Design and synthesis of new tetrazolyl- and carboxy-biphenylylmethyl-quinazolin-4-one derivatives as angiotensin II AT1 receptor antagonists

A series of novel quinazolin-4-ones was designed and their molecular modeling simulation fitting to a new HipHop 3D pharmacophore model using CATALYST was examined. Several compounds showed significant high simulation fit values. The designed compounds were synthesized and eight of them were biologically evaluated in vitro using an AT1 receptor binding assay, where compound XX competed weakly against radiolabeled Sar1Ile8-angiotensin II (Ang II) binding, compounds XIV and XXII showed moderate competition, and compound XXV showed almost equal ability to displace radiolabeled Sar1Ile8-Ang II binding to AT1 receptors as losartan. In vivo biological evaluation study of compounds XIV, XXII, and XXV on both normotensive and hypertensive rats revealed that compound XXV demonstrated higher hypotensive and antihypertensive activity than the reference compound losartan. To obtain a highly active compound from a candidate set of only eight tested compounds illustrates the power and utility of our pharmacophore model.     

Synthesis, biological evaluation, and pharmacophore generation of new pyridazinone derivatives with affinity toward alpha(1)- and alpha(2)-adrenoceptors

A series of new pyridazin-3(2H)-one derivatives (3 and 4) were evaluated for their in vitro affinity toward both alpha(1)- and alpha(2)-adrenoceptors by radioligand receptor binding assays. All target compounds showed good affinities for the alpha(1)-adrenoceptor, with K(i) values in the low nanomolar range. The polymethylene chain constituting the spacer between the furoylpiperazinyl pyridazinone and the arylpiperazine moiety was shown to influence the affinity and selectivity of these compounds. Particularly, a gradual increase in affinity was observed by lengthening the polymethylene chain up to a maximum of seven carbon atoms. In addition, compound 3k, characterized by a very interesting alpha(1)-AR affinity (1.9 nM), was also shown to be a highly selective alpha(1)-AR antagonist, the affinity ratio for alpha(2)- and alpha(1)-adrenoceptors being 274. To gain insight into the structural features required for alpha(1) antagonist activity, the pyridazinone derivatives were submitted to a pharmacophore generation procedure using the program Catalyst. The resulting pharmacophore model showed high correlation and predictive power. It also rationalized the relationships between structural properties and biological data of, and external to, the pyridazinone class.     

Phenylpiperazinylalkylamino substituted pyridazinones as potent alpha(1) adrenoceptor antagonists.

QSAR models have been used for designing a series of compounds characterized by a N-phenylpiperazinylalkylamino moiety linked to substituted pyridazinones, which have been synthesized. Measurements of the binding affinities of the new compounds toward the alpha(1a)-, alpha(1b)-, and alpha(1d)-AR cloned subtypes as well as the 5-HT(1A) receptor have been done validating, at least in part, the estimations of the theoretical models. This study provides insight into the structure activity relationships of the alpha(1)-ARs ligands and their alpha(1)-AR/5-HT(1A) selectivity.     

Recent advances in alpha1-adrenoreceptor antagonists as pharmacological tools and therapeutic agents

Native alpha(1)-adrenoreceptors (ARs) appear to exist as three different subtypes encoded by three genes, alpha(1A/1a), alpha(1B/1b), and alpha(1D/1d). Historically, the discovery of agents selective for each of the three alpha(1)-AR subtypes has been an active area of medicinal chemistry research because of the wide number of possible therapeutic applications. Initially introduced for the management of hypertension, alpha(1)-AR antagonists have, in fact, become increasingly common in the treatment of benign prostatic hyperplasia (BPH), and are effective therapeutic tools, when characterized by an appropriate uroselective profile. The majority of these derivatives display a competitive mechanism of action and belong to a variety of structural classes, but this review is focused on compounds belonging to the quinazoline, benzodioxane, arylpiperazine, and 1,4-dihydropyridine classes.     

Guanidine and 2-aminoimidazoline aromatic derivatives as alpha(2)-adrenoceptor antagonists, 1: toward new antidepressants with heteroatomic linkers

The efficient preparation and pharmacological characterization of different families of (bis)guanidine and (bis)2-aminoimidazoline derivatives ("twin" and "half" molecules) as potential alpha(2)-adrenoceptor antagonists for the treatment of depression is presented. The affinity toward the alpha(2)-adrenoceptor of all the compounds prepared was measured in vitro in human brain tissue. Additionally, the activity as agonist or antagonist of those compounds with a pK(i) larger than 7 was determined in functional [(35)S]GTPgammaS binding assays in human brain tissue. Finally, the activity of the most promising compounds was confirmed by means of in vivo microdialysis experiments in rats. Compounds 1, 2b, 3b, 12b, 13b, 17b, 18b, 22b, 25b, 26b, 28b, and 30 showed a good affinity toward the alpha(2)-ARs. In general, the 2-aminoimidazoline derivatives displayed higher affinities than their guanidine analogues. Finally and most importantly, compounds 18b and 26b showed antagonistic properties over alpha(2)-ARs not only in vitro [(35)S]GTPgammaS binding but also in vivo microdialysis experiments. Moreover, both compounds have shown to be able to cross the blood-brain barrier and, therefore, they can be considered as potential antidepressants.     

Design and synthesis of novel alpha(1)(a) adrenoceptor-selective antagonists. 2. Approaches to eliminate opioid agonist metabolites via modification of linker and 4-methoxycarbonyl-4-phenylpiperidine moiety

We have previously described compound 1a as a high-affinity subtype selective alpha(1a) antagonist. In vitro and in vivo evaluation of compound 1a showed its major metabolite to be a mu-opioid agonist, 4-methoxycarbonyl-4-phenylpiperidine (3). Several dihydropyrimidinone analogues were synthesized with the goal of either minimizing the formation of 3 by modification of the linker or finding alternative piperidine moieties which when cleaved as a consequence of metabolism would not give rise to mu-opioid activity. Modification of the linker gave several compounds with good alpha(1a) binding affinity (K(i) = < 1 nM) and selectivity (>300-fold over alpha(1b) and alpha(1d)). In vitro analysis in the microsomal assay revealed these modifications did not significantly affect N-dealkylation and the formation of the piperidine 3. The second approach, however, yielded several piperidine replacements for 3, which did not show significant mu-opioid activity. Several of these compounds maintained good affinity at the alpha(1a) adrenoceptor and selectivity over alpha(1b) and alpha(1d). For example, the piperidine fragments of (+)-73 and (+)-83, viz. 4-cyano-4-phenylpiperidine and 4-methyl-4-phenylpiperidine, were essentially inactive at the mu-opioid receptor (IC(50) > 30 microM vs 3 microM for 3). Compounds (+)-73 and (+)-83 were subjected to detailed in vitro and in vivo characterization. Both these compounds, in addition to their excellent selectivity (>880-fold) over alpha(1b) and alpha(1d), also showed good selectivity over several other recombinant human G-protein coupled receptors. Compounds (+)-73 and (+)-83 showed good functional potency in isolated human prostate tissues, with K(b)s comparable to their in vitro alpha(1a) binding data. In addition, compound (+)-73 also exhibited good uroselectivity (DBP K(b)/IUP K(b) > 20-fold) in the in vivo experiments in dogs, similar to 1a.     

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

Alpha(1)-adrenoceptor antagonists. 4. Pharmacophore-based design,synthesis, and biological evaluation of new imidazo-, benzimidazo-, and indoloarylpiperazine derivatives

As a part of a program aimed at discovering compounds endowed with alpha(1)-adrenoceptor (AR) blocking properties, in this paper we describe the synthesis and biological characterization of the compounds designed to fully match a three-dimensional pharmacophore model for alpha(1)-AR antagonists previously developed by our research group. Accordingly, the structure of trazodone (1), identified during a database search performed by using the model as a 3D query, was chosen as the starting point for this study and modified following suggestions derived from a literature survey. In particular, the triazolopyridine moiety of trazodone was replaced with different heteroaromatic rings (such as imidazole, benzimidazole, and indole), and a pyridazin-3(2H)-one moiety was inserted into the scaffold of the new compounds to increase the overall length of the molecules and to allow for a complete fit into all the pharmacophore features. Our aim was also to study the influence of the position of both the chloro and the methoxy groups on the piperazine phenyl ring, as well as the effect of the lengthening or shortening of the polymethylene spacer linking the phenylpiperazine moiety to the terminal heterocyclic portion. Compounds obtained by such structural optimization share a 6-(imidazol-1-yl)-, 6-(benzimidazol-1-yl)-, or 6-(indol-1-yl)pyridazin-3(2H)-one as a common structural feature that represents an element of novelty in the SAR of arylpiperazine compounds acting toward alpha(1)-AR. Biological evaluation by radioligand receptor binding assays toward alpha(1)-AR, alpha(2)-AR, and 5-HT(1A) serotoninergic receptors indicated compounds characterized by very good alpha(1)-AR affinity and selectivity. Very interestingly, chemical features (such as the o-methoxyphenylpiperazinyl moiety and an alkyl spacer of three or four methylene units) that generally do not allow for 5-HT(1A)/alpha(1) selectivity led to compounds 2c and 6c with a 5-HT(1A)/alpha(1) ratio of 286 and 281, respectively. Finally, compounds with the best alpha(1)-AR affinity profile (2c, 5f, and 6c) were demonstrated to be alpha(1)-AR antagonists.     

Study of the in vivo and in vitro cardiovascular effects of four new analogues of ketanserin: implication of 5-HT2A and alpha1 adrenergic antagonism in their hypotensive effect

The in vivo and in vitro cardiovascular effects of the novel 5-HT2A/alpha1/H1 antagonist ketanserin analogues QF 0303B, QF 0307B, QF 0311B, QF 0313B were studied in anaesthetized normotensive rats (ANR) and in isolated rubbed rat aorta (IRRA). In ANR, 0.2 mg x kg(-1) i.v. of each compound produced a rapid, remarkable but short-lasting fall in mean arterial blood pressure (MAP) accompanied by bradycardia. All compounds significantly modified the pressor effects induced by 5-hydroxytryptamine (5-HT) and noradrenaline (NA). In IRRA, the compounds inhibited NA- and 5-HT-induced contractions in a competitive fashion. Furthermore, the analogues displayed lower H1-antagonist activity than ketanserin. Compounds tested showed low 5-HT2B affinity and no activity at muscarinic, nicotinic, or 5-HT3 receptors, nor any marked ability to produce smooth muscle relaxation via calcium entry blockade. There is a significant correlation between hypotension reached and inhibition of the 5-HT-induced pressor responses (but not for NA). A certain degree of correlation was observed between hypotensive effect endurance vs. alpha1-adrenoceptor blockade (but not for serotonin). These results indicate that in this series the brief hypotensive activity in ANR is attributed to a 5-HT1A receptor blockade and the duration of the effect is better attributed to an alpha1 adrenoceptor blockade.     

WB4101-related compounds: new, subtype-selective alpha1-adrenoreceptor antagonists (or inverse agonists?)

Our previous structure-affinity relationship study had considered the enantiomers of the naphthodioxane, tetrahydronaphthodioxane, and 2-methoxy-1-naphthoxy analogues (compounds 1, 3, and 2, respectively) of 2-(2,6-dimethoxyphenoxyethylaminomethyl)-1,4-benzodioxane, the well-known alpha1-adrenoceptor (alpha1-AR) antagonist WB4101, showing that such modifications significantly modulate the affinity and selectivity profile for alpha1-AR subtypes and 5-HT1A receptor. Here, we extend investigations to antagonist activity enclosing new enantiomeric pairs, namely those of the methoxytetrahydronaphthoxy and methoxybiphenyloxy WB4101 analogues (4 and 5-7, respectively) and of a double-modified WB4101 derivative (8) resulting from hybridization between 2 and 3. We found that (S)-2 is a very potent (pA2 10.68) and moderately selective alpha1D-AR antagonist and the hybrid (S)-8 is a potent (pA2 7.98) and highly selective alpha1A-AR antagonist. Both of these compounds and (S)-WB4101 seem to act as inverse agonists in a vascular model. The results, which generally validate the logic we followed in designing these eight compounds, are acceptably rationalized by comparative SAR analysis of binding and functional affinities.     

8-NH2-boldine, an antagonist of alpha1A and alpha1B adrenoceptors without affinity for the alpha1D subtype: structural requirements for aporphines at alpha1-adrenoceptor subtypes

Structure-activity analysis of 21 aporphine derivatives was performed by examining their affinities for cloned human alpha (1A), alpha (1B) and alpha (1D) adrenoceptors (AR) using membranes prepared from rat-1 fibroblasts stably expressing each alpha (1)-AR subtype. All the compounds tested competed for [ (125)I]-HEAT binding with steep and monophasic curves. The most interesting compound was 8-NH (2)-boldine, which retains the selective affinity for alpha(1A)-AR (pKi = 6.37 +/- 0.21) vs. alpha(1B)-AR (pKi = 5.53 +/- 0.11) exhibited by 1,2,9,10-tetraoxygenated aporphines, but shows low affinity for alpha(1D)-AR (pKi < 2.5). Binding studies on native adrenoceptors present in rat cerebral cortex confirms the results obtained for human cloned alpha (1)-AR subtypes. The compounds selective for the alpha (1A) subtype discriminate two binding sites in rat cerebral cortex confirming a mixed population of alpha (1A)- and alpha (1B)-AR in this tissue. All compounds are more selective as inhibitors of [ (3)H]-prazosin binding than of [ (3)H]-diltiazem binding to rat cerebral cortical membranes. A close relationship was found between affinities obtained for cloned alpha (1A)-AR and inhibitory potencies on noradrenaline-induced contraction or inositol phosphate accumulation in tail artery, confirming that there is a homogeneous functional population of alpha(1A)-AR in this vessel. On the contrary, a poor correlation seems to exist between the affinity of 8-NH (2)-boldine for cloned alpha (1D)-AR and its potency as an inhibitor of noradrenaline-induced contraction or inositol phosphate accumulation in rat aorta, which confirms that a heterogeneous population of alpha (1)-AR mediates the adrenergic response in this vessel.     

Design, synthesis, and structure-activity relationships of phthalimide-phenylpiperazines: a novel series of potent and selective alpha(1)(a)-adrenergic receptor antagonists

Beginning from the screening hit and literature alpha(1)-adrenergic compounds, a hybridized basic skeleton A was proposed as the pharmacophore for potent and selective alpha(1a)-AR antagonists. Introduction of a hydroxy group to increase the flexibility afforded B which served as the screening model and resulted in the identification of the second-generation lead 1. Using the Topliss approach, a number of potent and selective alpha(1a)-AR antagonists were discovered. In all cases, binding affinity and selectivity at the alpha(1a)-AR of S-hydroxy enantiomers were higher than those of the R-hydroxy enantiomers. As compared to the des-hydroxy analogues, the S-hydroxy enantiomers had slightly lower binding affinity at alpha(1a)-AR but gained more than 2-fold selectivity for alpha(1a)-AR over alpha(1b)-AR, and 2- to 6-fold selectivity for alpha(1a)-AR over alpha(1d)-AR. They also had less cross activities against a panel of 25-35 peripheral and CNS receptors. The S-hydroxy enantiomers 23 and 24 (K(i) = 0.29 nM, 0.33 nM; alpha(1b)/alpha(1a) >5690, >6060; alpha(1d)/alpha(1a) = 186, 158, respectively) were slightly less potent but much more selective at alpha(1a)-AR than tamsulosin (K(i) = 0.13 nM, alpha(1b)/alpha(1a) = 14.8, alpha(1d)/alpha(1a) = 1.4). In the functional assay, the S-hydroxy enantiomers 20, 23, and 24 were less potent than tamsulosin in inhibiting contractions of rat prostate tissue but more selective in the inhibition of tissue contractions of rat prostate versus rat aorta. Compound 24 was selected as the development candidate for the treatment of BPH.     

Buspirone analogues. 1. Structure-activity relationships in a series of N-aryl- and heteroarylpiperazine derivatives

A series of analogues of buspirone was synthesized in which modifications were made in the aryl moiety, alkylene chain length, and cyclic imide portion of the molecule. These compounds were tested in vitro for their binding affinities to rat brain membrane sites labeled by either the dopamine antagonist [3H]spiperone or the alpha 1-adrenergic antagonist [3H]WB-4101. Compounds were also tested in vivo for tranquilizing properties and induction of catalepsy. Potency at the [3H]spiperone binding site was affected by alkylene chain length and imide portion composition. Nonortho substituents on the aryl moiety had little effect on [3H]spiperone binding affinity. Structure-activity relationships of ortho substituents demonstrated only modest correlations between the receptor binding data and physical parameters of the substituents. The complex nature of the drug-receptor interactions may be understood in terms of the fit of buspirone to a hypothetical model of the dopamine receptor.     

Effect of the amide fragment on 5-HT1A receptor activity of some analogs of MP 3022

A new set (3-11) of analogs of MP 3022 (1) containing the amide bond inserted into the intermediate chain linking the terminal heteroaromatic and 1-(2-methoxyphenyl)piperazine moieties were prepared and their 5-HT1A and 5-HT2A receptor affinities were determined. Only compounds with trimethylene chain between amide and arylpiperazine fragments (5a, 5b, 7a, 7b and 11) showed satisfactory affinity for 5-HT1A receptor (Ki = 42-87 nM) and high 5-HT2A/5-HT1A selectivity. The new 5-HT1A receptor ligands were investigated in vivo to determine their 5-HT1A agonistic or antagonistic properties. Compounds 7a and 7b with terminal indazole fragment as well as 11 with phenyl substituent behaved like weak 5-HT1A receptor antagonists. The structure-affinity relationship studies in this series of compounds revealed that the amide group along with the terminal aromatic fragments contributed to interaction with 5-HT1A receptor sites, whereas in vivo results indicated that introduction of the amide group into presented arylpiperazine structures was not a profitable modification for their 5-HT1A functional activity.     

Dopamine D1/D5 receptor antagonists with improved pharmacokinetics: design, synthesis, and biological evaluation of phenol bioisosteric analogues of benzazepine D1/D5 antagonists

Benzazepines 1 and 2 (SCH 23390 and SCH 39166, respectively) are two classical benzazepine D1/D5 antagonists, with Ki values 1.4 and 1.2 nM, respectively. Compound 2 has been in human clinical trials for a variety of diseases, including schizophrenia, cocaine addition, and obesity. Both 1 and 2 displayed low plasma levels and poor oral bioavailability, due to rapid first-pass metabolism of the phenol moieties. Several heterocyclic systems containing an N-H hydrogen bond donor were synthesized and evaluated as phenol isosteres. The preference orientation of the hydrogen bond was established by comparison of analogues containing different NH vectors. Replacement of the phenol group of 2 with an indole ring generated the first potent D1/D5 antagonist 11b. Further optimization led to the synthesis of very potent benzimidazolones 19, 20 and benzothiazolone analogues 28, 29. These compounds have excellent selectivity over D2-D4 receptors, alpha2a receptor, and the 5-HT transporter. Compared to 2, these heterocyclic phenol isosteres showed much better pharmacokinetic profiles as demonstrated by rat plasma levels. In sharp contrast, similar phenolic replacements in 1 decreased the binding affinity dramatically, presumably due to a conformational change of the pendant phenyl group. However, one indazole compound 33 was identified as a potent D1/D5 ligand in this series.     

2,4-二甲氧基苯乙胺类α1-肾上腺素受体拮抗剂的合成、生物活性研究

目的设计合成苯乙胺类α1-肾上腺素受体（α1-AR）拮抗剂,并研究它们对大鼠肛尾肌收缩功能的影响。方法以DDPH为先导化合物设计合成了11个新化合物,以2,6-二甲基苯酚为原料经多步反应得中间体卤代苯氧丙酮,再经还原胺化得目标物。运用大鼠肛尾肌收缩功能实验测定目标物的拮抗活性。结果共合成了11个目的物,其结构经IR、HRMS1、H-NMR确证。结论生物活性测试显示大部分目标化合物均具有一定的α1-AR拮抗活性,化合物Ⅲk拮抗作用和DDPH接近。     

一种新的α1A肾上腺素受体选择性拮抗剂—Sertindole

本工作分别在稳定表达α_1A,α_1B和α_1D肾上腺素受体(adrenoceptor,AR)的人胚胎肾脏细胞( human embryonic kidney 293,HEK 293)和大鼠离体血管上,用放射配体结合实验和离体血管收缩功能实验方法以确定sertindole对α₁-AR亚型的选择性拮抗作用。结果显示sertindole与克隆α_1A-AR的亲和性分别是与克隆α_1B-AR和克隆α_1D-AR的69倍和132倍。Sertindole拮抗去甲肾上腺素引起的主动脉和肾动脉收缩反应的pA₂值分别与其对α_1D和α_1A亚型的pKI值相符。分别稳定表达3种亚型受体的HEK293细胞膜标本经与sertindole预温育30min后,受体与¹²⁵IBE2254结合的B_max值显著降低,KD值无显著变化;而在 sertindole 存在条件下,α₁-AR3种亚型与¹²⁵IBE2254 结合的KD值显著增大,但B_max值无显著改变。上述结果表明sertindole为不可逆性竞争性α₁-AR拮抗剂,并有α_1A亚型选择性。     

Synthesis and pharmacological evaluation of new 1-[3-(4-arylpiperazin-1-yl)-2-hydroxypropyl]-pyrrolidin-2-one derivatives with anti-arrhythmic, hypotensive, and alpha-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.     

Binding and functional affinity of sarpogrelate, its metabolite m-1 and ketanserin for human recombinant alpha-1-adrenoceptor subtypes

Serotonin (5-HT(2)) antagonists show high affinity for the alpha(1)-adrenoceptor (alpha(1)-AR) in addition to the 5-HT(2) receptor. In the present study we compared the pharmacological characteristics of a new 5-HT(2) antagonist sarpogrelate and its active metabolite M-1 with those of ketanserin on human recombinant alpha(1)-AR subtypes. In the binding study, sarpogrelate, M-1 and ketanserin produced concentration-dependent inhibition of (3)H-prazosin binding to alpha(1)-ARs. Among the three drugs, ketanserin showed the highest affinity for alpha(1a)-, alpha(1b)- and alpha(1d)-ARs (pKi 8.0, 8.3 and 7.6, respectively). Sarpogrelate had a relatively low affinity for the three subtypes (6.3, 6.4 and 6.3, respectively) and M-1 showed medium affinity (7.1, 7.1 and 6.1, respectively). Chinese hamster ovary (CHO) cells expressing each alpha(1)-AR subtype showed concentration-dependent inositol phosphate (IP) accumulation in response to phenylephrine. The concentration response curves were shifted to the right by three drugs, and the pKb values were close to the pKi values in the binding study. In addition to these effects, sarpogrelate and M-1, but not ketanserin produced an increase in the basal IP level of alpha(1d)-expressed CHO cells, although the increase was less than that of phenylephrine. The present results indicate that sarpogrelate and M-1 have antagonistic activity to the three alpha(1)-AR subtypes, but their affinities are significantly lower than those of ketanserin.