I(2)-imidazoline binding site affinity of a structurally different type of ligands

Ligands with Two Monoanionic N,N-Binding Sites: Synthesis and Coordination Chemistry

Polytopic ligands have become ubiquitous in coordination chemistry because they grant access to a variety of mono- and polynuclear complexes of transition metals as well as rare-earth and main-group elements. Nitrogen-based ditopic ligands, in which two monoanionic N,N-binding sites are framed within one molecule, are of particular importance and are therefore the primary focus of this review. In detail, bis(amidine)s, bis(guanidine)s, bis(β-diimine)s, bis(aminotroponimine)s, bis(pyrrolimine)s, and miscellaneous bis(N,N-chelating) ligands are reviewed. In addition to the general synthetic protocols, the application of these ligands is discussed along with their coordination chemistry, the multifarious binding modes, and the ability of these ligands to bridge two (or more) metal(loids).

Targeting quorum sensing by designing azoline derivatives to inhibit the N-hexanoyl homoserine lactone-receptor CviR: Synthesis as well as biological and theoretical evaluations

To counteract bacterial resistance, we investigated the interruption of quorum sensing mediated by non-classical bioisosteres of the N-hexanoyl homoserine lactone with an azoline core. For this purpose, a set of selected 2-substituted azolines was synthesized, establishing the basis for a new protocol to synthesize 2-amino imidazolines. The synthesized compounds were evaluated as inhibitors of violacein production in Chromobacterium violaceum. Theoretical studies on bioisostere-protein interactions were performed using CviR. The results show that some azolines decreased violacein production, suggesting an antiquorum sensing profile against Gram-negative bacteria. Docking and molecular dynamic simulations together with binding free energy calculations revealed the exact binding and inhibitory profiles. These theoretical results show relationship with the in vitro activity of the azoline series.

The imidazoline receptors and ligands in pain modulation

Pain is an unpleasant experience and effects daily routine negatively. Although there are various drugs, many of them are not entirely successful in relieving pain, since pain modulation is a complex process involving numerous mediators and receptors. Therefore, it is a rational approach to identify the factors involved in the complex process and develop new agents that act on these pain producing mechanisms. In this respect, the involvement of the imidazoline receptors in pain modulation has drawn attention in recent years. In this review, it is aimed to focus on the imidazoline receptors and their ligands which contribute to the pain modulation. It is demonstrated that imidazoline-2 (I2) receptors are steady new drug targets for analgesics. Even if the mechanism of I2 receptor is not well known in the modulation of pain, it is known that it plays a role in tonic and chronic pain but not in acute phasic pain. Moreover, the I2 receptor ligands increase the analgesic effects of opioids in both acute and chronic pain and prevent the development of opioid tolerance. So, they are valuable for the chronic pain treatment and also therapeutic coadjuvants in the management of chronic pain with opiate drugs due to the attenuation of opioid tolerance and addiction. Thus, the use of the ligands which bind to the imidazoline receptors is an effective strategy for relieving pain. This educational forum exhibits the role of imidazoline receptors and ligands in pain process by utilizing experimental studies.

Influence of ornithine decarboxylase antizymes and antizyme inhibitors on agmatine uptake by mammalian cells

Agmatine (4-aminobutylguanidine), a dicationic molecule at physiological pH, exerts relevant modulatory actions at many different molecular target sites in mammalian cells, having been suggested that the administration of this compound may have therapeutic interest. Several plasma membrane transporters have been implicated in agmatine uptake by mammalian cells. Here we report that in kidney-derived COS-7 cell line, at physiological agmatine levels, the general polyamine transporter participates in the plasma membrane translocation of agmatine, with an apparent Km of 44 ± 7 µM and Vmax of 17.3 ± 3.3 nmol h(-1) mg(-1) protein, but that at elevated concentrations, agmatine can be also taken up by other transport systems. In the first case, the physiological polyamines (putrescine, spermidine and spermine), several diguanidines and bis(2-aminoimidazolines) and the polyamine transport inhibitor AMXT-1501 markedly decreased agmatine uptake. In cells transfected with any of the three ornithine decarboxylase antizymes (AZ1, AZ2 and AZ3), agmatine uptake was dramatically reduced. On the contrary, transfection with antizyme inhibitors (AZIN1 and AZIN2) markedly increased the transport of agmatine. Furthermore, whereas putrescine uptake was significantly decreased in cells transfected with ornithine decarboxylase (ODC), the accumulation of agmatine was stimulated, suggesting a trans-activating effect of intracellular putrescine on agmatine uptake. All these results indicate that ODC and its regulatory proteins (antizymes and antizyme inhibitors) may influence agmatine homeostasis in mammalian tissues.

Antiprotozoal activity of 1-phenethyl-4-aminopiperidine derivatives

A series of 44 4-aminopiperidine derivatives was screened in vitro against four protozoan parasites (Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani, and Plasmodium falciparum). This screening identified 29 molecules selectively active against bloodstream-form T. b. rhodesiense trypomastigotes, with 50% inhibitory concentrations (IC50) ranging from 0.12 to 10 microM, and 33 compounds active against the chloroquine- and pyrimethamine-resistant K1 strain of P. falciparum (IC50 range, 0.17 to 5 microM). In addition, seven compounds displayed activity against intracellular T. cruzi amastigotes in the same range as the reference drug benznidazole (IC50, 1.97 microM) but were also cytotoxic to L-6 cells, showing little selectivity for T. cruzi. None of the molecules tested showed interesting antileishmanial activity against axenic amastigotes of L. donovani. To our knowledge, this is the first report of the antitrypanosomal activity of molecules bearing the 4-aminopiperidine skeleton.

On the search of new I2-IBS aliphatic ligands: Bis-guanidino carbonyl derivatives

Continuing with our search of aliphatic dicationic derivatives as I2-IBS ligands and looking at Amiloride, a known ligand of I2-IBS, we have incorporated the guanidinocarbonyl moiety into our aliphatic compounds with the intention of improving the binding to I2-IBS. Thus, we present the different approaches to the preparation and pharmacological evaluation (in human brain tissue) as I2-IBS ligands of a new series of aliphatic derivatives incorporating the guanidinocarbonyl group and with different chain length (n= 8-12, and 14 methylene groups).

Guanidine and 2-Aminoimidazoline Aromatic Derivatives as α2-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.

N, N' (4,5-dihydro-1h-imidazol-2-yl)3-aza-1,10-decane-diamine and N, N'(4,5-dihydro-1H-imidazol-2-yl)3-aza-1, 10-dodecane-diamine antagonize cell proliferation as selective ligands towards topoisomerase II

New alkyl imidazoline derivatives have been synthesized as potential anti-cancer agents. The anti-proliferative activity of these compounds, evaluated against representative human haematological and solid neoplastic cell lines, showed that N, N'-di (4,5-dihydro-1H-imidazol-2-yl)3-aza-1,10-decane-diamine (8) and N, N'-di (4,5-dihydro-1H-imidazol-2-yl)3-aza-1,10-dodecane-diamine (9) were the most active compounds; in fact, they inhibited the cell proliferation at submicromolar concentrations. In enzyme assays, compound 9 turned out to be an inhibitor of topoisomerase II at concentrations comparable with those of the reference topoisomerase II inhibitor, etoposide.

Synthesis and pharmacological studies of new hybrid derivatives of fentanyl active at the mu-opioid receptor and I2-imidazoline binding sites

Two series of fentanyl-derived hybrid molecules bearing potent I2-imidazoline binding site (IBS) ligands (i.e., guanidine and BU224 moieties) linked with an aliphatic (m=2, 3, 4, 6, 7, 8, 9 and 12 methylene units) or aromatic spacer were prepared. Their affinities for the mu-opioid receptors and for the I2-IBS were determined through competition binding studies on human postmortem brain membranes. Whereas the BU224 hybrid molecules bound to the mu-opioid receptor and the I2-IBS in the micromolar to low micromolar range, the alkaneguanidine series exhibited remarkable affinities in the nanomolar range for both receptors. [35S]GTPgammaS functional assays were performed on human postmortem brain membranes with selected ligands from each series (4f and 8g) showing the highest dual affinity for the mu-opioid receptor and I2-IBS affinities. Both compounds displayed agonist properties: at the mu-opioid receptor for the alkaneguanidine derivative 4f (spacer: six methylene units) and at a G-protein coupled receptor (GPCR) which remains to be determined for 8g. The lack of analgesic properties of 4f in vivo (i.e., hot plate and writhing tests in mice), discordant with the good in vitro binding data (Ki mu=1.04+/-0.28 nM, Ki I2=409+/-238 nM), may possibly be due to the low intrinsic efficacy of the compound. Alternatively, a low access to the central nervous system for this kind of hybrid molecules cannot be ruled out. Two new compounds reported here (9f and 13), which were not dual acting, are worth mentioning for their outstanding binding affinities; 9f bound to the mu-opioid receptor with a picomolar affinity (Ki=0.0098+/-0.0033 nM), whereas 13 presented an I2-IBS affinity (Ki=18+/-11 nM) similar to the reference compound BU224.

Imidazoline binding sites and their ligands: an overview of the different chemical structures

Since Bousquet et al. discovered the imidazoline binding sites (IBS) two decades ago, when they realized that the antihypertensive drug clonidine interacts not only with the alpha2-adrenenoceptors (alpha2-AR) but also with a distinct imidazoline preferring binding site, these receptors have been paid a great deal of attention. At least two subtypes, I1 and I2, have been characterised based on their binding affinity for different radioligands, but their structures still remain unknown. The pharmacological profile of these IBSs has been the objective of several and very thorough reviews. However, a medicinal chemistry overview of the different IBS ligands prepared to date has never been attempted. In this study, we attempt to compile all the different chemical structures reported to date as IBS ligands and classify them in function of their chemical structure and binding affinity for the different IBS subtypes. Thus, we comment on the different endogenous IBS ligands known as well as the drugs described to interact with the I1-IBS which have found application as antihypertensive drugs. Then, we review those compounds described in the literature to interact with the I2-IBS, classifying them by their chemical families (imidazolines, guanidines, 2-aminoimidazolines, beta-carbolines). Finally, some conclusions are drawn.

Fentanyl derivatives bearing aliphatic alkaneguanidinium moieties: a new series of hybrid molecules with significant binding affinity for mu-opioid receptors and I2-imidazoline binding sites

A new series of fentanyl derivatives [i.e., N-[1-(2-phenethyl)-4-piperidyl]-N-(guanidinoalkyl)propanamide] bearing aliphatic alkaneguanidinium moieties were prepared. Their affinities for the micro opioid receptors and for the I(2)-imidazoline binding sites (I(2)-IBS) were determined on human post-mortem prefrontal cortex membranes. All of these hybrid compounds had significant and/or very high affinity for both receptors in the nanomolar range, meaning an improvement compared to the prototype N-[1-(2-phenethyl)-4-piperidyl]-N-(guanidinopropyl)propanamide previously reported.

Bisguanidine, Bis(2-aminoimidazoline), and Polyamine Derivatives as Potent and Selective Chemotherapeutic Agents against Trypanosoma brucei rhodesiense. Synthesis and in Vitro Evaluation

The in vitro screening for trypanocidal activity against Trypanosoma brucei rhodesiense of an in-house library of 62 compounds [i.e. alkane, diphenyl, and azaalkane bisguanidines and bis(2-aminoimidazolines)], which were chosen for their structural similarity to the trypanocidal agents synthalin (1,10-decanediguanidine) and 4,4'-diguanidinodiphenylmethane and the polyamine N(1)-(3-amino-propyl)propane-1,3-diamine, respectively, is reported. The original synthetic procedure for the preparation of 21 of these compounds is also reported. Most compounds displayed low micromolar antitrypanosomal activity, with five of them presenting a nanomolar inhibitory action on the parasite: 1,9-nonanediguanidine (1c), 1,12-dodecanediguanidine (1d), 4,4'-bis[1,3-bis(tert-butoxycarbonyl)-2-imidazolidinylimino]diphenylamine (28a), 4,4'-bis(4,5-dihydro-1H-2-imidazolylamino)diphenylamine (28b), and 4,4'-diguanidinodiphenylamine (32b). Those molecules that showed an excellent in vitro activity as well as high selectivity for the parasite [e.g. 1c (IC(50) = 49 nM; SI > 5294), 28b (IC(50) = 69 nM; SI = 3072), 32b (IC(50) = 22 nM; SI = 29.5), 41b (IC(50) = 118 nM; SI = 881)] represent new antitrypanosomal lead compounds.

Synthesis and biological evaluation of new 2-(4,5-dihydro-1H-imidazol-2-yl)-3,4-dihydro-2H-1,4-benzoxazine derivatives

2-(4,5-Dihydro-1H-imidazol-2-yl)-3,4-dihydro-2H-1,4-benzoxazine derivatives and tricyclic analogues with a fused additional ring on the nitrogen atom of the benzoxazine moiety have been prepared and evaluated for their cardiovascular effects as potential antihypertensive agents. The imidazoline ring was generated by reaction of the corresponding ethyl ester with ethylenediamine. Affinities for imidazoline binding sites (IBS) I(1) and I(2) and alpha(1) and alpha(2) adrenergic receptors were evaluated as well as the effects on mean arterial blood pressure (MAP) and heart rate (HR) of spontaneously hypertensive rats. With few exceptions the most active compounds on MAP were those with high affinities for IBS and alpha(2) receptor. Among these, compound 4h was the most interesting and is now, together with its enantiomers, under complementary pharmacological evaluation.

Synthesis and analgesic activity of a series of new azaalkane bis-guanidinium and bis(2-aminoimidazolinium) compounds

In the present paper, we wish to report the synthesis and antinociceptive activity of a series of new azaalkane bis(2-aminoimidazolinium) compounds from which, N,N'-di(4,5-dihydro-1H-imidazol-2-yl)-3-aza-1,6-hexanediamine 2a has shown the best analgesic properties in vivo in two different assays (i.e., acetic acid-induced writhing test and hot-plate test in mice), as well as oral bioavailability.