Drugs acting on imidazoline receptors: a review of their pharmacology, their use in blood pressure control and their potential interest in cardioprotection

Efficacious One-pot Synthesis of 2-thiazolines and 2-oxazolines Under Solvent and Metal-Free Conditions

Background:

2-oxazolines and 2-thiazolines are important heterocycles due to their extensive applications in chemistry, biochemistry, and pharmacology. Most of the precedent methods for preparing these heterocycles involve one or more drawbacks, including harsh reaction conditions, long reaction times, low yields of products, high temperature, and toxic solvents.

Objective:

The aim of this study was to develop a new and eco-efficient method for the preparation of 2-oxazolines and 2-thiazolines.

Methods:

Amino alcohols were condensed with nitriles in a sealed tube under solvent-free and metal- free conditions.

Results:

Our procedure appears to be highly eco-efficient and promotes quantitative access to 2-oxazolines and 2-thiazolines using simple and minimum manipulation.

Conclusion:

This simple approach allows high conversion for different nitriles yielded from 78 to 99% and easy isolation of the targeted products without further purification. To the best of our knowledge, our procedure is the most efficient and fast method reported to date in terms of chemical yields, number of steps, and atom economy.

Studies of binding by 2-imidazolines to human serum albumin and alpha1-acid glycoprotein by high-performance affinity chromatography

2-Imidazoline drugs are used in a variety of applications, such as the treatment of hypertension and opioid withdrawal. It is known these drugs bind to serum proteins and have significant variations within this class of compounds in the overall level of this binding. However, little specific information is available on the interactions of these compounds with the two major transport proteins for many drugs, human serum albumin (HSA) and alpha₁-acid glycoprotein (AGP). This study examined binding by 2-imidazolines to these proteins by using 25 mm × 2.1 mm i.d. high-performance affinity microcolumns that contained HSA or AGP. The drugs that were examined were antazoline, clonidine, dexmedetomidine, lofexidine, moxonidine, phentolamine, and tizanidine, which represented a wide range of structures and pharmaceutical applications. The major metabolite of lofexidine, N-(2-aminoethyl)-2-(2,6-dichlorophenoxy) propenamide (LADP), was also examined. All these 2-imidazolines were found to have weak-to-moderate binding to HSA, with global affinities that ranged from 1.62 × 10² to 1.07 × 10⁴ M^-1 at pH 7.4 and 37 °C. These compounds had stronger binding with AGP, with global affinities constants ranging from 3.80 × 10² to 1.85 × 10⁴ M^-1. No stereoselectivity was observed by HSA for the enantiomers of dexmedetomidine, lofexidine, or LADP. However, AGP did show some stereoselectivity for lofexidine and LADP but not for dexmedetomidine. These results provide a better understanding of interactions of 2-imidazoline with HSA vs AGP in the circulation and of how this binding can change between drugs within this class of compounds.

Cardioprotective Effect of Anesthetics: Translating Science to Practice

Cardiovascular diseases are the number one cause of mortality in the world, particularly among the aging population. Major adverse cardiac events are also a major contributor to perioperative complications, affecting 2.6% of noncardiac surgeries and up to 18% of cardiac surgeries. Cardioprotective effects of volatile anesthetics and certain intravenous anesthetics have been well-documented in preclinical studies; however, their clinical application has yielded conflicting results in terms of their efficacy. Therefore, better understanding of the underlying mechanisms and developing effective ways to translate these insights into clinical practice remain significant challenges and unmet needs in the area. Several recent reviews have focused on mechanistic dissection of anesthetic-mediated cardioprotection. The present review focuses on recent clinical trials investigating the cardioprotective effects of anesthetics in the past five years. In addition to highlighting the main outcomes of these trials, the authors provide their perspectives about the current gap in the field and potential directions for future investigations.

Use of biopartitioning micellar chromatography and RP-HPLC for the determination of blood-brain barrier penetration of α-adrenergic/imidazoline receptor ligands, and QSPR analysis

For this study, 31 compounds, including 16 imidazoline/α-adrenergic receptor (IRs/α-ARs) ligands and 15 central nervous system (CNS) drugs, were characterized in terms of the retention factors (k) obtained using biopartitioning micellar and classical reversed phase chromatography (log k_BMC and log k_wRP, respectively). Based on the retention factor (log k_wRP) and slope of the linear curve (S) the isocratic parameter (φ₀) was calculated. Obtained retention factors were correlated with experimental log BB values for the group of examined compounds. High correlations were obtained between logarithm of biopartitioning micellar chromatography (BMC) retention factor and effective permeability (r(log k_BMC/log BB): 0.77), while for RP-HPLC system the correlations were lower (r(log k_wRP/log BB): 0.58; r(S/log BB): -0.50; r(φ₀/P_e): 0.61). Based on the log k_BMC retention data and calculated molecular parameters of the examined compounds, quantitative structure-permeability relationship (QSPR) models were developed using partial least squares, stepwise multiple linear regression, support vector machine and artificial neural network methodologies. A high degree of structural diversity of the analysed IRs/α-ARs ligands and CNS drugs provides wide applicability domain of the QSPR models for estimation of blood-brain barrier penetration of the related compounds.

New 2-Aminothiazoline derivatives lower blood pressure of spontaneously hypertensive rats (SHR) via I1-imidazoline and alpha-2 adrenergic receptors activation

2-Aminothiazolines share an isosteric relationship with imidazolines and oxazolines with antihypertensive activity mainly mediated by the imidazoline I₁-receptor. In the present work, we have prepared five aminothiazolines, following a previously described synthetic pathway. Aminothiazolines derived from dicyclopropylmethylamine (ATZ1) and cyclohexylamine (3) are unprecedented in the literature. Competitive radioligand assay was carried out with all synthetic compounds, and the I₁ receptor affinity in comparison to rilmenidine in PC12 cells was determined. Surprisingly, the rilmenidine isoster (ATZ1) showed no I₁-receptor interaction. Diethyl (ATZ4) and 2-ethyl-hexylamine (ATZ5) derivatives bind to the receptor with 11.98 and 10.94nmol/l, respectively. These compounds were selected for in vivo experiments. Both compounds reduced the blood pressure of spontaneously hypertensive rats (SHR). The hypotensive effect of these compounds was abrogated in the presence of α₂ adrenergic (yohimbine) and I₁ (efaroxan) receptor antagonists suggesting that both aminothiazolines bind to the adrenergic and imidazoline receptors. Lipinski's descriptors of the synthesized aminothiazolines were calculated and are similar to the known imidazoline I₁ receptor ligands. 3D-Similarity between ATZ5 and agmatine, the natural imidazoline receptor ligand, was also observed.

Transition metal and base free synthesis of 2-aryl-2-oxazolines from aldehydes and β-amino alcohols catalysed by potassium iodide

Synthesis of 2-aryl-2-oxazolines from β-amino alcohols and aldehydes was achieved in good to excellent yield by employing a potassium iodide (KI)–tert-butyl hydroperoxide (TBHP) catalytic system.

2-(3,4-Di-meth-oxy-phen-yl)-1-pentyl-4,5-diphenyl-1H-imidazole

The central imidazole ring in the title compound, C₂₈H₃₀N₂O₂, makes dihedral angles of 28.42 (13), 71.22 (15) and 29.50 (14)°, respectively, with the phenyl rings in the 4- and 5-positions and the 3,4-di­meth­oxy­phenyl group. In the crystal, mol­ecules are linked by C—H⋯O and C—H⋯N hydrogen bonds, weak π–π stacking inter­actions [centroid–centroid distance = 3.760 (2) Å] and C—H⋯π contacts, forming a three-dimensional network.

α(2) Adrenergic and imidazoline receptor agonists prevent cue-induced cocaine seeking

BACKGROUND

Drug-associated cues can elicit stress-like responses in addicted individuals, indicating that cue- and stress-induced drug relapse may share some neural mechanisms. It is unknown whether α(2) adrenergic receptor agonists, which are known to attenuate stress-induced reinstatement of drug seeking in rats, also reduce cue-induced reinstatement.

METHODS

Rats were tested for reinstatement of drug seeking following cocaine self-administration and extinction. We first evaluated the effects of clonidine, an agonist at α(2) and imidazoline-1 (I(1)) receptors, on relapse to cocaine seeking. To explore possible mechanisms of clonidine's effects, we then tested more specific α(2) or I(1) agonists, postsynaptic adrenergic receptor (α(1) and β) antagonists, and corticotropin-releasing factor receptor-1 antagonists.

RESULTS

We found that clonidine, and the more selective α(2) agonists UK-14,304 and guanfacine, decreased cue-induced reinstatement of cocaine seeking. The specific I(1) receptor agonist moxonidine reduced cue-induced as well as cocaine-induced reinstatement. Clonidine or moxonidine effects on cue-induced reinstatement were reversed by the selective α(2) receptor antagonist RS-79948, indicating a role for α(2) receptors. Prazosin and propranolol, antagonists at the α(1) and β receptor, respectively, reduced cue-induced reinstatement only when administered in combination. Finally, the corticotropin-releasing factor receptor-1 antagonist CP-154,526 reduced cue-induced reinstatement, as previously observed for stress-induced reinstatement, indicating possible overlap between stress and cue mechanisms.

CONCLUSIONS

These results indicate that α(2) and I(1) receptor agonists are novel therapeutic options for prevention of cue-induced cocaine relapse. Given that α(2) receptor stimulation is associated with sedation in humans, the I(1) agonist moxonidine seems to have substantial potential for treating addictive disorders.

Modulation of N-type calcium currents by presynaptic imidazoline receptor activation in rat superior cervical ganglion neurons

Presynaptic imidazoline receptors (R(i-pre)) are found in the sympathetic axon terminals of animal and human cardiovascular systems, and they regulate blood pressure by modulating the release of peripheral noradrenaline (NA). The cellular mechanism of R(i-pre)-induced inhibition of NA release is unknown. We, therefore, investigated the effect of R(i-pre) activation on voltage-dependent Ca(2+) channels in rat superior cervical ganglion (SCG) neurons, using the conventional whole-cell patch-clamp method. Cirazoline (30 μM), an R(i-pre) agonist as well as an α-adrenoceptor (R(α)) agonist, decreased Ca(2+) currents (I(Ca)) by about 50% in a voltage-dependent manner with prepulse facilitation. In the presence of low-dose rauwolscine (3 μM), which blocks the α(2)-adrenoceptor (R(α2)), cirazoline still inhibited I(Ca) by about 30%, but prepulse facilitation was significantly attenuated. This inhibitory action of cirazoline was almost completely prevented by high-dose rauwolscine (30 μM), which blocks R(i-pre) as well as R(α2). In addition, pretreatment with LY320135 (10 μM), another R(i-pre) antagonist, in combination with low-dose rauwolscine (3 μM), also blocked the R(α2)-resistant effect of cirazoline. Addition of guanosine-5-O-(2-thiodiphosphate) (2 mm) to the internal solutions significantly attenuated the action of cirazoline. However, pertussis toxin (500 ng ml(1)) did not significantly influence the inhibitory effect of cirazoline. Moreover, cirazoline (30 μM) suppressed M current in SCG neurons cultured overnight. Finally, omega-conotoxin (omega-CgTx) GVIA (1 μM) obstructed cirazoline-induced current inhibition, and cirazoline (30 μM) significantly decreased the frequency of action potential firing in a partly reversible manner. This cirazoline-induced inhibition of action potential firing was almost completely occluded in the presence of omega-CgTx. Taken together, our results suggest that activation of R(i-pre) in SCG neurons reduced N-type I(Ca) in a pertussis toxin- and voltage-insensitive pathway, and this inhibition attenuated repetitive action potential firing in SCG neurons.

Rilmenidine attenuates toxicity of polyglutamine expansions in a mouse model of Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a polyglutamine expansion in huntingtin. There are no treatments that are known to slow the neurodegeneration caused by this mutation. Mutant huntingtin causes disease via a toxic gain-of-function mechanism and has the propensity to aggregate and form intraneuronal inclusions. One therapeutic approach for HD is to enhance the degradation of the mutant protein. We have shown that this can be achieved by upregulating autophagy, using the drug rapamycin. In order to find safer ways of inducing autophagy for clinical purposes, we previously screened United States Food and Drug Administration-approved drugs for their autophagy-stimulating potential. This screen suggested that rilmenidine, a well tolerated, safe, centrally acting anti-hypertensive drug, could induce autophagy in cell culture via a pathway that was independent of the mammalian target of rapamycin. Here we have shown that rilmenidine induces autophagy in mice and in primary neuronal culture. Rilmenidine administration attenuated the signs of disease in a HD mouse model and reduced levels of the mutant huntingtin fragment. As rilmenidine has a long safety record and is designed for chronic use, our data suggests that it should be considered for the treatment of HD and related conditions.

1,3-Dibromo-5,5-dimethylhydantoin as an efficient homogeneous catalyst for the synthesis of 2-arylthiazolines and 2-arylimidazolines

A simple, facile, and efficient procedure for the synthesis of 2-arylthizolines and 2-arylimidazolines has been developed by the simple condensation of nitriles with 2-aminoethanethiol or ethylenediamine catalyzed by 1,3-dibromo-5,5-dimethylhydantoin under solvent-free conditions. Selective preparation of bisthiozolines and monoimidazolines from dinitriles and also selective conversion of arylnitriles to their corresponding 2-arylthiazolines or imidazolines in the presence of alkylnitriles can be considered as considerable advantages of this method.

G-protein inwardly rectifying potassium channels are involved in the hypotensive effect of I1-imidazoline receptor selective ligands

OBJECTIVE

The present study examined the role of G-protein inwardly rectifying potassium (GIRK) channels in the depressor responses elicited by intracisternal injections of imidazoline-like drugs in anesthetized rabbits.

METHODS AND RESULTS

Intracisternal injections of the I1-imidazoline receptor (I1R) selective ligands LNP509 (30 microg/kg) and LNP640 (2 microg/kg) (subthreshold doses), and of the GIRK channel opener flupirtine (30 microg/kg) did not affect mean arterial blood pressure (MAP). LNP509 and LNP640, however, elicited substantial depressor responses in rabbits pretreated with flupirtine (-17 +/- 2 and -18 +/- 1 mmHg, respectively, P < 0.05). Injection of higher doses of LNP509 (200 microg/kg) or LNP640 (10 microg/kg) elicited substantial reductions in MAP (-45 +/- 3 and -39 +/- 2 mmHg, respectively, P < 0.05) in naive rabbits. The depressor responses elicited by the higher doses of LNP509 or LNP640 were markedly diminished by pretreatment with the GIRK channel blocker tertiapin-Q (10 microg/kg) (-23 +/- 3 and -26 +/- 2 mmHg, respectively, P < 0.05 compared with nonpretreated rabbits), whereas tertiapin-Q (10 microg/kg) did not affect MAP by itself. Maximal-specific binding (Bmax) of the I1R ligand [I]LNP911 to PC12 cell membranes (296 +/- 59 fmol/mg protein) was enhanced by flupirtine pretreatment whereas it was reduced by tertiapin-Q pretreatment (687 +/- 122 and 68 +/- 21 fmol/mg protein, respectively, P < 0.05 vs. control binding).

CONCLUSION

These findings demonstrate that the modulation of GIRK channels affects I1R's function and raise the possibility that GIRK channels, and I1Rs are parts of a single proteic complex.

Therapeutic use of release-modifying drugs

Presynaptic inhibitory or facilitatory autoreceptors are targets for the endogenous neurotransmitter of the respective neuron, and also for exogenous agonists, partial agonists and antagonists which can produce pharmacological actions through changes in transmitter release. In addition, presynaptic inhibitory or facilitatory heteroreceptors can also be acted upon by exogenous agonists, partial agonists or antagonists to induce changes in transmitter release with useful therapeutic effects. This article summarizes drugs that are known or likely to produce their therapeutic effects through presynaptic modulation of neurotransmitter release. Included are drugs acting on alpha and beta adrenoceptors, dopamine receptors, angiotensin, opioid, cannabinoid, and nicotinic acetylcholine receptors. Also discussed are changes in presynaptic receptor mechanisms produced by drugs that inhibit transmitter re-uptake.

A Resource-Efficient and Highly Flexible Procedure for a Three-Component Synthesis of 2-Imidazolines

A multicomponent reaction between alpha-acidic isonitriles, primary amines, and carbonyl compounds was studied using 14 different solvents. Depending on the isocyanide that was used, optimal yields for the three-component synthesis of 2H-2-imidazolines were observed in different solvents. The solvents could be used as purchased, and in situ preformation of the imine was not required. By selecting the appropriate solvent, it was possible to considerably expand the range of compatible isocyanides toward less alpha-acidic isocyanides. Further process simplification was achieved by performing the reaction at higher concentrations and avoiding purification by column chromatography, resulting in a fast, easy to perform, and resource-efficient protocol for this three-component reaction.

Reduced Hemodynamic Responses to Physical and Mental Stress Under Low-Dose Rilmenidine in Healthy Subjects

Activation of the sympathetic nervous system plays a major role in the pathogenesis and prognosis of cardiovascular diseases. Rilmenidine is an I(1)-imidazoline receptor agonist that reduces blood pressure by modulation of central sympathetic activity, but the effects of low-dose rilmenidine on the hemodynamic responses to physiological maneuvers that increase adrenergic drive is not known. To assess the effects of low-dose rilmenidine on the hemodynamic responses to stress, 32 healthy subjects (20-56 years old) underwent acute physical exercise (n = 15, individualized ramp protocol on treadmill) and mental stress (n = 17, word color Stroop and mental arithmetics tests) two hours after the oral administration of 0.5 mg of rilmenidine (RIL) or placebo (PLA) following a randomized, double-blind, placebo controlled crossover study. No subject complained of any side effect. Rilmenidine reduced peak exercise heart rate (PLA: 187 +/- 7; RIL: 181 +/- 9 bpm; P = 0.003), but did not modify peak aerobic power (VO(2max) - PLA: 41.7 +/- 6.2; RIL: 42.3 +/- 6.7 ml/kg/min; P = 0.26). During mental stress, rilmenidine inhibited the peak systolic (PLA: 123 +/- 10; RIL: 114 +/- 8 mmHg; P = 0.02) and diastolic (PLA: 86 +/- 7; RIL: 81 +/- 7 mmHg; P <0.05) blood pressure responses. In conclusion, rilmenidine reduced the hemodynamic response to physical and mental stress stimuli without limiting exercise capacity. These results support the concept that rilmenidine, at a dose lower than the ones recommended to treat hypertension, reduced the myocardial oxygen demand to stress and may carry potential clinical impact.

Silylmethyl-substituted aziridine and azetidine as masked 1,3- and 1,4-dipoles for formal [3 + 2] and [4 + 2] cycloaddition reactions

2-tert-Butyldiphenylsilylmethyl-substituted aziridine and the corresponding azetidine reacted efficiently with nitriles and carbonyl substrates to generate imidazoline, oxazolidine, and tetrahydropyrimidine products. The azetidine rearranged efficiently to the pyrrolidine skeleton involving migration of silicon under BF3.Et2O conditions. The tert-butyldiphenylsilylmethyl function, latent to CH2OH group, controlled not only the regioselectivity of aziridine and azetidine cleavage but also the relative stereochemistry of the substituents in the products derived from substituted aziridine.

Diastereochemical Diversity of Imidazoline Scaffolds via Substrate Controlled TMSCl Mediated Cycloaddition of Azlactones

[reaction: see text] We report herein a trimethylsilyl chloride mediated substrate controlled 1,3-dipolar cycloaddition for the diastereoselective synthesis of either syn- or anti-imidazolines. This method provides scaffolds with four points of diversity and control over two stereocenters.

Neuronal Norepinephrine Responses of the Rostral Ventrolateral Medulla and Nucleus Tractus Solitarius Neurons Distinguish the I1- from the α2-Receptor-Mediated Hypotension in Conscious SHRs

We tested the hypothesis that the I1 receptor mediates the reduction in rostral ventrolateral medulla (RVLM) neuronal norepinephrine (NE; index of sympathetic activity) that leads to hypotension independent of other brainstem areas or the alpha2-adrenergic receptor. To this end, we developed a model that permitted measurement of real-time changes in neuronal NE in the RVLM or nucleus tractus solitarius (NTS) along with blood pressure and heart rate in the conscious SHR in response to localized microinjections of selective I1 (rilmenidine) or alpha2-adrenergic (alpha-methylnorepinephrine; alpha-MNE) agonist versus the mixed I1/alpha2 agonist clonidine. To further support the hypothesis, we investigated the effects of localized selective alpha2- (SK&F86466) or I1 (efaroxan) blockade on the reductions in neuronal NE and blood pressure elicited by intra-RVLM rilmenidine. In the latter experiment, changes in RVLM neuronal c-Fos (another marker of sympathetic neural activity) were also investigated. Intra-RVLM rilmenidine (40 nmol) or clonidine (1 nmol) similarly reduced RVLM NE and blood pressure; these responses were approximately 2-fold greater than those elicited by the pure alpha2-adrenergic agonist alpha-MNE (10 nmol). By contrast, intra-NTS rilmenidine or clonidine had no effect on NTS NE or blood pressure versus significant reductions in both parameters by alpha-MNE. Intra-RVLM rilmenidine decreased c-Fos expression, and these responses were abolished by efaroxan but not by SK&F 86466. These findings suggest: (1) in the RVLM, I1-receptor signaling suppresses cardiovascular neuron activity, which leads to lowering of blood pressure; (2) although the alpha2-adrenergic receptor in the RVLM serves a similar role, it does not exert a tonic neuronal inhibitory effect and is not essential, as a downstream signaling entity, for the I1-evoked neurobiological effects in the brainstem. The potential confounding effects of anesthetics on the I1 and/or alpha2 receptor-mediated neuronal and cardiovascular responses were circumvented in the present study.

The imidazoline-like drug S23515 affects lipid metabolism in hepatocyte by inhibiting the oxidosqualene: lanosterol cyclase activity

Imidazoline-like drugs are centrally-acting antihypertensive agents that inhibit the activity of the sympathetic nervous system by interacting with the alpha2-adrenoreceptor and also with a non-adrenergic imidazoline binding site called the imidazoline 1 receptor. Recently, these molecules were proposed to play an additional role in cardiovascular diseases by acting on glucose and lipid metabolism. We used S23515, a potent imidazoline-like molecule acting selectively on blood pressure through the imidazoline 1 receptor, to decipher the effects of these drugs on lipid metabolism. We found that S23515 inhibited specifically and dose-dependently cholesterol synthesis in cultured rodent and primate hepatocytes. This hypocholesterolemic effect was likely due to the inhibition of the oxido:lanosterol cyclase (OSC), a rate-limiting enzyme in the cholesterol biosynthetic pathway. Partial OSC inhibition induced by S23515 led to the generation of 24(S),25-epoxycholesterol, a potent ligand for the liver X receptor (LXR). Furthermore, S23515 increased in human macrophages the expression of both ABCA1 and G1, the 2 ATP binding cassette transporters, which play a pivotal role in the reverse cholesterol transport. Thus, these results suggest that S23515, and potentially other imidazoline-like drugs, could exert hypolipidemic effects in addition to their hypotensive activities.

Multicomponent Synthesis of 2-Imidazolines

[reaction: see text] A multicomponent reaction (MCR) between amines, aldehydes, and isocyanides bearing an acidic alpha-proton gives easy access to a diverse range of highly substituted 2-imidazolines. The limitations of the methodology seem to be determined by the reactivity of the isocyanide and by the steric bulk on the in situ generated imine rather than by the presence of additional functional groups on the imine. Less reactive isocyanides, for example p-nitrobenzyl isocyanide 25a, react successfully with amines and aldehydes, using a catalytic amount of silver(I) acetate. Some of the resulting p-nitrophenyl-substituted 2-imidazolines undergo air oxidation to the corresponding imidazoles. Differences in reactivity of the employed isocyanides are explained with use of DFT calculations. Difficult reactions with ketones instead of aldehydes as the oxo-compound in this MCR are promoted by silver(I) acetate as well.

Cardiovascular and survival effects of sympatho-inhibitors in adriamycin-induced cardiomyopathy in rats

Adriamycin (ADR) is a widely used drug for the treatments of cancers. This study evaluates the effects of moxonidine and metoprolol on cardiac hemodynamics and survival in ADR-induced left ventricular dysfunction (total dose of 20 mg/kg in a 4-week regimen). Rats were treated with the centrally acting I(1)R agonist sympatho-inhibitor, moxonidine, or with the non-selective beta-adrenergic antagonist, metoprolol, during 1 month or until death. Treatments began 1 week after the onset of the ADR administration. Low doses (0.5 and 1 mg/kg/day) of moxonidine and metoprolol (10 mg/kg/day) improved cardiovascular function. High doses of moxonidine (3 mg/kg/day) and metoprolol (150 mg/kg/day) were cardiodepressive. Moxonidine and metoprolol both failed to improve survival. These data indicate that a treatment with these sympatho-inhibitors can reduce the left ventricular dysfunction induced by ADR. Moreover, these cardioprotective effects where obtained even when ADR was used at a dose regimen usually employed for its antineoplastic effects in rodents. Nevertheless, in this particular cardiomyopathy, we did not find any association between improvements of functional parameters and survival whatever the drug and the dose used. This problem points out the difficulty to prevent, at least with sympatho-inhibitory drugs alone, the mortality linked to the chronic cardiotoxicity of ADR.

LNP 906, the first high-affinity photoaffinity ligand selective for I1 imidazoline receptors

1 The hypotensive effect of imidazoline-like drugs, such as clonidine, was attributed both to alpha2-adrenergic receptors and nonadrenergic imidazoline receptors, which are divided into I1, I2 and I3 subtypes. 2 We have recently synthesized a derivative of (2-(2-chloro-4-iodo-phenylamino)-5-methyl-pyrroline (LNP 911), the first high-affinity and selective ligand for I1 receptors (I1R), with a photoactivable function (LNP 906). 3 This work aims to test whether this derivative retained the binding properties of LNP 911 and bound irreversibly to I1R. 4 Binding studies showed that LNP 906 exhibited nanomolar affinity for I1R and was selective for I1R over I2 receptors and alpha2-adrenergic receptors (alpha2Ars). 5 Upon exposure to u.v. light, LNP 906 irreversibly blocked the binding of [125I]-paraiodoclonidine (PIC) to I1R, time- and dose-dependently, on PC12 cell membranes and interacted with I1R in a reversible and competitive manner in the absence of light. Pharmacological studies showed that this blockade was prevented by the concomitant presence of rilmenidine (a well-known I1 agonist), but not by rauwolscine (an alpha2 antagonist). 6 Finally, LNP 906 clearly antagonized the decrease in forskolin-stimulated cAMP level induced by rilmenidine, but not by melatonin. 7 These results indicate that LNP 906 is the first high-affinity and selective photoaffinity ligand for I1R and that it behaves as an I1R antagonist.

Highly efficient enantiospecific synthesis of imidazoline-containing amino acids using bis(triphenyl)oxodiphosphonium trifluoromethanesulfonate

A highly efficient enantiospecific synthesis of imidazoline-based amino acids is reported from dipeptides composed of a C-terminal beta-amino-alpha-amino acid residue using bis(triphenyl) oxodiphosphonium trifluoromethanesulfonate. These imidazolines were easily converted to imidazoles and incorporated into macrolactam analogues of bistratamide H without loss of stereochemical integrity.

Comparison of rilmenidine and lisinopril on ambulatory blood pressure and plasma lipid and glucose levels in hypertensive women with metabolic syndrome

OBJECTIVE

In previous studies, the I1 imidazoline specific agonist rilmenidine effectively lowered office blood pressure (BP) in patients with metabolic syndrome, improved glucose metabolism and did not demonstrate unfavourable effects on plasma lipids. The aim of the present study was to investigate the effects of 12weeks therapy with rilmenidine compared with the ACE inhibitor lisinopril on ambulatory BP, plasma lipid and fasting glucose levels in women with metabolic syndrome.

RESEARCH DESIGN

Prospective randomised open-label, blinded end-points study.

METHODS

Female patients (n = 51) with hypertension and other components of metabolic syndrome were treated with 1 mg rilmenidine (n = 24) or 10 mg lisinopril (n = 27), once- or twice-daily. Anthropometric measurements, office BP and heart rate (HR) measurements, ambulatory BP monitoring, lipid and fasting glucose assessment were performed before and after 12weeks of treatment

MAIN OUTCOME MEASURES

Changes in ambulatory BP and HR, including 24-h, daytime and night-time values, and in lipids and glucose levels. All changes were adjusted for baseline values using the analysis of covariance method.

RESULTS

Ambulatory 24-h systolic BP and diastolic BP were decreased significantly in the rilmenidine group (-11.9 +/- 1.9 and -7.7 +/- 0.8 mm Hg, p < 0.001) respectively and the lisinopril group (-11.0 +/- 1.8 and -6.7 +/- 0.7 mm Hg respectively, p < 0.001). There were no significant differences between the two groups. Rilmenidine reduced 24-h ambulatory HR (-3.6 +/- 0.8 bpm versus 0.3 +/- 0.8 bpm with lisinopril; p = 0.002). The reductions of day-time and night-time BP were also significant for both treatment groups, but the rilmenidine group demonstrated a greater decrease in night-time diastolic BP (p = 0.046). Rilmenidine significantly increased HDL cholesterol and decreased fasting glucose levels (p = 0.009 and p = 0.012, respectively). HDL cholesterol tended to increase and fasting glucose tended to decrease in the lisinopril group. However, differences between groups were not significant.

CONCLUSION

Rilmenidine has similar effects on ambulatory BP patterns in hypertensive women with metabolic syndrome as lisinopril. Rilmenidine compared with lisinopril significantly reduces ambulatory HR. In this study, rilmenidine and lisinopril demonstrate similar effects on plasma lipid and fasting glucose levels.