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.     

Synthesis of 3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazoles,displaying combined 5-HT uptake inhibiting and alpha(2)-adrenoceptor antagonistic activities: a novel series of potential antidepressants

The synthesis of a series of novel 3-piperazinylmethyl-3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazoles as novel dual 5-HT reuptake inhibitors and alpha(2)-adrenoceptor antagonists is described. Their affinity at the three different human alpha(2)-adrenoceptor subtypes and the 5-HT transporter site is reported. The in vivo activity of the compounds was measured in two different assays: (1). inhibition of pCA-induced excitation, which evaluates the ability to block the central 5-HT transporter, and (2). inhibition of xylazine-induced loss of righting, which evaluates the ability to block central alpha(2)-adrenoceptors.     

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,pharmacology and pharmacokinetics of 3-(4-aryl-piperazin-1-ylalkyl)-uracils as uroselective alpha1A-antagonists

Predominance in the urethra and prostate of the alpha(1A)-adrenoceptor subtype, which is believed to be the receptor mediating noradrenaline induced smooth muscle contraction in these tissues, led to the preparation of alpha(1A)-selective antagonists to be tested as uroselective compounds for the treatment of benign prostatic hyperplasia. Thus, a number of selective alpha(1A)-adrenoceptor antagonists were synthesized and assayed in vitro for potency and selectivity. Dog pharmacokinetic parameters of 12 (RO700004) and its metabolite 40 (RO1104253) were established. The relative selectivity of intravenously administered 12, 40 and standard prazosin to inhibit hypogastric nerve stimulation-induced increases in intraurethral prostatic pressure versus phenylephrine-induced increases in diastolic blood pressure in anesthetized dogs was 76, 71 and 0.6, respectively.     

Synthesis and alpha(1)-adrenoceptor antagonist activity of derivatives and isosters of the furan portion of (+)-cyclazosin

alpha(1)-Adrenoceptor selective antagonists are crucial in investigating the role and biological functions of alpha(1)-adrenoceptor subtypes. We synthesized and studied the alpha(1)-adrenoceptor blocking properties of new molecules structurally related to the alpha(1B)-adrenoceptor selective antagonist (+)-cyclazosin, in an attempt to improve its receptor selectivity. In particular, we investigated the importance of substituents introduced at position 5 of the 2-furan moiety of (+)-cyclazosin and its replacement with classical isosteric rings. The 5-methylfuryl derivative (+)-3, [(+)-metcyclazosin], improved the pharmacological properties of the progenitor, displaying a competitive antagonism and an 11 fold increased selectivity for alpha(1B) over alpha(1A), while maintaining a similar selectivity for the alpha(1B)-adrenoceptor relative to the alpha(1D)-adrenoceptor. Compound (+)-3 may represent a useful tool for alpha(1B)-adrenoceptor characterization in functional studies.     

Antagonist like action of synthetic alpha 2-adrenoceptor agonists on contractile response to catecholamines in smooth muscle strips isolated from rainbow trout stomach (Salmo gairdneri)

1. The effects of some synthetic alpha 2-adrenoceptor agonists on the mechanical activity and on contractile responses to catecholamines were examined in smooth muscle strips isolated from rainbow trout stomach. 2. Contractile responses to noradrenaline and adrenaline in the rainbow trout stomach strips were due to alpha 2-adrenoceptor activation. 3. Clonidine, p-aminoclonidine, naphazoline and guanabenz caused no mechanical response but concentration-dependently inhibited the contractile responses to noradrenaline and adrenaline without affecting the responses to acetylcholine, carbachol, 5-hydroxytryptamine and methionine-enkephalin. The order of potency was naphazoline greater than p-aminoclonidine greater than clonidine greater than guanabenz. 4. It is suggested that in the smooth muscle preparation of the trout stomach, some synthetic compounds (clonidine, p-aminoclonidine, naphazoline and guanabenz), which act on mammalian preparations as alpha 2-adrenoceptor agonists, show an antinoradrenaline (-adrenaline) effect; those compounds can be classified as alpha 2-adrenoceptor antagonists.     

Structure--activity relationships among novel phenoxybenzamine-related beta-chloroethylamines

A series of beta-chloroethylamines 5--18, structurally related to the irreversible alpha(1)-adrenoceptor antagonist phenoxybenzamine [PB, N-benzyl-N-(2-chloroethyl)-N-(1-methyl-2-phenoxyethyl)amine hydrochloride, 1] and the competitive antagonist WB4101 [N-(2,3-dihydro-1,4-benzodioxin-2-ylmethyl)-N-[2-(2,6-dimethoxyphenoxy)ethyl]amine hydrochloride, 2], were synthesized and evaluated for their activity at alpha-adrenoceptors of the epididymal and the prostatic portion of young CD rat vas deferens. All compounds displayed irreversible antagonist activity. Most of them showed similar antagonism at both alpha(1)- and alpha(2)-adrenoceptors, whereas compounds 13 and 18, lacking substituents on both the phenoxy group and the oxyamino carbon chain, displayed a moderate alpha(1)-adrenoceptor selectivity (10--35 times), which was comparable to that of PB. Compounds 14 and 15, belonging to the benzyl series and bearing, respectively, a 2-ethoxyphenoxy and a 2-i-propoxyphenoxy moiety, were the most potent alpha(1)-adrenoceptor antagonists with an affinity value similar to that of PB (pIC(50) values of 7.17 and 7.06 versus 7.27). Interestingly, several compounds were able to distinguish two alpha(1)-adrenoceptor subtypes in the epididymal tissue, as revealed by the discontinuity of their inhibition curves. A mean ratio of 24:76 for these alpha(1)-adrenoceptors was determined from compounds 8--10, 12, and 15--17. Furthermore, compounds 9, 10, 12, 16a, and 16b showed higher affinity towards the minor population of receptors, whereas compounds 8, 15, and 17 preferentially inhibited the major population of alpha(1)-adrenoceptors. In addition, selected pharmacological experiments demonstrated the complementary antagonism of the two series of compounds and their different, preferential affinity for one of the two alpha(1)-adrenoceptor subtypes. In conclusion, we found beta-chloroethylamines that demonstrate a multiplicity of alpha(1)-adrenoceptors in the epididymal portion of young CD rat vas deferens and, as a consequence, they are possible useful tools for alpha(1)-adrenoceptor characterization.     

A Comparison of Varying alpha-Blockers and Other Pharmacotherapy Options for Lower Urinary Tract Symptoms

alpha(1)-Adrenoceptor antagonists are now well established as the most common treatment for lower urinary tract symptoms (LUTS) suggestive of bladder outflow obstruction associated with benign prostatic hyperplasia. Both alpha(1)-adrenoceptor antagonists and 5alpha-reductase inhibitors are accepted treatments for LUTS, but with finasteride this applies only to patients with clinically enlarged prostates, whereas alpha(1)-adrenoceptor antagonists are considered to be appropriate treatment for all patients, irrespective of prostate size. Systematic analyses of placebo-controlled studies show that commonly used alpha(1)-blockers are significantly superior to placebo in improving urinary flow and reducing symptoms. Efficacy of alpha-blockers appears to be well maintained over time, and there is no evidence of tolerance or tachyphylaxis to alpha(1)-blockade after 6-12 months' usage. Direct comparative trials show that, in the short term, alpha(1)-adrenoceptor antagonists are more effective than finasteride in reducing symptom score. For alpha(1)-adrenoceptor antagonists, the most commonly reported adverse effects are dizziness, asthenia, postural hypotension, and syncope. Alfuzosin has a more pronounced effect on blood pressure than does tamsulosin, especially in elderly patients. Tamsulosin is well tolerated and has minimal effects on blood pressure; tamsulosin 0.4 mg has the lowest potential to reduce blood pressure and causes less symptomatic orthostatic hypotension than terazosin.     

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 3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazoles, displaying combined 5-HT uptake inhibiting and alpha2-adrenoceptor antagonistic activities. Part 2: Further exploration on the cinnamyl moiety

In our previous paper we have described the synthesis of a series of 3-piperazinylmethyl-3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazoles, as novel dual 5-HT reuptake inhibitors and alpha2-adrenoceptor antagonists. That investigation led to the identification of the cinnamyl fragment as the most suitable moiety for combined activity. This paper outlines a further optimisation programme, focused on the exploration of the aromatic ring present on the cinnamyl moiety of compounds 1, 2 and 3.     

Synthesis of 7-amino-3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazole derivatives displaying combined alpha2-adrenoceptor antagonistic and 5-HT reuptake inhibiting activities

Following a program searching for dual 5-HT reuptake inhibitors and alpha(2)-adrenoceptor antagonists started at Johnson & Johnson Pharmaceutical Research & Development, we now report on the synthesis of a series of 7-amino-3a,4-dihydro-3H-[1]benzopyrano[4,3-c]isoxazole derivatives, some of which proved to be the most potent alpha(2)-adrenoceptor blockers within this chemical class of tricyclic isoxazolines, while keeping potent 5-HT reuptake inhibiting activity.     

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.     

Exploring the active site of phenylethanolamine N-methyltransferase with 3-hydroxyethyl- and 3-hydroxypropyl-7-substituted-1,2,3,4-tetrahydroisoquinolines

3-Hydroxyethyl- and 3-hydroxypropyl-7-substituted-tetrahydroisoquinolines (9, 10, 16, and 17) were synthesized and evaluated for their phenylethanolamine N-methyltransferase (PNMT) inhibitory potency and affinity for the alpha(2)-adrenoceptor. Although alpha(2)-adrenoceptor affinity decreased for these compounds, selectivity was not gained over the parent 3-hydroxymethyl compounds (1, 2) due to a loss in PNMT inhibitory potency.     

Theoretical proton affinities of alpha1 adrenoceptor ligands

A systematic study has been performed of the proton affinity of a large family of agonists and antagonists of the alpha1-adrenoceptor at the B3LYP/6-31G* level of theory. After a conformational search, all the N atoms were considered as protonation sites and protonation energy values were determined. The inclusion of solvation by means of the Onsager model yielded stabilization in the proton affinity values obtained. In addition, a good correlation was found between the proton affinity values corresponding to the first protonation in gas phase of some of the compounds and their corresponding experimental affinity constants K(i) for the alpha1A adrenergic receptor.     

Alpha 2-adrenoceptor antagonists block the stimulant effects of cocaine in mice.

In the present study we have investigated the effects of the alpha 2-adrenoceptor antagonist idazoxan and its 2-ethoxy derivative RX811059 on the locomotor activity induced by cocaine in mice. The stimulant effects of cocaine (15 mg/kg i.p.) were significantly antagonised by idazoxan (3 mg/kg i.p.) and RX811059 (1 mg/kg i.p.) and also initially suppressed by idazoxan (1 mg/kg i.p.) and RX811059 (0.3 mg/kg i.p.). The alpha 2-adrenoceptor antagonists had no effect on locomotion when given alone. These results suggest that noradrenergic mechanisms may play a role in the stimulant effects of cocaine and that alpha 2-adrenoceptor antagonists like idazoxan may be of some benefit in the clinical management of cocaine abuse.     

Cell surface delivery and structural re-organization by pharmacological chaperones of an oligomerization-defective alpha(1b)-adrenoceptor mutant demonstrates membrane targeting of GPCR oligomers

Many G-protein-coupled receptors, including the alpha(1b)-adrenoceptor, form homo-dimers or oligomers. Mutation of hydrophobic residues in transmembrane domains I and IV alters the organization of the alpha(1b)-adrenoceptor oligomer, with transmembrane domain IV playing a critical role. These mutations also result in endoplasmic reticulum trapping of the receptor. Following stable expression of this alpha(1b)-adrenoceptor mutant, cell surface delivery, receptor function and structural organization were recovered by treatment with a range of alpha(1b)-adrenoceptor antagonists that acted at the level of the endoplasmic reticulum. This was accompanied by maturation of the mutant receptor to a terminally N-glycosylated form, and only this mature form was trafficked to the cell surface. Co-expression of the mutant receptor with an otherwise wild-type form of the alpha(1b)-adrenoceptor that is unable to bind ligands resulted in this wild-type variant also being retained in the endoplasmic reticulum. Ligand-induced cell surface delivery of the mutant alpha(1b)-adrenoceptor now allowed co-recovery to the plasma membrane of the ligand-binding-deficient mutant. These results demonstrate that interactions between alpha(1b)-adrenoceptor monomers occur at an early stage in protein synthesis, that ligands of the alpha(1b)-adrenoceptor can act as pharmacological chaperones to allow a structurally compromised form of the receptor to pass cellular quality control, that the mutated receptor is not inherently deficient in function and that an oligomeric assembly of ligand-binding-competent and -incompetent forms of the alpha(1b)-adrenoceptor can be trafficked to the cell surface by binding of a ligand to only one component of the receptor oligomer.     

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.     

Differential effect of pertussis toxin on the affinity state for agonists of renal alpha 1- and alpha 2- adrenoceptors

The effect of pertussis toxin treatment on the guanine nucleotide-induced modulation of the affinity of renal alpha 1- and alpha 2-adrenergic receptors was investigated. Pretreatment of rats with pertussis toxin did not induce any change in the number of or affinity for antagonists of alpha 1- or alpha 2-receptors studied using [3H]prazosin and [3H]yohimbine, respectively. Guanyl-5'-yl imidodiphosphate induced an "up-shift" in the number of alpha 2-adrenergic receptors; this up-shift was not observed for alpha 1-adrenergic receptors. Pertussis toxin treatment decreased the affinity of epinephrine for the [3H]yohimbine-binding sites and reduced the ability of guanine nucleotides to modulate alpha 2-adrenoceptor agonist affinity. The regulation by guanine nucleotides of alpha 1-adrenoceptor affinity for agonists was not altered. These results suggest that the modulation of alpha 1- and alpha 2-adrenoceptors by guanine nucleotides is probably exerted through different molecular entities.     

3-Arylpiperazinylethyl-1H-pyrrolo[2,3-d]pyrimidine-2,4(3H,7H)-dione derivatives as novel, high-affinity and selective alpha(1)-adrenoceptor ligands

The discovery of a new series of selective and high-affinity alpha(1)-adrenoceptor (alpha(1)-AR) ligands, characterized by a 1H-pyrrolo[2,3-d]-pyrimidine-2,4(3H,7H)-dione system, is described in this paper. Some synthesized compounds, including 20, 22, and 30, displayed affinity in the nanomolar range for alpha(1)-ARs and substantial selectivity with respect to 5-HT(1A) and dopaminergic D(1) and D(2) receptors. Functional assays, performed on selected derivatives, showed antagonistic properties.