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At least 109 records · Page 6Linked to original sources
PubMed1981

Isolation and identification of impurities in 4-acetyl-2-(2'-hydroxyethyl)5,6-bis(4-chlorophenyl)-2H-pyridazin-3-one, an antihypertensive agent.

Three trace impurities found in 4-acetyl-2-(2'-hydroxyethyl)-5,6-bis(4-chlorophenyl)-2H-pyridazin-3-one (II), a novel antihypertensive agent, were isolated by a combination of low-pressure liquid chromatography and preparative TLC. These impurities were identified as the formate ester of II, a pyridazinone having a 2-methyl rather than the 2'-hydroxyethyl substituent, and a bis(pyridazinonyl)methane analog. In addition, the product of O-alkylation rather than of N-alkylation of 4-acetyl-5,6-bis(4-chlorophenyl)-2H-pyridazin-3-one (I) with ethylene carbonate was detected by high-performance liquid chromatography. The biological activity of these four impurities was compared to that of II.

Animals↗
PubMed1995

New imidazo[1,2-b]pyridazine ligands for peripheral-type benzodiazepine receptors on mitochondria and monocytes.

Several 6-chloro-2,3-disubstituted imidazo[1,2-b]pyridazines, selected from a number of synthetic imidazo[1,2-b]pyridazines which lacked significant binding activity at central benzodiazepine receptors, potently inhibit [3H]diazepam, [3H]Ro5-4864 and [3H]PK11195 binding to rat kidney mitochondrial membranes. In membrane preparations from cultures of THP-1 cells, a human monocytic leukaemia cell line, the isoquinoline carboxamide PK11195 is strongly bound but the benzodiazepine ligands, diazepam and Ro5-4864, are much more weakly bound. The imidazopyridazine compounds which bind strongly to mitochondrial benzodiazepine receptors are very potent displacers of [3H]PK11195 bound to the THP-1 membranes. It appears that the binding properties of these new imidazopyridazine ligands at 'peripheral-type' benzodiazepine receptors resemble those of the isoquinoline carboxamides more than those of the benzodiazepines.

Animals↗
PubMed2004

Mechanism of action of pyridazine analogues on protein tyrosine phosphatase 1B (PTP1B).

The inhibitory effect on PTP1B caused by the addition of pyridazine analogues has been investigated. Biophysical techniques, that is, mass spectrometry (MS), nuclear magnetic resonance (NMR), and isothermal titration calorimetry (ITC) were used for the characterization. Pyridazine analogues cause catalytic oxidation of the reducing agent, generating hydrogen peroxide that oxidizes the active site cysteine on the enzyme, leading to enzyme inactivation. Two additional compound classes show the same effect. We found one common structural feature in these molecules that allows the reaction with triplet molecular oxygen to be less endothermic. A proposed mechanism for the catalytic redox cycle is described.

Catalysis↗
PubMed2004

Imidazo[1,2-b]pyridazines: a potent and selective class of cyclin-dependent kinase inhibitors.

Modification of imidazo[1,2-a]pyridine CDK inhibitors lead to identification of less lipophilic imidazo[1,2-b]pyridazine series of CDK inhibitors. Although several equivalent compounds from these two series have similar structure and show similar CDK activity, the SAR of the two series differs significantly. Protein inhibitor structure determination has confirmed differences in binding mode and given some understanding of these differences in SAR. Potent and selective imidazo[1,2-b]pyridazine inhibitors of CDK2 have been identified, which show >1 microM plasma levels following a 2mg/kg oral dose to mice.

Animals↗
PubMed2006

CoMFA based de novo design of pyridazine analogs as PTP1B inhibitors.

PTP1B plays an important role as a negative regulator in insulin and leptin signaling pathways. Potent and orally active PTP1B inhibitors can act as potential agents for the treatment of Type 2 diabetes and obesity. CoMFA (Comparative Molecular Field Analysis) and de novo ligand design using LeapFrog (LF) studies were performed on pyridazine analogs, reported to be selective and non-competitive inhibitors of PTP1B. A robust model was developed which produced statistically significant results with cross-validated and conventional correlation coefficients of 0.619 and 0.990, respectively. Further, the robustness of the model was verified by bootstrapping analysis. LeapFrog (LF) program is a de novo drug discovery tool, which uses CoMFA maps to generate hypothetical cavity and ligands. As the crystal structure of PTP1B-pyridazine complex is not yet known, the contours of CoMFA model was used to serve as a pharmacophoric model to generate hypothetical cavity for LeapFrog calculations. Ligands were optimized using this concept.

Animals↗
PubMed2006

3-Benzidino-6(4-chlorophenyl) pyridazine blocks delayed rectifier and transient outward potassium current in acutely isolated rat hippocampal pyramidal neurons.

3-[(beta-morpholinoethyl)amino]-4-methyl-6-phenylpyridazine (minaprine) is an acetylcholinesterase (AChE) inhibitor. 3-Benzidino-6(4-chlorophenyl) pyridazine (BCP) and minaprine have a central pyridazine ring in common. In this study, we investigated the effects of BCP on delayed rectifier potassium current (IK(DR)) and transient outward potassium current (IK(A)) in acutely isolated rat hippocampal pyramidal neurons by using whole-cell patch-clamp technique. IK(DR) and IK(A) were inhibited by BCP (0.01-500 microM) in a concentration-dependent and voltage-dependent manner. The IC50 value for the blocking action of BCP on IK(DR) and IK(A) was calculated as 7.13+/-0.18 microM and 0.55+/-0.11 microM, respectively. At the concentration of 10 microM, BCP shifted the activation curve of IK(DR) to positive potential by 29.09 mV. Meanwhile, at the concentration of 10 microM, BCP also shifted the activation and inactivation curve of IK(A) to positive potential by 34.18 and 22.47 mV, respectively. In conclusion, BCP potently inhibits IK(DR) and IK(A) in rat hippocampal pyramidal neurons.

Animals↗
PubMed1993

Synthesis and anti-HIV-1 activity of a series of imidazo[1,5-b]pyridazines.

A series of substituted imidazo[1,5-b]pyridazines have been prepared and tested for inhibitory activity against the reverse transcriptase of HIV-1 (RT) and their ability to inhibit the growth of infected MT-4 cells. Crystal data are reported on two compounds, 15c and 33. From the structure-activity relationships developed within this and other series, it is proposed that key features of the interaction with RT include hydrogen-bond acceptor and aromatic pi-orbital bonding with the imidazopyridazine nucleus and a benzoyl function separated from the heterocycle by a suitable spacer group. Exceptional activity against the reverse transcriptase of HIV-1 (IC50 = 0.65 nM) was obtained with a 2-imidazolyl-substituted derivative, 7-[2-(1H-imidazol-1- yl)-5-methylimidazo-[1,5-b]pyridazin-7-yl]-1-phenyl-1-heptanone (33) which is attributed to additional binding of the imidazole sp2 nitrogen atom. A number of the compounds in this series also inhibit the replication of HIV-1 in vitro in MT-4 and C8166 cells at levels observed with the nucleoside AZT.

Antiviral Agents↗
PubMed2001

Design, synthesis, and structure-activity relationships of a series of 3-[2-(1-benzylpiperidin-4-yl)ethylamino]pyridazine derivatives as acetylcholinesterase inhibitors.

Starting from the 3-[2-(1-benzylpiperidin-4-yl)ethylamino]-6-phenylpyridazine 1, we performed the design, the synthesis, and the structure-activity relationships of a series of pyridazine analogues acting as AChE inhibitors. Structural modifications were achieved on four different parts of compound 1 and led to the following observations: (i) introduction of a lipophilic environment in the C-5 position of the pyridazine ring is favorable for the AChE-inhibitory activity and the AChE/BuChE selectivity; (ii) substitution and various replacements of the C-6 phenyl group are possible and led to equivalent or slightly more active derivatives; (iii) isosteric replacements or modifications of the benzylpiperidine moiety are detrimental to the activity. Among all derivatives prepared, the indenopyridazine derivative 4g was found to be the more potent inhibitor with an IC(50) of 10 nM on electric eel AChE. Compared to compound 1, this represents a 12-fold increase in potency. Moreover, 3-[2-(1-benzylpiperidin-4-yl)ethylamino]-5-methyl-6-phenylpyridazine 4c, which showed an IC(50) of 21 nM, is 100-times more selective for human AChE (human BuChE/AChE ratio of 24) than the reference compound tacrine.

Acetylcholinesterase↗
PubMed1985

Tetracyclic pyridazines as potential psychopharmacological agents.

Since the Z isomer of chlorprothixene (1) is far more active than its E counterpart, it was of interest to develop a stereoselective synthesis for this class of compounds. Insertion of a benzenesulfonamido group at the peri position of a chlorprothixene precursor did affect the stereochemistry of side-chain olefin formation, but after hydrolysis attempted removal of the resulting amine led to a Widman-Stoermer cyclization to afford the corresponding tetracyclic pyridazine-containing compound (4). Since this material displayed encouraging activity in neurotransmitter uptake inhibition studies, compounds in which the sulfur bridge was replaced with an ethano bridge similar to that found in imipramine (8) and with sulfur removed (7) were also prepared. These, together with the corresponding peri amino compounds (3, 5, and 6), were tested as neurotransmitter-uptake The two bridged arylamines 3 and 6 displayed potent and selective inhibition of norepinephrine uptake both when tested in vitro and after in vivo administration. The pyridazine-containing compounds exhibited reasonable activity in vitro, but the activity was lost when they were administered in vivo. None of the compounds displayed significant ability to interfere with spiroperidol binding.

Animals↗
PubMed2003

Imidazo[1,2-b]pyridazines, novel nucleus with potent and broad spectrum activity against human picornaviruses: design, synthesis, and biological evaluation.

A novel structural class of picornavirus inhibitors comprising an imidazo[1,2-b]pyridazine nucleus was discovered. 2-Aminoimidazo[1,2-b]pyridazines (6d, (E/Z)-7b, (E)-7d, (Z)-7d, (E/Z)-8b, (E)-10b, (E)-13a, (Z)-13a, (E)-13b, (Z)-13b, (E)-13c, and (Z)-13c) were designed and synthesized in an effort to identify potent broad spectrum antirhinoviral agents. A practical synthetic route to this chemical scaffold has been developed. The target compounds were evaluated in a plaque reduction assay and in a cytopathic effect assay. Our preliminary SAR studies highlight the minimum structural features required for antirhinovirus activity. Our data suggest that the nature of the linker between the phenyl and the imidazopyridazine moieties has a significant influence on the activity of these compounds. Oximes are slightly better than vinyl carboxamides at this position. The oximes are the most potent analogues against human rhinovirus 14 (HRV-14), and at the concentrations evaluated, no apparent cellular toxicity is noted. Furthermore, the E geometry appears to be a key element for activity; the Z isomer leads to a considerable loss in potency. Of particular interest, analogue 7b exhibits potent broad-spectrum antirhinoviral and antienteroviral activity when evaluated against a panel of seven additional rhino- and enteroviruses. The chemistry and the biological evaluations are discussed.

Antiviral Agents↗
PubMed2004

N-Phenyl-4-pyrazolo[1,5-b]pyridazin-3-ylpyrimidin-2-amines as potent and selective inhibitors of glycogen synthase kinase 3 with good cellular efficacy.

Glycogen synthase kinase 3 regulates glycogen synthase, the rate-determining enzyme for glycogen synthesis. Liver and muscle glycogen synthesis is defective in type 2 diabetics, resulting in elevated plasma glucose levels. Inhibition of GSK-3 could potentially be an effective method to control plasma glucose levels in type 2 diabetics. Structure-activity studies on a N-phenyl-4-pyrazolo[1,5-b]pyridazin-3-ylpyrimidin-2-amine series have led to the identification of potent and selective compounds with good cellular efficacy. Molecular modeling studies have given insights into the mode of binding of these inhibitors. Since the initial leads were also potent inhibitors of CDK-2/CDK-4, an extensive SAR was performed at various positions of the pyrazolo[1,5-b]pyridazin core to afford potent GSK-3 inhibitors that were highly selective over CDK-2. In addition, these inhibitors also exhibited very good cell efficacy and functional response. A representative example was shown to have good oral exposure levels, extending their utility in an in vivo setting. These inhibitors provide a viable lead series in the discovery of new therapies for the treatment of type 2 diabetes.

Amines↗
PubMed2006

Synthesis, structural reassignment, and biological activity of type B MAO inhibitors based on the 5H-indeno[1,2-c]pyridazin-5-one core.

The synthesis and enzyme inhibitor properties of reversible type B monoamine oxidase inhibitors are described. These compounds belong to the 5H-indeno[1,2-c]pyridazine family and possess a hydrophobic benzyloxy or 4,4,4-trifluorobutoxy side chain which, in contrast to a previous assignment, has been unambiguously located at C(8) of the heterocyclic moiety. Investigation of the regioisomeric structures establishes that substitution of the 5H-indeno[1,2-c]pyridazin-5-one core at C(7) vs C(8) dramatically influences the MAO-inhibiting properties of these compounds.

Crystallography, X-Ray↗
PubMed1999

Isoxazolo-[3,4-d]-pyridazin-7-(6H)-one as a potential substrate for new aldose reductase inhibitors.

The isoxazolo-[3,4-d]-pyridazin-7-(6H)-one (2) and its corresponding open derivatives 5-acetyl-4-amino-(4-nitro)-6-substituted-3(2H)pyridazinones (3, 4) were used as simplified substrates for the synthesis of new aldose reductase inhibitors with respect to the previously reported 5, 6-dihydrobenzo[h]cinnolin-3(2H)one-2 acetic acids (1). Moreover, a few derivatives lacking the 5-acetyl group were prepared. Several compounds derived from 2 displayed inhibitory properties comparable to those of Sorbinil. In this class the presence at position 6 of a phenyl carrying an electron-withdrawing substituent proved to be beneficial, independently from its position on the ring (5g,j-l). Acetic acid derivatives were more effective than propionic and butyric analogues. On the contrary, all the monocyclic compounds (6-8) were either inactive or only weakly active. The 3-methyl-4-(p-chlorophenyl)isoxazolo-[3,4-d]-pyridazin-7-(6H )-one acetic acid (5g), which proved to be the most potent derivative, was also investigated in molecular modeling studies, to assess possible similarities in its interaction with the enzyme, with respect to the model 1.

Aldehyde Reductase↗
PubMed2000

Vasorelaxant and antiplatelet activity of 4,7-dimethyl-1,2, 5-oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide: role of soluble guanylate cyclase, nitric oxide and thiols.

1. Certain heterocyclic N-oxides are vasodilators and inhibitors of platelet aggregation. The pharmacological activity of the furoxan derivative condensed with pyridazine di-N-oxide 4,7-dimethyl-1,2, 5-oxadiazolo[3,4-d]pyridazine 1,5,6-trioxide (FPTO) and the corresponding furazan (FPDO) was studied. 2. FPTO reacted with thiols generating nitrite (NO), S-nitrosoglutathione and hydroxylamine (nitroxyl) and converted oxyHb to metHb. FPDO did not generate detectable amounts of NO-like species but reacted with thiols and oxyHb. 3. FPTO and FPDO haem-dependently stimulated the activity of soluble guanylate cyclase (sGC) and this stimulation was inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and by 0.1 mM dithiothreitol. 4. FPTO relaxed noradrenaline-precontracted aortic rings and its concentration-response curve was biphasic (pIC(50)=9. 03+/-0.13 and 5.85+/-0.06). FPDO was significantly less potent vasodilator (pIC(50)=5.19+/-0.14). The vasorelaxant activity of FPTO and FPDO was inhibited by ODQ. oxyHb significantly inhibited only FPTO-dependent relaxation. 5. FPTO and FPDO were equipotent inhibitors of ADP-induced platelet aggregation (IC(50)=0.63+/-0.15 and 0.49+/-0. 05 microM, respectively). The antiplatelet activity of FPTO (but not FPDO) was partially suppressed by oxyHb. The antiaggregatory effects of FPTO and FPDO were only partially blocked by sGC inhibitors. 6. FPTO and FPDO (10 - 20 microM) significantly increased cyclic GMP levels in aortic rings and platelets and this increase was blocked by ODQ. 7. Thus, FPTO can generate NO and, like FPDO, reacts with thiols and haem. The vasorelaxant activity of FPTO and FPDO is sGC-dependent and a predominant role is played by NO at FPTO concentrations below 1 microM. On the contrary, inhibition of platelet aggregation is only partially related to sGC activation.

Animals↗
PubMed1995

Behavioural profile of two potential antidepressant pyridazine derivatives including arylpiperazinyl moieties in their structure, in mice.

The potential antidepressant effects of two pyridazine derivatives, 5-benzyl 6-methyl 2-[4-(3-trifluoro-methyl phenyl) piperazin-1-yl] methylpyridazin-3-one (PC4) and 5-benzyl 6-methyl 2-[4-(3-chlorophenyl) piperazin-1-yl] methylpyridazin-3-one (PC13), were evaluated using classical psychopharmacological tests in mice. The intraperitoneal LD50 values of PC4 and PC13 were respectively 1125.8 and 429.6 mg kg-1. Only at intraperitoneal doses of 100 mg kg-1 did PC4 or PC13 significantly decrease locomotor activity. Both compounds (5-20 mg kg-1, i.p.) reduced the duration of immobility of mice in the forces swimming test, antagonized reserpine (2.5 mg kg-1, i.p.)-induced ptosis, and potentiated reserpine (2.5 mg kg-1, i.p.)-induced hypothermia. PC4 and PC13 (20 mg kg-1, i.p.) partly reversed hypothermia induced by low dose apomorphine (5 mg kg-1, s.c.) but were less effective for higher doses of apomorphine (16 mg kg-1, s.c.). At 200 mg kg-1, intraperitoneal PC13 enhanced the toxic effects of yohimbine (30 mg kg-1, s.c.), while PC4 was inactive. Head twitches produced either by L-5-hydroxytryptophan (4 mg kg-1, i.p.) in mice pretreated with pargyline (100 mg kg-1, i.p.) or by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (3 mg kg-1, i.p.) were antagonized by both pyridazine derivatives (20 mg kg-1, i.p.). PC4 and PC13 showed analgesic properties in the phenylbenzoquinone-induced abdominal constriction test (5.0 < ED50 < 5.5 mg kg-1, i.p.) and in the hot-plate test (10 to 37% of analgesia at 10 mg kg-1, i.p.).(ABSTRACT TRUNCATED AT 250 WORDS)

5-Hydroxytryptophan↗
PubMed1995

Synthetic studies on condensed-azole derivatives. I. Synthesis and anti-asthmatic activities of omega-substituted alkylthioimidazo[1,2-b]pyridazines.

A series of novel omega-substituted alkylthioimidazo[1,2-b]pyridazines was designed and synthesized in an effort to find a novel anti-asthmatic agent. The anti-asthmatic activity of these compounds was evaluated on the basis of their ability to inhibit thromboxane A2 synthetase and platelet activating factor (PAF)-induced bronchoconstriction in guinea pigs. None of these compounds significantly inhibited thromboxane A2 synthetase, though, sulfonamide derivatives potently inhibited PAF-induced bronchoconstriction. Among them, 3-(imidazo[1,2-b]pyridazin-6-yl)thiopropanesulfonamide (5) showed the most potent inhibitory effect. The anti-asthmatic effects of compound 5 in experimental models were superior to those of theophylline.

Animals↗
PubMed1997

Synthetic studies on condensed-azole derivatives. V. Synthesis and anti-asthmatic activities of omega-sulfamoylalkyloxy[1,2,4]triazolo[1,5-b]-pyridazines.

A series of novel ([1,2,4]triazolo[1,5-b]pyridazin-6-yl) oxyalkylsulfonamides was synthesized and evaluated for the ability to inhibit platelet activating factor (PAF)-induced bronchoconstriction in guinea pigs. The compounds bearing a gem-dialkyl or a cycloalkylidene group at the 2 position of the sulfamoylpropyloxy group in the side chain and a methyl group at the 7 position were found to have potent activity. Among them, 2,2-diethyl-3-(7-methyl[1,2,4]- triazolo[1,5-b]pyridazin-6-yl)oxypropanesulfonamide (13) showed excellent anti-asthmatic activity. Compounds 13 may be of significant value in the treatment of asthma and other respiratory diseases. The structure-activity relationships in this series of compounds are discussed.

Animals↗
PubMed1976

A comparative study of the hemodynamic effects of single intravenous doses of 3-hydrazino-6-[N,N-bis-(2-hydroxyethyl)-amino]-pyridazine-dihydrochloride and hydralazine.

The new pyridazine derivative 3-hydrazino-6-[N,N-bis(2-hydroxyethyl)-amino]-pyridazine-dihydrochloride (DL 150 IT) was administered to five hypertensive patients at the dose of 50 mug/kg by i.v. bolus injection. A parallel group of five patiens received 250 mug/kg of hydralazine. Hemodynamic measurements were obtained before treatment, and then after 30--60 and 80-120 min. Cardiac output was evaluated by radiocardiography and myocardial perfusion by clearance of 86Rb. The antihypertensive effect of DL 150 IT was most pronounced 2 h after the injection, whereas by this time the increased heart rate and cardiac output tended to revert to the baseline values. On the contrary, the magnitude of these effects did not change during the observation period after hydralazine treatment. Both drugs increased myocardial perfusion. The new compound appears at least five times more potent than hydralazine and, possibly, has a longer duration of action.

Adult↗