1-[(Imidazolidin-2-yl)imino]indazole. Highly α2/I1 Selective Agonist: Synthesis, X-ray Structure, and Biological Activity

Synthesis and Photophysical Properties of 3-Substituted-1H-Indazoles: A Pd-Catalyzed Double C-N Bond Formation Strategy via 1,6-Conjugate Addition

A Pd-catalyzed cascade process for the direct synthesis of 3-substituted-1H-indazole employing p-quinone methide (p-QM) and arylhydrazine through Pd-catalyzed double C-N bond formation via 1,6-conjugate addition is reported. This reaction strategy affords efficient and practical access to synthetically important diverse 3-substituted-1H-indazoles in good yields. The photophysical properties of the synthesized 3-substituted-1H-indazoles are investigated, and some of them showed very good fluorescence properties with quantum yields up to 85%. Also, the synthesized 3-substituted-1H-indazole exhibits an acid-sensitive fluorescence turn-off activity.

A Molecular Toolbox of Positron Emission Tomography Tracers for General Anesthesia Mechanism Research

With appropriate radiotracers, positron emission tomography (PET) allows direct or indirect monitoring of the spatial and temporal distribution of anesthetics, neurotransmitters, and biomarkers, making it an indispensable tool for studying the general anesthesia mechanism. In this Perspective, PET tracers that have been recruited in general anesthesia research are introduced in the following order: 1) ¹¹C/¹⁸F-labeled anesthetics, i.e., PET tracers made from inhaled and intravenous anesthetics; 2) PET tracers targeting anesthesia-related receptors, e.g., neurotransmitters and voltage-gated ion channels; and 3) PET tracers for studying anesthesia-related neurophysiological effects and neurotoxicity. The radiosynthesis, pharmacodynamics, and pharmacokinetics of the above PET tracers are mainly discussed to provide a practical molecular toolbox for radiochemists, anesthesiologists, and those who are interested in general anesthesia.

Quaternary Ru(II) complexes of terpyridines, saccharin and 1,2-azoles: effect of substituents on molecular structure, speciation, photoactivity, and photocytotoxicity

Six photoactive ruthenium quaternary complexes (a four-component system consisting of three different N-donor ligands and Ru(II)): trans-[Ru(R-tpy)(pyz/ind)(sac)₂] (1-6) containing substituted terpyridine (R-tpy), saccharin (sac), and monodentate N-donor heterocycles were designed. Here, R-tpy = 4'-(2-furyl (1, 2); thienyl (3, 4); pyridyl (5, 6))-2,2':6',2'' terpyridines, pyz = 1H-pyrazole for 1, 3 and 5 and ind = 1H-indazole for 2, 4 and 6. The azoles are present in a large number of FDA-approved clinical drugs and bioactive molecules. The saccharin acting as a carbonic anhydrase inhibitor (CA-IX) could potentially target aggressive hypoxic tumors that overexpress CA-IX. Such multi-functional ligands bound to a Ru(II)-photocage provide ample scope to tune the electronic structures, photochemistry, and synergistic effect of the photolabile ligands in photoactivated chemotherapy (PACT). The complexes were characterized using various spectroscopic studies, and the molecular structures were determined from X-ray crystallography. They exhibit a distorted octahedral {RuN₆} geometry with equatorial sites coordinated to the tridentate N₃-donor R-tpy and N-donor pyz/ind, while two transoidal axial sites bound to the N-donor saccharinate (sac) ligands. The solvolysis kinetics showed these complexes undergo facile ligand-exchange reactions in equilibrium with varying rates reflecting the possible electronic effect of the R-groups in R-tpy. The photoreactivity of the complexes in green (λ_ex = 530 nm) LED light indicates that the complexes undergo photodissociation of the monodentate N-donors (i.e., sac/pyz/ind) and showed an efficient generation of singlet oxygen (Φ_1O2 = 0.29-0.47), signifying the potential of these complexes in PACT and/or PDT. All the complexes show good binding affinity with CT-DNA with possible intercalation from extended planar polypyridyl ligands with duplex DNA and BSA. The synchronous fluorescence study with BSA suggested preferential interaction at the tryptophan residue in the protein microenvironment. The confocal microscopy studies showed adequate permeability and localization in the cytosol and nucleus of cervical cancer (HeLa) and breast cancer (MCF7) cells. The dose-dependent cytotoxicity of the complexes for both HeLa and MCF7 cells increases upon low-energy (365 nm) photoirradiation. The mechanistic studies revealed that the complexes induce apoptosis and generate reactive oxygen species (ROS) upon green light (λ_ex = 530 nm) irradiation. Overall, these quaternary Ru(II) complexes equipped with three different types of ligands with distinct roles could pave the way for designing multi-targeted chemotherapeutic metallodrugs with synergistic roles for each bioactive ligand.

Indazole and its Derivatives in Cardiovascular Diseases: Overview, Current Scenario, and Future Perspectives

Indazoles are a class of heterocyclic compounds with a bicyclic ring structure composed of a pyrazole ring and a benzene ring. Indazole-containing compounds with various functional groups have important pharmacological activities and can be used as structural motifs in designing novel drug molecules. Some of the indazole-containing molecules are approved by FDA and are already in the market. However, very few drugs with indazole rings have been developed against cardiovascular diseases. This review aims to summarize the structural and pharmacological functions of indazole derivatives which have shown efficacy against cardiovascular pathologies in experimental settings.

Synthesis of the Guanidine Derivative: N-{[(7-(4,5-Dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)amino](phenylamino)methylene}benzamide

The guanidine derivative N-{[(7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene)amino](phenylamino)methylene}benzamide (3) has been obtained by the reaction of one measure of N-{[7-(4,5-dihydro-1H-imidazol-2-yl)-2-(p-tolyl)-6,7-dihydro-2H-imidazo[2,1-c][1,2,4]triazol-3(5H)-ylidene]carbamothioyl}benzamide (2) with one measure of aniline in the presence of mercury(II) chloride and triethylamine in anhydrous dimethylformamide. The structure of product 3 was confirmed by 1H and 13C-NMR, infrared spectroscopy, and elemental analysis.

PET Radiotracers for CNS-Adrenergic Receptors: Developments and Perspectives

Epinephrine (E) and norepinephrine (NE) play diverse roles in our body’s physiology. In addition to their role in the peripheral nervous system (PNS), E/NE systems including their receptors are critical to the central nervous system (CNS) and to mental health. Various antipsychotics, antidepressants, and psychostimulants exert their influence partially through different subtypes of adrenergic receptors (ARs). Despite the potential of pharmacological applications and long history of research related to E/NE systems, research efforts to identify the roles of ARs in the human brain taking advantage of imaging have been limited by the lack of subtype specific ligands for ARs and brain penetrability issues. This review provides an overview of the development of positron emission tomography (PET) radiotracers for in vivo imaging of AR system in the brain.

Radiosynthesis and Preclinical Evaluation of an α2A-Adrenoceptor Tracer Candidate, 6-[18F]Fluoro-marsanidine

PURPOSE

The α₂-adrenoceptors mediate many effects of norepinephrine and epinephrine, and participate in the regulation of neuronal, endocrine, cardiovascular, vegetative, and metabolic functions. Of the three receptor subtypes, only α_2A and α_2C are found in the brain in significant amounts. Subtype-selective positron emission tomography (PET) imaging of α₂-adrenoceptors has been limited to the α_2C subtype. Here, we report the synthesis of 6-[¹⁸F]fluoro-marsanidine, a subtype-selective PET tracer candidate for α_2A-adrenoceptors, and its preclinical evaluation in rats and mice.

PROCEDURES

6-[¹⁸F]Fluoro-marsanidine was synthesized using electrophilic F-18 fluorination with [¹⁸F]Selectfluor bis(triflate). The tracer was evaluated in Sprague Dawley rats and in α_2A-knockout (KO) and wild-type (WT) mice for subtype selectivity. In vivo PET imaging and ex vivo brain autoradiography were performed to determine the tracer distribution in the brain. The specificity of the tracer for the target was determined by pretreatment with the subtype-non-selective α₂-agonist medetomidine. The peripheral biodistribution and extent of metabolism of 6-[¹⁸F]fluoro-marsanidine were also analyzed.

RESULTS

6-[¹⁸F]Fluoro-marsanidine was synthesized with [¹⁸F]Selectfluor bis(triflate) in a radiochemical yield of 6.4 ± 1.7 %. The molar activity was 3.1 to 26.6 GBq/μmol, and the radiochemical purity was > 99 %. In vivo studies in mice revealed lower uptake in the brains of α_2A-KO mice compared to WT mice. The results for selectivity were confirmed by ex vivo brain autoradiography. Blocking studies revealed reduced uptake in α_2A-adrenoceptor-rich brain regions in pretreated animals, demonstrating the specificity of the tracer. Metabolite analyses revealed very rapid metabolism of 6-[¹⁸F]fluoro-marsanidine with blood-brain barrier-permeable metabolites in both rats and mice.

CONCLUSION

6-[¹⁸F]Fluoro-marsanidine was synthesized and evaluated as a PET tracer candidate for brain α_2A-adrenoceptors. However, rapid metabolism, extensive presence of labeled metabolites in the brain, and high non-specific uptake in mouse and rat brain make 6-[¹⁸F]fluoro-marsanidine unsuitable for α_2A-adrenoceptor targeting in rodents in vivo.

Cardiovascular Effects Mediated by Imidazoline Drugs: An Update

OBJECTIVE

Clonidine is a centrally acting antihypertensive drug. Hypotensive effect of clonidine is mediated mainly by central α2-adrenoceptors and/or imidazoline receptors located in a complex network of the brainstem. Unfortunately, clonidine produces side effects such as sedation, mouth dry, and depression. Moxonidine and rilmenidine, compounds of the second generation of imidazoline drugs, with fewer side effects, display a higher affinity for the imidazoline receptors compared with α2-adrenoceptors. The antihypertensive action of these drugs is due to inhibition of the sympathetic outflow primarily through central I1-imidazoline receptors in the RVLM, although others anatomical sites and mechanisms/receptors are involved. Agmatine is regarded as the endogenous ligand for imidazoline receptors. This amine modulates the cardiovascular function. Indeed, when administered in the RVLM mimics the hypotension of clonidine.

RESULTS

Recent findings have shown that imidazoline drugs also exert biological response directly on the cardiovascular tissues, which can contribute to their antihypertensive response. Currently, new imidazoline receptors ligands are in development.

CONCLUSION

In the present review, we provide a brief update on the cardiovascular effects of clonidine, moxonidine, rilmenidine, and the novel imidazoline agents since representing an important therapeutic target for some cardiovascular diseases.

Recent Advances in the Development of Indazole-based Anticancer Agents

Cancer is one of the leading causes of human mortality globally; therefore, intensive efforts have been made to seek new active drugs with improved anticancer efficacy. Indazole-containing derivatives are endowed with a broad range of biological properties, including anti-inflammatory, antimicrobial, anti-HIV, antihypertensive, and anticancer activities. In recent years, the development of anticancer drugs has given rise to a wide range of indazole derivatives, some of which exhibit outstanding activity against various tumor types. The aim of this review is to outline recent developments concerning the anticancer activity of indazole derivatives, as well as to summarize the design strategies and structure-activity relationships of these compounds.

Are Alpha-2D Adrenoceptor Subtypes Involved in Rat Mydriasis Evoked by New Imidazoline Derivatives: Marsanidine and 7-Methylmarsanidine?

The imidazoline compounds may produce mydriasis after systemic administration to some species (rats, cats, and mice). In mydriatic activity of imidazolines, α_2D-adrenoceptors subtype(s) seems to be involved. In this study, the pupil dilatory effect evoked by 2 newly synthesized imidazoline derivatives—α₂-adrenoceptor agonists: marsanidine and 7-methylmarsanidine—was compared. The compounds were tested alone as well as in the presence of α₂-adrenoceptor antagonists (nonselective, yohimbine, and selective toward the following α₂-adrenoceptor subtypes—α_2A-2-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-2,3-dihydro-1-methyl-1H-isoindole maleate (BRL44408), α_2B-2-[2-(4-(2-methoxyphenyl)piperazin-1-yl)ethyl]-4,4-dimethyl-1,3-(2H,4H)-isoquinolindione dihydrochloride (ARC239), α_2C-JP1302, α_2D-2-(2,3-dihydro-2-methoxy-1,4-benzodioxin-2-yl)-4,5-dihydro-1H-imidazole hydrochloride [RX821002]). The agonists were studied in male Wistar rats and were administered intravenously in cumulative doses. The antagonistic compounds were given in a single dose before the experiment with marsanidine or 7-methylmarsanidine. Pupil diameter was measured with stereoscopic microscope equipped in green light filter. Marsanidine and 7-methylmarsanidine exerted marked mydriatic effects. BRL44408, JP1302, and ARC239 did not cause significant parallel shift to the right of the dose–effect curves obtained for both imidazolines. In case of yohimbine and RX821002, the marked parallel shifts of dose–response curves were observed, with the antagonistic effects of RX821002 more pronounced. In vivo pharmacodynamics experiment suggests that α_2D-adrenoceptor subtype is mainly engaged in mydriatic effects evoked in rats by imidazoline derivatives, in particular by clonidine.

Circulatory effect of TCS-80, a new imidazoline compound, in rats

BACKGROUND

Synthesis and hypotensive properties of centrally acting imidazoline agents: 1-[(imidazolidin-2-yl)imino]-1H-indazole (Marsanidine) and 7-chloro-1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (TCS-80) were tested in rats. We have recently synthesized two novel Marsanidine analogues which decrease blood pressure and heart rate in rats: 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indole (TCS-54), and 7-chloro-1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indole (TCS-213). Among all these analogues, compound TCS-80 exhibits the highest affinity to I1-imidazoline receptors and the lowest α2/I1 selectivity ratio. The observed cardiovascular effects of the compounds might be mediated through α2-adrenergic and I1-imidazoline receptors and subsequent decrease of the symphathetic nerve activity. The present studies were performed to determine whether α2-adrenergic and/or I1-imidazoline receptors are involved in the decrease of blood pressure and heart rate induced by Marsanidine, TCS-54, TCS-80, and TCS-213 in rats.

METHODS

Anesthetized rats were infused iv with the tested compounds and selective α2-adrenoceptor antagonist, RX821002, or nonselective α2-adrenergic/I1-imidazoline receptor antagonist, Efaroxan. The mean arterial blood pressure and heart rate were monitored directly and continuously throughout the experiment.

RESULTS

Efaroxan inhibited the hypotensive effect of TCS-80 stronger than RX821002. The degree of inhibition of the hypotensive effect of the remaining compounds was similar for both antagonists. The presence of Efaroxan and RX821002 diminished the heart rate decrease induced by all compounds administration, though the influence on the maximal chronotropic effect was attenuated significantly in the TCS-80 and TCS-213 treated animals only.

CONCLUSION

Our results indicate that hypotensive and negative chronotropic activities of all tested compounds are mediated by both the α2-adrenergic and I1-imidazoline receptors. Moreover, the circulatory effect of TCS-80 might be mediated to relatively higher degree by the I1-imidazoline receptors than by the α2-adrenergic ones.

Fluorinated analogues of marsanidine, a highly α2-AR/imidazoline I1 binding site-selective hypotensive agent. Synthesis and biological activities

The aim of these studies was to establish the influence of fluorination of the indazole ring on the pharmacological properties of two selective α2-adrenoceptor (α2-AR) agonists: 1-[(imidazolidin-2-yl)imino]-1H-indazole (marsanidine, A) and its methylene analogue 1-[(4,5-dihydro-1H-imidazol-2-yl)methyl]-1H-indazole (B). Introduction of fluorine into the indazole ring of A and B reduced both binding affinity and α2-AR/I1 imidazoline binding site selectivity. The most α2-AR-selective ligands were 6-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6c) and 7-fluoro-1-[(imidazolidin-2-yl)imino]-1H-indazole (6d). The in vivo cardiovascular properties of fluorinated derivatives of A and B revealed that in both cases the C-7 fluorination leads to compounds with the highest hypotensive and bradycardic activities. The α2-AR partial agonist 6c was prepared as a potential lead compound for development of a radiotracer for PET imaging of brain α2-ARs.

Vagotomy reveals the importance of the imidazoline receptors in the cardiovascular effects of marsanidine and 7-ME-marsanidine in rats

BACKGROUND

The recently synthesized novel benzazole derivates - marsanidine (1-[(imidazolidin-2-yl)imino]indazole) and 7-Me-marsanidine (1-[(imidazolidin-2-yl)imino]-7-methylindazole) display promising effects on the circulatory system. We previously indicated that i.v. administration of both compounds decreased the mean arterial blood pressure (MAP) and heart rate (HR) in rats. The cardiovascular effect of the tested compounds may consist not only in inhibiting the sympathetic, but also in activating the parasympathetic pathways related to vagal nerves. Present experiments were performed to determine how vagotomy, with or without an α2 adrenoreceptor blockade, may affect hypotensive and HR limiting actions of marsanidine and 7-Me-marsanidine.

METHODS

Both compounds were infused i.v. (10 μg/kg b.w.) to anesthetized rats, half of which underwent vagotomy. Half the intact, and half the vagotomised rats received RX821002, an α2 adrenorereceptor inhibitor. MAP and HR were monitored directly throughout the experiment.

RESULTS

Vagotomy enhanced hypotension observed after marsanidine administration. The α2 adrenergic blockade abolished the action of marsanidine in both the intact and vagotomised rats. Vagotomy did not affect the 7-Me-marsanidine-induced decrease of MAP or HR. However, it abolished the reducing effect of the α2 adrenergic receptor blockade on the hypotension triggered by 7-Me-marsanidine.

CONCLUSION

The results show that although cardiovascular effects of marsanidine and 7-Me-marsanidine are not mediated by the vagal nerves, vagotomy enhanced sensitivity of the sympathetic pathways for the tested compounds. While the action of marsanidine in vagotomised and intact rats may be explained by activation of the α2 adrenoreceptors, the effects of 7-Me-marsanidine seem to be α2 adrenoreceptor-independent. It seems likely that activation of I1 imidazoline receptors could mediate the observed effects.

Antitumor, antioxidant and antimicrobial studies of substituted pyridylguanidines

A series of N-pivaloyl-N′-(alkyl/aryl)-N″-pyridylguanidine of general formula C₄H₉CONHC(NR¹R²)NPy have been synthesized and characterized using elemental analysis, FT-IR, multinuclear NMR spectroscopy, and in the case of compounds 7 and 11, by single crystal X-ray diffraction (XRD). The synthesized guanidines were tested for antitumor activities against potato tumor, and showed excellent inhibition against Agrobacterium tumefaciens (AT10)-induced tumor. The antioxidant and antimicrobial activities of these new compounds against various bacterial and fungal strains were also investigated.

1-Allyl-6-nitro-1H-indazole

The fused five- and six-membered rings in the title mol-ecule, C10H9N3O2, are essentially coplanar, the largest deviation from the mean plane being 0.012 (1) Å for the C atom linked to the nitro group. The fused-ring system makes a dihedral angle of 11.34 (6)° with the nitro group, leading to a syn-periplanar conformation. The plane through the atoms forming the allyl group is nearly perpendicular to the indazole fused-ring system, as indicated by the dihedral angle of 73.3 (5)°. In the crystal, each mol-ecule is linked to its symmetry equivalent about the center of inversion by pairs of non-classical C-H⋯O hydrogen bonds, forming an extended tape motif parallel to the (-12-1) plane.

N-(Imidazolidin-2-ylidene)-1-arylmethanamine oxides: synthesis, structure and pharmacological evaluation

A high yielding three-step procedure was applied for the synthesis of N-(imidazolidin-2-ylidene)-1-arylmethanamine oxides 3 (α-aminonitrones) starting from the easily accessible imidazolidin-2-one O-benzyl oxime 1. The α-aminonitrone-α-iminohydroxyloamine tautomerism of these products was studied theoretically and the structures of the synthesised compounds were confirmed by single crystal X-ray crystallographic analysis. The compounds were evaluated in vitro for their binding affinities to α(1) and α(2) adrenoceptors as well as imidazoline I(1) and I(2) receptors. The highest potencies at the α(2) adrenergic receptors were observed for compounds bearing biphenyl (4h, K(i)  = 9 nM) and naphthyl (4i, K(i)  = 92 nM) moieties. Compounds 4h and 4i were further tested in vivo for their cardiovascular and sedative-hypnotic effects in rats.