Structure-activity relationships in 1,4-benzodioxan-related compounds. 6. Role of the dioxane unit on selectivity for alpha(1)-adrenoreceptor subtypes

Multitarget 1,4-Dioxane Compounds Combining Favorable D2-like and 5-HT1A Receptor Interactions with Potential for the Treatment of Parkinson's Disease or Schizophrenia

The effect of methoxy and hydroxy substitutions in different positions of the phenoxy moiety of the N-((6,6-diphenyl-1,4-dioxan-2-yl)methyl)-2-phenoxyethan-1-amine scaffold on the affinity/activity for D₂-like, 5-HT_1A, and α₁-adrenoceptor subtypes was evaluated. Multitarget compounds with suitable combinations of dopaminergic and serotoninergic profiles were discovered. In particular, the 2-methoxy derivative 3 showed a multitarget combination of 5-HT_1A/D₄ agonism and D₂/D₃/5-HT_2A antagonism, which may be a favorable profile for the treatment of schizophrenia. Interestingly, the 3-hydroxy derivative 8 behaved as a partial agonist at D₂ and as a potent full agonist at D₃ and D₄ subtypes. In addition to its potent 5-HT_1A receptor agonism, such a dopaminergic profile makes 8 a potential multitarget compound for the treatment of Parkinson's disease (PD). Indeed, the activation of 5-HT_1A receptors might be helpful in reducing dyskinetic side effects associated with dopaminergic stimulation.

Affinity and activity profiling of unichiral 8-substituted 1,4-benzodioxane analogues of WB4101 reveals a potent and selective α1B-adrenoceptor antagonist

Unichiral 8-substituted analogues of 2-[(2-(2,6-dimethoxyphenoxy)ethyl)aminomethyl]-1,4-benzodioxane (WB4101) were synthesized and tested for binding affinity at cloned human α(1a)-, α(1b)-and α(1d)-adrenoreceptor (α(1a)-, α(1b)-and α(1d)-AR) and at native rat 5-HT(1A) receptor and for antagonist affinity at α(1A)-, α(1B)-and α(1D)-AR and at α(2A/D)-AR. Among the selected 8-substituents, namely fluorine, chlorine, methoxyl and hydroxyl, only the last caused significant decrease of α(1) binding affinity in comparison with the lead compound. Functional tests on the S isomers confirmed the detrimental effect of OH positioned in proximity to benzodioxane O(1). For the other three substituents (F, Cl, OMe), the α(1A) and the α(1D) antagonist affinities were generally lower than the α(1a) and α(1d) binding affinities, but not the α(1B) antagonist affinity, which was similar and sensibly higher compared to α(1b) binding affinity in the case of F and OMe respectively. This trend confers significant α(1B)-AR selectivity, in particular, to the 8-methoxy analogue of (S)-WB4101, a new potent (pA(2) 9.58) α(1B)-AR antagonist. The S enantiomers of all the tested compounds were proved to act as α(1)-AR inverse agonists in a vascular model.

Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA) studies on α(1A)-adrenergic receptor antagonists based on pharmacophore molecular alignment

The α_1A-adrenergic receptor (α_1A-AR) antagonist is useful in treating benign prostatic hyperplasia, lower urinary tract symptoms, and cardiac arrhythmia. Three-dimensional quantitative structure-activity relationship (3D-QSAR) studies were performed on a set of α_1A-AR antagonists of N-aryl and N-nitrogen class. Statistically significant models constructed from comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) were established based on a training set of 32 ligands using pharmacophore-based molecular alignment. The leave-oneout cross-validation correlation coefficients were q²_CoMFA = 0.840 and q²_CoMSIA = 0.840. The high correlation between the cross-validated/predicted and experimental activities of a test set of 12 ligands revealed that the CoMFA and CoMSIA models were robust (r²_pred/CoMFA = 0.694; r²_pred/CoMSIA = 0.671). The generated models suggested that electrostatic, hydrophobic, and hydrogen bonding interactions play important roles between ligands and receptors in the active site. Our study serves as a guide for further experimental investigations on the synthesis of new compounds. Structural modifications based on the present 3D-QSAR results may lead to the discovery of other α_1A-AR antagonists.

Unexpected tandem ylide annulation reaction for controllable synthesis of 2H-chromenes and 4H-chromenes

[reaction: see text] An unexpected tetrahydrothiophene-catalyzed ylide annulation reaction, via tandem Michael addition/elimination/substitution, for the controllable synthesis of 2H-chromenes and 4H-chromenes has been developed.

QSAR study for a novel series of ortho disubstituted phenoxy analogues of α1-adrenoceptor antagonist WB4101

On the basis of the affinities at the alpha1a-, alpha1b- and alpha1d-adrenoceptors and the 5-HT1A receptor of a previous series of sixteen 2-[(2-phenoxyethyl)aminomethyl]-1,4-benzodioxanes ortho monosubstituted at the phenoxy moiety, a number of ortho disubstituted analogues were designed, synthesized in both the enantiomeric forms and tested in binding assays on the same receptors. The affinity values of the new compounds 1-11 were compared with those of the enantiomers of the 2,6-dimethoxyphenoxy analogue, the well-known alpha1 antagonist WB4101, and of the ortho monosubstituted derivatives, suggesting some distinctive aspects of the interaction of the phenoxy moiety, in particular with the alpha1a-AR and the 5-HT1A receptor, of the monosubstituted and the disubstituted compounds. A classical quantitative structure-activity relationship (Hansch) analysis was applied to the whole set of the S enantiomers of the ortho mono- and disubstituted WB4101 analogues (26 compounds), finding a very good correlation for the alpha1a affinity. For this latter, a significant parabolic relationship was also found with the volume of the two ortho substituents. Diametrically opposite, the same relationships for the 5-HT1A exhibit low or insignificant correlation coefficients.

GPCR antitarget modeling: pharmacophore models for biogenic amine binding GPCRs to avoid GPCR-mediated side effects

G protein-coupled receptors (GPCRs) form a large protein family that plays an important role in many physiological and pathophysiological processes. However, the central role that the biogenic amine binding GPCRs and their ligands play in cell signaling poses a risk in new drug candidates that reveal side affinities towards these receptor sites. These candidates have the potential to interfere with the physiological signaling processes and to cause undesired effects in preclinical or clinical studies. Here, we present 3D cross-chemotype pharmacophore models for three biogenic amine antitargets: the alpha(1A) adrenergic, the 5-HT(2A) serotonin, and the D2 dopamine receptors. These pharmacophores describe the key chemical features present within these biogenic amine antagonists and rationalize the biogenic amine side affinities found for numerous new drug candidates. First applications of the alpha(1A) adrenergic receptor model reveal that these in silico tools can be used to guide the chemical optimization towards development candidates with fewer alpha(1A)-mediated side effects (for example, orthostatic hypotension) and, thus, with an improved clinical safety profile.

QSAR study for a novel series of ortho monosubstituted phenoxy analogues of α1-adrenoceptor antagonist WB4101

A number of (S)- and (R)-2-[(2-phenoxyethyl)aminomethyl]-1,4-benzodioxanes unsubstituted or ortho monosubstituted at the phenoxy moiety were synthesized and tested in binding assays on the alpha(1a)-AR, alpha(1b)-AR, alpha(1d)-AR and the 5-HT(1A) receptor. The affinity values of the new compounds 1-16 were compared with those of the enantiomers of the 2,6-dimethoxyphenoxy analogue, the well-known alpha(1) antagonist WB4101, finding that the unsubstituted derivative (S)-1 and the o-methyl, the o-t-butyl, the o-fluoro and the o-methoxy derivatives, (S)-2, (S)-4, (S)-8 and (S)-16, respectively, display a significantly specific 5-HT(1A) affinity, very close, with the exception of (S)-4, to the almost nanomolar one of (S)-WB4101. Otherwise, sensible affinity decreases were recorded for the three alpha(1)-AR subtypes. A classical quantitative structure-activity relationship (Hansch) analysis was successfully applied to compounds (S)-1 to (S)-16 and (S)-WB4101 to rationalize such binding data.

Structure–affinity studies for a novel series of homochiral naphtho and tetrahydronaphtho analogues of α1 antagonist WB-4101

A number of enantiomeric pairs of naphthodioxane, tetrahydronaphthodioxane and naphthoxy analogues of WB-4101 (1) were designed and synthesized in order to improve the selectivity profile of the parent compound, hopefully in favour of the alpha(1a)-AR with respect to the other two alpha(1) subtypes and the 5-HT(1A) receptor. The new compounds 2-8 and, in addition, the two enantiomers of 1 were tested in binding assays on the alpha(1a)-AR, alpha(1b)-AR, alpha(1d)-AR, and the 5-HT(1A) receptor. Two of them, namely the naphtho- and tetrahydronaphthodioxane derivatives (S)-2 and (S)-3, showed lower, but significantly more specific alpha(1a) affinity than (S)-1, while the two enantiomers of the 2-methoxy-1-naphthoxy analogue 6 maintained most of the very high alpha(1a) affinity of (S)-1 and its alpha(1a) versus alpha(1b) selectivity slightly increasing the alpha(1a)/alpha(1d) and alpha(1a)/5HT(1A) affinity ratios. The SAR data were evaluated in the light of known alpha(1) subtype pharmacophores and of the alpha(1a)-AR binding mode of WB-4101 resultant from literature mutagenesis studies disclosing some interesting consonances with these models.

Synthesis and biological activity of new 1,4-benzodioxan-arylpiperazine derivatives. Further validation of a pharmacophore model for alpha(1)-adrenoceptor antagonists

A series of WB4101 (1)-related benzodioxanes (2-17) have been synthesized by replacing the phenoxyethyl moiety of 1 with a N-alkyl piperazine bearing a cyclic substituent (a substituted or unsubstituted phenyl group, a pyridine or pyridazinone ring, a furoyl moiety) at the second nitrogen atom. The binding profile of these compounds has been assessed by radioligand receptor binding assay at alpha(1)- and alpha(2)-adrenoceptors, in comparison to prazosin and rauwolscine, respectively. Moreover, structure-activity relationships have been derived for compounds 2-17 based on their fitting to a pharmacophore model for alpha(1)-adrenoceptor antagonists recently proposed by our research group. In a parallel way, the same compounds have been used to further test the predictive power and statistical significance of the model itself. The accuracy of the results obtained also in this case revealed the robustness of the calculated pharmacophore model and led to the identification of the molecular structural moieties which are thought to contribute to the biological activity.

New aromatic iminoimidazolidine derivatives as alpha1-adrenoceptor antagonists: a novel synthetic approach and pharmacological activity

The design, synthesis and alpha1-adrenoceptor antagonism of a series of bis-imidazoline (1a, 2a, 3a and 4a) and bis-guanidine (1b, 2b, 3b and 4b) diphenyl derivatives are reported. All of these compounds fulfill the conditions of the most recent pharmacophore proposed for alpha1-adrenoceptors and found in the literature. Besides, a novel synthetic approach to the preparation of 2-(arylimino)imidazolidine derivatives is described. All the tested compounds, except the bis-guanidinium derivative 3b, inhibit the contractile responses induced by noradrenaline in aortic rings of rat and rabbit in a dose-dependent manner. Our results indicate that, even though some discrepancies are observed in terms of the alpha1 subtype targeted by this new family of compounds, they show an interesting profile as antagonists of alpha1-adrenoceptors and a new prototype, compound 1a, has been found deserving further development.

Synthesis of 2-substituted-2,3- dihydro-1,4-dioxino[2,3-b]pyridine derivatives

[reaction--see text] A variety of 2-substituted-2,3-dihydro-1,4-dioxino[2,3-b]pyridines B have been synthesized from the readily available 2-nitro-3-oxiranylmethoxypyridine 1 via a Smiles rearrangement. We demonstrate how variations of reaction conditions affect the product distribution of A and B.