Deconstruction - Reconstruction: Analysis of the Crucial Structural Elements of GluN2B-Selective, Negative Allosteric NMDA Receptor Modulators with 3-Benzazepine Scaffold.

BACKGROUND/AIMS: The NMDA receptor plays a key role in the pathogenesis of neurodegenerative disorders including Alzheimer's and Huntington's disease, as well as depression and drug or alcohol dependence. Due to its participation in these pathologies, the development of selective modulators for this ion channel is a promising strategy for rational drug therapy. The prototypical negative allosteric modulator ifenprodil inhibits selectively GluN2B subunit containing NMDA receptors. It was conformationally restricted as 2-methyl-3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine-1,7-diol, which showed high GluN2B affinity and inhibitory activity. For a better understanding of the relevance of the functional groups and structural elements, the substituents of this 3-benzazepine were removed successively (deconstruction). Then, additional structural elements were introduced (reconstruction) with the aim to analyze, which additional modifications were tolerated by the GluN2B receptor. METHODS: The GluN2B affinity was recorded in radioligand receptor binding studies with the radioligand [3H]ifenprodil. The activity of the ligands was determined in two-electrode voltage clamp experiments using Xenopus laevis oocytes transfected with cRNA encoding the GluN1-1a and GluN2B subunits of the NMDA receptor. Docking studies showed the crucial interactions with the NMDA receptor protein. RESULTS: The deconstruction approach showed that removal of the methyl moiety and the phenolic OH moiety in 7-positon resulted in almost the same GluN2B affinity as the parent 3-benzazepine. A considerably reduced GluN2B affinity was found for the 3-benzazepine without further substituents. However, removal of one or both OH moieties led to considerably reduced NMDA receptor inhibition. Introduction of a NO2 moiety or bioisosteric replacement of the phenol by a benzoxazolone resulted in comparable GluN2B affinity, but almost complete loss of inhibitory activity. An O-atom, a carbonyl moiety or a F-atom in the tetramethylene spacer led to 6-7-fold reduced ion channel inhibition. CONCLUSION: The results reveal an uncoupling of affinity and activity for the tested 3-benzazepines. Strong inhibition of [3H]ifenprodil binding by a test compound does not necessarily translate into strong inhibition of the ion flux through the NMDA receptor associated ion channel. 3-(4-Phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine- 1,7-diol (WMS-1410) shows high GluN2B affinity and strong inhibition of the ion channel. Deconstruction by removal of one or both OH moieties reduced the inhibitory activity proving the importance of the OH groups for ion channel blockade. Reconstruction by introduction of various structural elements into the left benzene ring or into the tetramethylene spacer reduced the NMDA receptor inhibition. It can be concluded that these modifications are not able to translate binding into inhibition.

Synthesis and biological activities of 2-[(heteroaryl)methyl]imidazolines.

A series of 2-[(heteroaryl)methyl]imidazolines was synthesized and tested for their activities at α(1)- and α(2)-adrenoceptors and imidazoline I(1) and I(2) receptors. The most active 2-[(indazol-1-yl)methyl]imidazolines showed high or moderate affinities for α(1)- and α(2)-adrenoceptors. However, their intrinsic activities at α(2A)-adrenoceptors proved to be negligible. A selected 7-chloro derivative behaved as a potent α(1)-adrenoceptor antagonist and exhibited peripherally mediated hypotensive effects in rats.

Synthesis and biological activity of 5-styryl and 5-phenethyl-substituted 2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indoles.

Syntheses, biological evaluation, and structure-activity relationships for a series of novel 5-styryl and 5-phenethyl analogs of dimebolin are disclosed. The novel derivatives and dimebolin share a broad spectrum of activities against therapeutically relevant targets. Among all synthesized derivatives, 2,8-dimethyl-5-[(Z)-2-phenylvinyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole and its 5-phenethyl analog are the most potent blockers of 5-HT(7), 5-HT(6), 5-HT(2C), Adrenergic alpha(2) and H(1) receptors. The general affinity rank order towards the studied receptors was Z-3(2)>4(2)4(3)>>dimebolin, all of them having highest affinities to 5-HT(7) receptors.

Reactive derivatives for affinity labeling in the ifenprodil site of NMDA receptors.

To prepare thiol-reactive ifenprodil derivatives designed as potential probes for cysteine-substituted NR2B containing NMDA receptors, electrophilic centers were introduced in different areas of the ifenprodil structure. Intermediates and final compounds were evaluated by binding studies and by electrophysiology to determine the structural requirements for their selectivity. The reactive compounds were further tested for their stability and for their reactivity in model reactions; some were found suitable as structural probes to investigate the binding site and the docking mode of ifenprodil in the NR2B subunit.

New practical synthesis of Tamsulosin.

The medicine called Tamsulosin was produced 25 years ago and since then almost 10 new synthesis route has been known. Each process shows the researchers' workstyle, every year, which mainly differs in the way of separating the enantiomers. The applied reaction steps also reflect the development over the past 25 years and the new synthesis is influenced by the antecedents. The key-intermediate used in our new method is a racemic secondary amine derivative, which is unknown in the literature before and for resolving it, we worked out a quite advantegeous process. By using an optically active secondary amine, side reactions can be avoided.

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.

Structure-activity relationship of quinoline derivatives as potent and selective alpha(2C)-adrenoceptor antagonists.

Starting from two acridine compounds identified in a high-throughput screening campaign (1 and 2, Table 1), a series of 4-aminoquinolines was synthesized and tested for their properties on the human alpha(2)-adrenoceptor subtypes (alpha(2A), alpha(2B), and alpha(2C)). A number of compounds with good antagonist potencies against the alpha(2C)-adrenoceptor and excellent subtype selectivities over the other two subtypes were discovered. For example, (R)-{4-[4-(3,4-dimethylpiperazin-1-yl)phenylamino]quinolin-3-yl}methanol 6j had an antagonist potency of 8.5 nM against, and a subtype selectivity of more than 200-fold for, the alpha(2C)-adrenoceptor. Investigation of the structure-activity relationship identified a number of structural features, the most critical of which was an absolute need for a substituent in the 3-position of the quinoline ring. The 3-position on the piperazine ring was also found to play an appreciable role, as substitutions in that position exerted a significant and stereospecific beneficial effect on the alpha(2C)-adrenoceptor affinity and potency. Replacing the piperazine ring proved difficult, with 1,4-diazepanes representing the only viable alternative.

Structure-activity relationships in 1,4-benzodioxan-related compounds. 8.(1) {2-[2-(4-chlorobenzyloxy)phenoxy]ethyl}-[2-(2,6-dimethoxyphenoxy)ethyl]amine (clopenphendioxan) as a tool to highlight the involvement of alpha1D- and alpha1B-adrenoreceptor subtypes in the regulation of human PC-3 prostate cancer cell apoptosis and proliferation.

A series of new alpha1-adrenoreceptor antagonists (5-18) was prepared by introducing various substituents (Topliss approach) into the ortho, meta, and para positions of the benzyloxy function of the phendioxan open analogue 4 ("openphendioxan"). All the compounds synthesized were potent antagonists and generally displayed, similarly to 4, the highest affinity values at alpha1D- with respect to alpha1A- and alpha1B-AR subtypes and 5-HT1A subtype. By sulforhodamine B (SRB) assay on human PC-3 prostate cancer cells, the new compounds showed antitumor activity (estimated on the basis of three parameters GI50, TGI, LC50), at low micromolar concentration, with 7 ("clopenphendioxan") exhibiting the highest efficacy. Moreover, this study highlighted for the first time alpha1D- and alpha1B-AR expression in PC3 cells and also demonstrated the involvement of these subtypes in the modulation of apoptosis and cell proliferation. A significant reduction of alpha1D- and alpha1B-AR expression in PC3 cells was associated with the apoptosis induced by 7. This depletion was completely reversed by norepinephrine.

Design, synthesis, and biological evaluation of prazosin-related derivatives as multipotent compounds.

To combine in the same molecule alpha(1)-adrenoreceptor blocking and antioxidant properties, compounds 2-5 were designed and synthesized. All compounds were effective alpha(1)-adrenoreceptor antagonists and were tested in both functional and binding assays. In addition, compounds 2 and 5 also displayed significant capacity to inhibit intracellular oxidative stress, whereas 3-5 exerted potent antiproliferative activity in lymph node carcinoma of prostate cells.

Synthesis and in vitro pharmacological activity of oxypropanol analogs of labetalol.

New oxypropanol alpha- and beta-adrenoceptor blocking agents, analogs of labetalol, were synthesised and studied in vitro in left atria and aorta for alpha and beta activity.

Arylpiperazines with affinity toward alpha(1)-adrenergic receptors.

In the last years, alpha(1) adrenoceptors (alpha(1)-AR) have been the subject of intense research, in part because receptor-binding studies and molecular biology have opened up new aspects of understanding but also because of the potential to find new drugs possibly acting toward pathophysiological processes where alpha(1)-AR are involved, such as benign prostatic hyperplasia (BPH) or hypertension. At present, arylpiperazines represent one of the most studied classes of molecules with affinity at alpha(1)-AR. In fact, a large amount of work has been done and reported, describing synthetic procedures, biological evaluation at both alpha(1)-AR and the corresponding subtypes, and structure-activity relationships (SARs). In this paper, a review based on a literature survey aimed at focusing on the structural properties that a compound should possess to show affinity toward alpha(1)-AR is presented. Moreover, the identification and optimization of the structural features of a hit compound derived from a pharmacophore-based database search, leading to a new class of arylpiperazinylalkyl pyridazinone derivatives with alpha(1)-AR affinity is reported.

Synthesis and alpha 2-adrenoceptor antagonist activity of some disulfonamidobenzoquinolizines.

A series of disulfonamidobenzo[a]quinolizines were synthesized and evaluated for their alpha 2- and alpha 1-adrenoceptor antagonist activity on the rat vas deferens and anococcygeus muscle, respectively. N-((2 beta,11b alpha)-1,3,4,6,7,11b-Hexahydro-2H-benzo[a]quinolizin-2-yl)-N- [2-[(methylsulfonyl)amino]ethyl]methanesulfonamide (4) and its N-[2-[(methylsulfonyl)amino]ethyl]ethanesulfonamide (22), N-[2-[(ethylsulfonyl)amino]ethyl]ethanesulfonamide (27), and N-[2-[(methylsulfonyl)amino]ethyl]-4-methylbenzenesulfonamide (30) analogues showed 400-fold or greater selectivity in favor of alpha 2- over alpha 1-adrenoceptor blockade.

1,3-Diamino-6,7-dimethoxyisoquinoline derivatives as potential alpha 1-adrenoceptor antagonists.

Treatment of 2-methyl-4,5-dimethoxybenzonitrile (3) with LDA followed by reaction with an N,N-disubstituted cyanamide provided a series of 1,3-diamino-6,7-dimethoxyisoquinolines (2), which were evaluated for alpha-adrenoceptor binding affinity and antihypertensive activity. 1-Amino-3-(dimethylamino)-6,7-dimethoxyisoquinoline (4) showed no significant affinity (Ki much greater than 10(-6) M) for alpha 1-adrenoceptors, while the corresponding 3-(2-furoylpiperazin-1-yl) analogue (8; Ki = 1.6 X 10(-7) M) was some 1000-fold less potent than prazosin. pKa data showed that N-2 protonation (34%) of 4 (pKa = 7.1) would occur at physiological pH, in agreement with X-ray crystallographic analysis of 8.HCl. Comparison of positive charge distribution following protonation of 4 with the corresponding quinoline and quinazoline cations confirmed N-1 protonation is required for these heterocyclic nuclei to bind efficiently to the alpha 1-adrenoceptor. Computer-assisted comparison of the X-ray structures of 8 and prazosin suggested that the 4.0 kcal/mol difference in alpha 1-adrenoceptor binding energies was largely due to salt-bridge formation (ca. 3.0 kcal/mol) between the protonated quinazoline and the receptor protein. None of the isoquinolines (2) proved to be effective antihypertensive agents in rats even when administered at relatively high doses (10 mg/kg). These results support the hypothesis that the antihypertensive activity of prazosin, doxazosin, and related derivatives derives solely from alpha 1-adrenoceptor blockade.

Studies on quinazolines. 5. 2,3-dihydroimidazo[1,2-c]quinazoline derivatives: a novel class of potent and selective alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 2-[(substituted phenylpiperazin-1-yl)methyl]- and 2-[(substituted phenylpiperidin-1-yl)methyl]-2,3-dihydroimidazo[1,2- c]quinazolin-5(6H)-ones or -5(6H)-thiones, and 3-[(substituted phenylpiperazin-1-yl)methyl]-2,3-dihydroimidazo[1,2-c]quinaz oline derivatives were synthesized, as conformationally restricted analogues of SGB-1534 and ketanserin, for evaluation as alpha-antagonists and antihypertensive agents. Most compounds containing a (substituted phenylipiperazinyl)methyl side chain displayed high binding affinity for alpha 1-adrenoceptor with no significant activity at alpha 2-sites. Compounds having a (substituted phenylpiperazinyl)methyl at the 3-position of 2,3-dihydroimidazo[1,2-c]quinazolin-5(6H)-one ring system had a better activity than those with the same substituent at the 2-position. Structure-activity relationships for alpha 1-adrenoceptor affinity are presented and indicate that compounds with substitution at the ortho position on the benzene ring of the phenylpiperazine side chain moiety are more potent than those without substitution and/or substitutions at the 3- and 4-positions. Computer-assisted superimposition of SGB-1534 and 20b showed little structural correspondence between the quinazolinone and 2,3-dihydroimidazo[1,2-c]quinazoline nucleus, and specific interactions of these molecular fragments with the receptor protein appear unlikely. Antihypertensive activity was evaluated via intravenous administration of each compound to spontaneously hypertensive rats, and compounds (16a, 16b, 20b, and 28b) illustrated similar efficacy to SGB-1534 when assessed after 6 h. The pA2 value for 16a against phenylephedrine in rat aorta was much higher than that of prazosin. On the basis of alpha 1-adrenoceptor affinity/selectivity in vitro and duration of antihypertensive action in vivo, compounds 20b and 28b warrant further evaluation.

2,4-Diamino-6,7-dimethoxyquinoline derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 2,4-diamino-6,7-dimethoxyquinoline derivatives (2), prepared by LDA- or ZnCl2-mediated intramolecular cyclization of an N-[1-(dialkylamino)ethylidene]-2-cyano-4,5-dimethoxyaniline (3), was evaluated for alpha-adrenoceptor affinity and antihypertensive activity. Most compounds displayed high in vitro binding affinities (Ki's, 10(-10) M) for alpha 1-adrenoceptors with alpha 1-/alpha 2-selectivity ratios of at least 10,000. 4-Amino-2-[4-(2-furoyl)piperazin-1-yl]-6,7-dimethoxyquinoline++ + (14) proved to be the most potent member (Ki = 1.4 X 10(-10) M) of series 2, and displayed no activity at alpha 2-adrenoceptor binding sites at concentrations up to 10(-6) M. In the rabbit pulmonary artery, 14 was a highly potent (pA2 = 9.76 +/- 0.26) competitive antagonist of the alpha 1-mediated vasoconstrictor action of noradrenaline and was some 20 times more active than prazosin. pKa measurements confirmed that, at physiological pH, N-1 protonation of series 2 would efficiently provide 1b, a key pharmacophore for alpha 1-adrenoceptor recognition. Antihypertensive activity for series 2 was evaluated after oral administration (3 mg/kg) to spontaneously hypertensive rats (SHR) and falls in blood pressure were determined at 1 and 4.5 h. Various quinoline derivatives (2) proved to be effective antihypertensive agents in SHR, with both efficacy and duration of action at least equivalent to prazosin, and 14 displayed the most favorable overall profile. These observations are consistent with the high affinity and selectivity displayed by series 2 for postjunctional alpha 1-adrenoceptors.

Indoline analogues of idazoxan: potent alpha 2-antagonists and alpha 1-agonists.

The synthesis and alpha-adrenergic activity of a series of substituted 2-imidazolinylindolines are described. Substitution in the indoline ring generated compounds with a spectrum of adrenoceptor antagonist/agonist profiles that proved sensitive to both the nature and position of the substituent. Many of the derivatives possess greater presynaptic antagonist potency than the corresponding benzodioxan 1, dihydrobenzofuran 2, and indan 3 analogues; however, this alpha 2-antagonism is often accompanied by alpha 1-agonist activity. It was not possible to separate alpha 2-antagonist from alpha 1-agonist properties in this series. Compounds of most interest proved to be the N-ethyl 6, 5-chloro-N-methyl 18, and 5-chloro-N-ethyl 23 derivatives, all being potent alpha 2-antagonists and alpha 1-agonists. Substitution at the 4- and 7-position of the indoline ring generally gave compounds with nonselective agonist properties.

2,4-Diamino-6,7-dimethoxyquinazolines. 3. 2-(4-Heterocyclylpiperazin-1-yl) derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 4-amino-6,7-dimethoxy-2(4-heterocyclylpiperazin-1-yl)quinazolines (3) was prepared and screened for alpha-adrenoceptor affinity and antihypertensive activity. These quinazoline derivatives showed high binding affinity (ca. 10(-10) M) and selectivity (greater than 10,000) for alpha 1-adrenoceptors in vitro, with no relevant activity at alpha 2 sites. Several compounds displayed similar activity to prazosin (Ki = 1.9 X 10(-10) M) while the dimethoxytriazine derivative 30 (Ki = 8 X 10(-11) M) was more potent. Like prazosin (pA2 = 8.37 +/- 0.24), 30 proved to be a potent (pA2 = 8.63 +/- 0.15), competitive antagonist of the alpha 1-mediated vasoconstrictor action of norepinephrine. The high binding affinity of series 3 is most likely due to formation, at physiological pH, of the protonated, alpha 1-adrenoceptor pharmacophore 33, coupled with efficient hydrophobic interactions of the quinazoline 2-substituents. Computer-assisted super-imposition of prazosin and 30 showed little structural correspondence between the furoyl and dimethoxytriazine moieties, and specific interactions of these molecular fragments with the receptor protein appear unlikely. Series 3 was evaluated for antihypertensive activity after oral administration (5 mg/kg) to spontaneously hypertensive rats, and blood pressure was recorded after 1 and 6 h. In vivo performance was markedly dependent on the nature of the distal heterocyclic system and various derivatives demonstrated superior or equivalent profiles to prazosin, with respect to both antihypertensive efficacy and duration of action.

2,4-Diamino-6,7-dimethoxyquinazolines. 2. 2-(4-Carbamoylpiperidino) derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 4-amino-2-(4-carbamoylpiperidino)-6,7-dimethoxyquinazolines (2) were synthesized and evaluated for alpha-adrenoceptor affinity and antihypertensive activity. These compounds displayed high binding affinity (Ki, 10(-9)-10(-10) M) and selectivity for alpha 1-adrenoceptors in vitro, and 12, 14, 21-26, and 29 showed similar potency to prazosin. Compounds 26 and 28 were also shown to be competitive antagonists of the postjunctional, vasoconstrictor action of norepinephrine with no significant activity at prejunctional alpha 2-sites. The high binding affinity for series 2 is rationalized in terms of enhanced basicity of the quinazoline nucleus (pKa's: 12, 7.38; 26, 7.53; prazosin, 6.8) and hydrophobic interactions of the carbamoyl substituents. Molecular mechanics calculations and computer-assisted superimposition suggest that the quinazoline 2-substituents in prazosin and 2 occupy the alpha 1-adrenoceptor site in different manners. Antihypertensive activity was evaluated after oral administration (5 mg/kg) to spontaneously hypertensive rats, and 11, 15, 21, 22, and 26 displayed sustained prazosin-like efficacy at the 6-h time point. The high alpha 1-adrenoceptor affinity demonstrated by series 2 in vitro suggests that these marked, and prolonged, falls in blood pressure result from selective blockade of the alpha 1-mediated vasoconstrictor effects of norepinephrine.

2,4-Diamino-6,7-dimethoxyquinazolines. 4. 2-[4-(substituted oxyethoxy) piperidino] derivatives as alpha 1-adrenoceptor antagonists and antihypertensive agents.

A series of 4-amino-6,7-dimethoxy-2-[4-(substituted oxyethoxy)piperidino] quinazoline derivatives (2) was synthesized and evaluated for alpha-adrenoceptor affinity and antihypertensive activity. Most compounds showed binding affinities within the nanomolar range for alpha 1-receptors, although 25 and 26 showed enhanced potency (Ki, ca. 1.5 X 10(-10) M), equivalent to that of prazosin. Series 2 also displaced [3H]clonidine from alpha 2-adrenoceptors, but at relatively high doses of 10(-6) M, and selectivity for alpha 1 sites still predominated. In a rabbit pulmonary artery preparation, 12, 16, and 25 were potent antagonists of the alpha 1-mediated, postjunctional vasoconstrictor activity of norepinephrine with no effect at the prejunctional alpha 2 sites which modulate transmitter release. Physicochemical measurements gave a pKa of 7.63 +/- 0.10 for 12, and N-1 protonation will be favored (60%) at physiological pH to provide the alpha 1-adrenoceptor pharmacophore, 28. Antihypertensive activity of series 2 was evaluated following oral administration to spontaneously hypertensive rats, and blood pressure was measured after 1 and 6 h. Compounds 12, 13, 16, 23, and 37 displayed moderate efficacy and duration of action in lowering blood pressure, but the plasma half-life (ca. 2 h) of 16 in dogs was not compatible with potential once-daily administration in humans.

Structure-activity relationships for prazosin and WB 4101 analogues as alpha 1-adrenoreceptor antagonists.

Several alpha-adrenoreceptor antagonists were prepared by coupling one of the two moieties of WB 4101 (1) with one of the two moieties of prazosin (2). Their blocking activity and relative selectivity on alpha 1- and alpha 2-adrenoreceptors were evaluated in the isolated rat vas deferens. Although retaining a significant selectivity toward alpha 1-adrenoreceptors, all the drugs were weaker antagonists than the parent compounds 1 and 2. Opening the piperazine ring of 2 gave 3, which displayed a very high activity and selectivity toward alpha 1-adrenoreceptors (alpha 1/alpha 2 = 3890). This may have relevance in understanding the mode of action of prazosin. In addition, 3 may represent a valuable tool in the characterization of alpha-adrenoreceptor subtypes.