Alpha1-adrenoceptor antagonists. 6. Structural optimization of pyridazinone-arylpiperazines. Study of the influence on affinity and selectivity of cyclic substituents at the pyridazinone ring and alkoxy groups at the arylpiperazine moiety

Synthesis, spectroscopy, crystal structure, TGA/DTA study, DFT and molecular docking investigations of (E)-4-(4-methylbenzyl)-6-styrylpyridazin-3(2H)-one

In this study, we present the synthesis of novel pyridazin-3(2H)-one derivative namely (E)-4-(4-methylbenzyl)-6-styrylpyridazin-3(2H)-one (MBSP). The chemical structure of MBSP was characterized using spectroscopic techniques such as FT-IR, ¹H NMR, ¹³C NMR, UV-Vis, ESI-MS, and finally, the structure was confirmed by single X-ray diffraction studies. The DFT calculation was performed to compare the gas-phase geometry of the title compound to the solid-phase structure of the title compound. Furthermore, a comparative study between theoretical UV-Vis, IR, ¹H- and ¹³C NMR spectra of the studied compound and experimental ones have been carried out. The thermal behavior and stability of the compound were analyzed by using TGA and DTA techniques which revealed that the compound is thermostable up to its melting point. Finally, the in silico docking and ADME studies are performed to investigate whether MBSP is a potential therapeutic for COVID-19.

Design, synthesis and biological evaluation of novel 7-mercaptocoumarin derivatives as α(1)-adrenoceptor antagonists

Study on the pharmacophore model of α(1)-adrenoceptor (α(1)-AR) antagonists led to design a series of novel 7-mercaptocoumarin derivatives as α(1)-AR antagonists. All designed compounds have been synthesized and biologically evaluated. The results showed that most of them exhibited strong antagonistic activity. Especially compound 6 showed excellent activity, which was better than that of the reference compound prazosin. Structure-activity relationship studies revealed that small hydrophobic group at the terminal heterocyclic ring and ortho substituents on the phenyl ring of phenylpiperazine moiety were the essential structural factors for α(1)-AR antagonistic activity. The pharmacophore modeling studies further clarified their structural contributions to antagonistic activity and also demonstrated that 7-mercaptocoumarin moiety could be a useful scaffold for design of α(1)-AR antagonists.

Synthesis and complete assignment of the 1H and 13C NMR spectra of 6-substituted and 2,6-disubstituted pyridazin-3(2H)-ones

Several pyridazin-3(2H)-one derivatives were synthesized starting from alkyl furans using oxidation with singlet oxygen to give 4-methoxy or 4-hydroxybutenolides, key intermediates of the synthetic strategy followed. For all pyridazinones reported, a complete assignment of the (1)H and (13)C NMR spectra using one- and two-dimensional NMR spectroscopic methods, which included NOE, DEPT, COSY, HSQC and HMBC experiments, was accomplished. Correlations between the chemical shifts of the heterocyclic ring atoms and substituents at N-2 and C-6 were analyzed.

Rational design, synthesis, biological evaluation, homology and docking studies of coumarin derivatives as α1 -adrenoceptor antagonists

According to a three-point pharmacophore for some uro-selective α(1) -adrenoceptor (AR) antagonists, a novel class of coumarin (=2H-1-benzopyran-2-one) derivatives have been successfully designed and synthesized with high efficacies for α(1) -AR. These synthesized coumarin derivatives exhibited high efficacies towards α(1) -AR in in vitro pharmacological assays. Compared with prazosin (pK(i) value of 8.77), among those coumarins, tolylpiperazine-substituted derivatives, 7 and 8, have comparable pK(i) values of 8.81 and 8.77, respectively. The trend in efficacies of these coumarin derivatives towards α(1A) -adrenoceptor was further rationalized by intensive molecular docking. Our work demonstrated that the designed coumarin derivatives can inhibit α(1) -AR in vitro. These findings will provide a guide for further studies of the medical therapy of benign prostatic hyperplasia (BPH).

Synthesis and biological affinity of new imidazo- and indol-arylpiperazine derivatives: further validation of a pharmacophore model for alpha(1)-adrenoceptor antagonists

In the continuing search for selective alpha(1)-adrenoceptor (AR) antagonists, new alkoxyarylpiperazinylalkylpyridazinone derivatives were designed and synthesized. The new compounds were tested for their affinity toward alpha(1)-AR, alpha(2)-AR and 5-HT(1A) receptors. The ability of these compounds to inhibit the serotonin transporters (SERT) was also determined. The pharmacological data confirm that increasing the size of the ortho alkoxy substituent on the phenyl ring of the arylpiperazine moiety afforded compounds with enhanced affinity toward the alpha(1)-AR. The isopropoxy group, the largest group evaluated, led the best alpha(1)-AR affinity profile. In contrast, the compounds which have an amide group within of the o-alkoxy-phenylpiperazine fragment showed low affinity toward the receptors studied. Similar results were obtained when the amide group was present in the linker of the junction between the two major constituents of the molecule.

Synthesis, alpha 1-adrenoceptor antagonist activity, and SAR study of novel arylpiperazine derivatives of phenytoin

In the search for new antiarrhythmic agents, some active 2-methoxyphenylpiperazine derivatives of phenytoin were obtained as a chemical modification of compound AZ-99 (3-ethyl-1-[2-hydroxy-3-(4-phenylpiperazin-1-yl)-propyl]-2,4-dioxo-5,5-diphenylimidazolidine). These compounds possessed structural properties similar to those of alpha(1)-adrenoceptor antagonists. In the present study, the affinities of the 2-methoxyphenylpiperazine derivatives (1a-3a) for alpha(1)- and alpha(2)-adrenoceptors were evaluated using radioligand ([(3)H]prazosin, [(3)H]clonidine) binding assays. In the next step, a new series of phenylpiperazine derivatives of phenytoin (4a-16a) containing 2-methoxyphenyl-, 2-ethoxyphenyl-, 2-pyridyl- or 2-furoylpiperazine moiety, as well as, various ester or alkyl substituents at 3-position of hydantoin ring were synthesized. The newly synthesized compounds were tested for their affinity to alpha(1)- and alpha(2)-adrenoceptors. They have shown affinities for alpha(1)-adrenoceptors at nanomolar to submicromolar range. Some compounds were moderately selective ligands of alpha(1)-adrenoceptors. Selected compounds (3a-5a, 7a, 13a, 14a) were also evaluated for their alpha(1)-adrenoceptor antagonistic properties in functional bioassays. A SAR study indicated that the most active compounds contain 2-alkoxyphenylpiperazine moieties and methyl or 2-methylpropionate substituent at 3-N position in hydantoin. The exchange of 2-alkoxyphenyl moiety into 2-furoyl or 2-pyridyl group significantly decreased affinities for alpha(1)-adrenoceptors. Molecular modelling results obtained using conformational analysis CONFLEX and PM5 method for geometry optimization, allowed for comparison of the spatial properties of tested compounds with pharmacophore model created by Barbaro et al. for the ideal alpha(1)-adrenoceptor antagonist.

Functionalized heteroarylpyridazines and pyridazin-3(2H)-one derivatives via palladium-catalyzed cross-coupling methodology

A general method for the synthesis of functionalized pyridazinylboronic acids/esters is described involving a directed ortho metalation (DoM)--boronation protocol (Schemes 1 and 2). A comprehensive study of the reactivity of the C-B bond in palladium-catalyzed cross-couplings with aryl/heteroaryl halides is presented. Aryl-/heteroarylpyridazines are thereby obtained in synthetically viable yields (typically 40-75%) although in some cases competing protodeboronation has been observed. A series of pyridazin-3(2H)-one derivatives, including 4,6-diaryl/heteroaryl derivatives, have been obtained from the corresponding 3-methoxypyridazines in straightforward procedures (Schemes 3 and 4). Several X-ray crystal structures of aryl-/heteroarylpyridazines and derived pyridazin-3(2H)-one derivatives are reported. These multi-ring systems are of considerable interest in contemporary N-heterocyclic chemistry.

Synthesis and Pharmacological Evaluation of New 1-[3-(4-Arylpiperazin-1-yl)-2-hydroxypropyl]-pyrrolidin-2-one Derivatives with Anti-arrhythmic, Hypotensive, and α-Adrenolytic Activity

A series of novel arylpiperazines bearing a pyrrolidin-2-one fragment was synthesized and evaluated for the binding affinity of the alpha(1)- and alpha(2)-adrenoceptors (AR) and for the antiarrhythmic and hypotensive activities of the compounds. The most potent and selective compound 1-[2-hydroxy-3-[4-[(2-hydroxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-one 8 binds with pK(i) = 6.71 for alpha(1)-AR. Derivative 8 was also the most active in the prophylactic antiarrhythmic test in adrenaline-induced arrhythmia in anaesthetized rats. Its ED(50 )value equals 1.9 mg/kg (i.v.). Compounds with substituents such as a fluorine atom 4, a methyl 5, or a hydroxyl 8 group, or two substituents such as fluorine/chlorine atoms and methoxy groups in the phenyl ring, significantly decreased the systolic and diastolic pressure in normotensive anesthetized rats at a dosages of 5-10 mg/kg (i.v.). It was found that the presence of the piperazine ring and a hydroxy group in the second position of the propyl chain are critical structural features in determining the affinity of the compounds tested.

New 4-(4-methyl-phenyl)phthalazin-1(2H)-one derivatives and their effects on α1-receptors

Continuing our research aimed at obtaining new compounds with high affinity and selectivity toward alpha(1)-AR, a new series of arylpiperazine derivatives was designed, synthesized, and biologically tested. The new compounds 1-17 are characterized by a phenylphthalazin-1(2H)-one fragment connected through an alkyl chain to an arylpiperazine residue. The pharmacological profile of these compounds was evaluated for their affinity and selectivity toward alpha(1)-AR, alpha(2)-AR and toward 5HT(1A) serotoninergic receptor. A discussion on the structure-activity relationship (SAR) of these compounds is also reported.

A Genetic-Function-Approximation-Based QSAR Model for the Affinity of Arylpiperazines toward α1 Adrenoceptors

The genetic function approximation (GFA) algorithm has been used to derive a three-term QSAR equation able to correlate the structural properties of arylpiperazine derivatives with their affinity toward the alpha1 adrenoceptor (alpha1-AR). The number of rotatable bonds, the hydrogen-bond properties, and a variable belonging to a topological family of descriptors (chi) showed significant roles in the binding process toward alpha1-AR. The new model was also compared to a previous pharmacophore for alpha1-AR antagonists and a QSAR model for alpha2-AR antagonists with the aim of finding common or different key determinants influencing both affinity and selectivity toward alpha1- and alpha2-AR.

Synthesis of new piperazine–pyridazinone derivatives and their binding affinity toward α1-, α2-adrenergic and 5-HT1A serotoninergic receptors

We report the design and synthesis of a new class of piperazine-pyridazinone analogues. The arylpiperazine moiety, the length of the spacer, and the terminal molecular fragment were varied to evaluate their influence in determining the affinity of the new compounds toward the alpha1-adrenergic receptor (alpha1-AR), alpha2-adrenergic receptor (alpha2-AR), and the 5-HT1A serotoninergic receptor (5-HT1AR). Biological data showed that most of the compounds have an alpha1-AR affinity in the nanomolar or subnanomolar range, while affinity toward the other two receptors was lower in most cases. However, several of the tested compounds also showed very good (in the nanomolar range) or moderate affinity toward the 5-HT1AR subtype.

Synthesis and development of new 2-substituted 1-[3-(4-arylpiperazin-1-yl)propyl]-pyrrolidin-2-one derivatives with antiarrhythmic, hypotensive, and α-adrenolytic activity

A series of new 1-[3-(4-arylpiperazinyl-1-yl)-2-(N-alkylcarbamoyloxy)propyl]-pyrrolidin-2-one derivatives (4a-12a) were synthesised and tested for their electrocardiographic, antiarrhythmic and antihypertensive activity, as well as for the alpha1- and alpha2-adrenoceptor binding affinities. Of the newly synthesised derivatives, 1-{2-(N-2-methylethylcarbamoiloxy)-3-[4-(2-methoxyphenyl)piperazin-1-yl)]propyl}pyrrolidin-2-one dihydrochloride (10a) was the most active in prophylactic antiarrhythmic tests, its ED50 value equalling 2.7 mg kg(-1), and the therapeutic index being 75.2; moreover, compound 10a was also found to possess hypotensive activity. A preliminary molecular modelling study suggested that the selected alpha1-AR antagonist distances and angles between pharmacophoric features, estimated for the tested compounds, were in good agreement with the parameters evaluated for ligands.

Synthesis of 3-Arylpiperazinylalkylpyrrolo[3,2-d]pyrimidine-2,4-dione Derivatives as Novel, Potent, and Selective α1-Adrenoceptor Ligands

Novel compounds characterized by a pyrrolo[3,2-d]pyrimidine-2,4-dione (PPm) system connected through an alkyl chain to a phenylpiperazine (PPz) residue were designed as structural analogues of the alpha(1)-adrenoceptor (alpha(1)-AR) ligand RN5 (1). In this new series of derivatives an arylpyrrolo moiety has replaced the indole nucleus of RN5. Several structural modifications were performed on the PPm and PPz moieties and the connecting alkyl chain. These compounds were synthesized and tested in radioligand binding experiments where many of them showed interesting binding profiles. Some compounds, including 31, 34, and 36, displayed substantial alpha(1)-AR selectivity with respect to serotoninergic 5-HT(1A) and dopaminergic D(1) and D(2) receptors. Two different molecular modeling approaches (pharmacophoric mapping and quantitative structure-affinity relationship analysis) have been applied to rationalize, at a quantitative level, the relationships between affinity toward alpha(1)-ARs and the structure of the studied compounds. Several QSAR models have been reported and described, accounting for the influence of various molecular portions on such affinity data.

Variable selection and specification of robust QSAR models from multicollinear data: arylpiperazinyl derivatives with affinity and selectivity for ?2-adrenoceptors

Two QSAR models have been identified that predict the affinity and selectivity of arylpiperazinyl derivatives for alpha1 and alpha2 adrenoceptors (ARs). The models have been specified and validated using 108 compounds whose structures and inhibition constants (Ki) are available in the literature [Barbaro et al., J. Med. Chem., 44 (2001) 2118; Betti et al., J. Med. Chem., 45 (2002) 3603; Barbaro et al., Bioorg. Med. Chem., 10 (2002) 361; Betti et al., J. Med. Chem., 46 (2003) 3555]. One hundred and forty-seven predictors have been calculated using the Cerius 2 software available from Accelrys. This set of variables exhibited redundancy and severe multicollinearity, which had to be identified and removed as appropriate in order to obtain robust regression models free of inflated errors for the beta estimates - so-called bouncing betas. Those predictors that contained information relevant to the alpha2 response were identified on the basis of their pairwise linear correlations with affinity (-log Ki) for alpha2 adrenoceptors; the remaining variables were discarded. Subsequent variable selection made use of Factor Analysis (FA) and Unsupervised Variable Selection (UzFS). The data was divided into test and training sets using cluster analysis. These two sets were characterised by similar and consistent distributions of compounds in a high dimensional, but relevant predictor space. Multiple regression was then used to determine a subset of predictors from which to determine QSAR models for affinity to alpha2-ARs. Two multivariate procedures, Continuum Regression (the Portsmouth formulation) and Canonical Correlation Analysis (CCA), have been used to specify models for affinity and selectivity, respectively. Reasonable predictions were obtained using these in silico screening tools.

Design, synthesis, and α1-adrenoceptor binding properties of new arylpiperazine derivatives bearing a flavone nucleus as the terminal heterocyclic molecular portion

Following our research project aimed at obtaining new compounds with high affinity and selectivity toward alpha(1)-adrenoceptors (AR), a new class of piperazine derivatives was designed, synthesized and biologically tested. The new compounds 1-13 are characterized by a flavone system linked, through an ethoxy or propoxy spacer, to a phenyl- or pyridazinone-piperazine moiety. Biological data showed an interesting profile for the phenylpiperazine subclass found to have a nanomolar affinity toward alpha(1)-AR, and less pronounced affinity for alpha(2)-AR and the 5-HT(1A) serotoninergic receptor. A discussion on the structure-activity relationship (SAR) of such compounds is also reported, on the basis of the flavone substitution pattern, length and functionalization of the spacer, and disruption of the phenylpiperazine system.