIN-1, and forskolin were not affected by any treatment. Contractions to phenylephrine and serotonin were reduced by lisinopril but not by D 8731. In contrast, contractions to angiotensin II were augmented by cyclosporin A, lisinopril, and the combination of both but not by D 8731 or D 8731 plus cyclosporin A. The data suggest a role for angiotensin II in cyclosporin A-induced endothelial dysfunction. Chronic ACE inhibition reduces overall smooth muscle contractility. The selective augmentation of angiotensin II effects by ACE inhibition and cyclosporin A suggests upregulation of angiotensin receptors in the aortic smooth muscle by these treatments. Chronic angiotensin subtype 1 receptor blockade does not appear to affect angiotensin receptor function.

A 3D QSAR approach to the search for geometrical similarity in a series of nonpeptide angiotensin II receptor antagonists

A 3D QSAR methodology based on the combined use of conformational analysis and chemometrics was applied to perform a comparative analysis of the 3D conformational features of 13 nonpeptide angiotensin II receptor antagonists showing different levels of binding affinity. Conformational analysis by using a molecular mechanics MM2 method was carried out for each of these structures to obtain conformational minima. These minima were described by ten interatomic distances which define the relative spatial disposition of five significant atoms belonging to relevant functional groups present in all the 13 molecules. The structure-activity relationship between the interatomic distances and the biological activity was then assessed by using chemometric methods (cluster analysis, principal component analysis, classification methods). With our indirect approach based on the search for geometrical similarity it was possible, even though structural information on the receptor active site was lacking, to identify the 3D geometrical requirements for the binding affinity of nonpeptide angiotensin II receptor inhibitors.

The renin-angiotensin system in the brain: an update 1993

The renin-angiotensin system is considered to be one of the most important hormonal systems in the regulation of blood pressure and body fluid homeostasis. Ever since this system has been demonstrated to be present also in the brain, vast efforts have been made in investigating its central impact and function. The last few years, and especially the development of non-peptidic angiotensin II receptor subtype specific antagonists and the subsequent pharmacological characterization of these subtypes, brought this field of research a large step forward. This progress also might have opened up new avenues of developing highly specific anti-hypertensive drugs and thereby new ways of treating hypertension. This paper intends to provide a summary of the knowledge about the brain renin-angiotensin system accumulated during recent years; an update 1993.