Novel heterocyclic-fused pyridazinones as potent and selective phosphodiesterase IV inhibitors

Isoxazolo[3,4-d]pyridazinones positively modulate the metabotropic glutamate subtypes 2 and 4

Isoxazolo[3,4-d] pyridazinones ([3,4-d]s) are selective positive modulators of the metabotropic glutamate receptors (mGluRs) subtypes 2 and 4, with no functional cross reactivity at mGluR1a, mGLuR5 or mGluR8. Modest binding for two of the [3,4-d]s is observed at the allosteric fenobam mGluR5 site, but not sufficient to translate into a functional effect. The structure activity relationship (SAR) for mGluR2 and mGluR4 are distinct: the compounds which select for mGluR2 all contain fluorine on the N-6 aryl group. Furthermore, the [3,4-d]s in this study showed no significant binding at inhibitory GABAA, nor excitatory NMDA receptors, and previously we had disclosed that they lack significant activity at the System Xc-Antiporter. A homology model based on Conn's mGluR1 crystal structure was examined, and suggested explanations for a preference for allosteric over orthosteric binding, subtype selectivity, and suggested avenues for optimization of efficacy as a reasonable working hypothesis.

Diazo Strategy for the Synthesis of Pyridazines: Pivotal Impact of the Configuration of the Diazo Precursor on the Process

Phosphazenes of vinyldiazocarbonyl compounds having cis stereochemistry of the functional groups on the vinyl bond readily produce pyridazines by a diaza-Wittig process, whereas their counterparts with trans configuration remain intact under similar reaction conditions. Upon UV irradiation trans-phosphazenes furnish pyridazines through a tandem trans-to-cis isomerization followed by intramolecular cyclization. At elevated temperatures trans-(triphenyl)phosphazenes dissociate to give the initial vinyldiazo compounds, which produce pyrazoles in high yields. The first theoretical study on the mechanism of the diaza-Wittig process by DFT calculations at the M06-2X/6-31G(d) level of theory suggest that for the cis-phosphazenes a rapid tandem [2+2] cycloaddition/cycloelimination process with low energy barriers is preferred over trans isomers.

Coordination compounds of a hydrazone derivative with Co(iii), Ni(ii), Cu(ii) and Zn(ii): synthesis, characterization, reactivity assessment and biological evaluation

Increasing inhibitory effect of Zn-Hp2DAP < Hp2DAP < Co-Hp2DAP on ABC transporter MDR1 drug efflux pump.

Antinociceptive, anti-inflammatory and smooth muscle relaxant activities of the pyrrolo[3,4-d]pyridazinone derivatives: Possible mechanisms of action

The aim of this study was to evaluate the analgesic as well as anti-inflammatory activities of the new pyrrolo[3,4-d]pyridazinone derivatives. Moreover, the present study attempted to assess some of the mechanisms involved in the pharmacological activity of these compounds. In the previous studies it was shown that these compounds were highly active in the phenylbenzoquinone-induced 'writhing syndrome' test and had much lower activity in the hot plate, which indicates that mainly peripheral mechanisms of analgesia are involved in their effects. In these extended studies the analgesic activity of two tested compounds (4c, 4f) was confirmed in some animal models of pain. The studied compounds showed a significant and dose-related antinociceptive effect in the models of pain induced by formalin, capsaicin and glutamic acid. Both compounds decreased the edema formation and one of them (4c) attenuated mechanical hyperalgesia in carrageenan-induced paw inflammation in rats. Furthermore, both compounds inhibited cell migration, plasma exudation and nociceptive reaction in zymosan A-induced mouse peritonitis. In the subsequent studies, including experiments on isolated organs (ileum, trachea, aorta), radioligand assays and biochemical tests, it was demonstrated that analgesic and anti-inflammatory effects of the investigated structures are largely due to their competitive antagonism for histamine H1 receptor. The influence on the level of cAMP in inflammatory cells (shown in RAW 264.7 macrophages) and subsequent inhibition of cytokine (TNFα, IL-1β) release can also be one of the important mechanisms of their action. Moreover some additional mechanisms may also be involved in the eventual analgesic effect of tested pyrrolo[3,4-d]pyridazinone derivatives.

Microwave accelerated synthesis of isoxazole hydrazide inhibitors of the system xc- transporter: Initial homology model

Microwave accelerated reaction system (MARS) technology provided a good method to obtain selective and open isoxazole ligands that bind to and inhibit the Sxc- antiporter. The MARS provided numerous advantages, including: shorter time, better yield and higher purity of the product. Of the newly synthesized series of isoxazoles the salicyl hydrazide 6 exhibited the highest level of inhibitory activity in the transport assay. A homology model has been developed to summarize the SAR results to date, and provide a working hypothesis for future studies.

Impairment of locomotor activity induced by the novel N-acylhydrazone derivatives LASSBio-785 and LASSBio-786 in mice

The N-acylhydrazone (NAH) analogues N-methyl 2-thienylidene 3,4-benzoylhydrazine (LASSBio-785) and N-benzyl 2-thienylidene 3,4-benzoylhydrazine (LASSBio-786) were prepared from 2-thienylidene 3,4-methylenedioxybenzoylhydrazine (LASSBio-294). The ability of LASSBio-785 and LASSBio-786 to decrease central nervous system activity was investigated in male Swiss mice. LASSBio-785 or LASSBio-786 (30 mg/kg, ip) reduced locomotor activity from 209 ± 26 (control) to 140 ± 18 (P < 0.05) or 146 ± 15 crossings/min (P < 0.05), respectively. LASSBio-785 (15 or 30 mg/kg, iv) also reduced locomotor activity from 200 ± 15 to 116 ± 29 (P < 0.05) or 60 ± 16 crossings/min (P < 0.01), respectively. Likewise, LASSBio-786 (15 or 30 mg/kg, iv) reduced locomotor activity from 200 ± 15 to 127 ± 10 (P < 0.01) or 96 ± 14 crossings/min (P < 0.01), respectively. Pretreatment with flumazenil (20 mg/kg, ip) prevented the locomotor impairment induced by NAH analogues (15 mg/kg, iv), providing evidence that the benzodiazepine (BDZ) receptor is involved. This finding was supported by the structural similarity of NAH analogues to midazolam. However, LASSBio-785 showed weak binding to the BDZ receptor. LASSBio-785 or LASSBio-786 (30 mg/kg, ip, n = 10) increased pentobarbital-induced sleeping time from 42 ± 5 (DMSO) to 66 ± 6 (P < 0.05) or 75 ± 4 min (P < 0.05), respectively. The dose required to achieve 50% hypnosis (HD₅₀) following iv injection of LASSBio-785 or LASSBio-786 was 15.8 or 9.5 mg/kg, respectively. These data suggest that both NAH analogues might be useful for the development of new neuroactive drugs for the treatment of insomnia or for use in conjunction with general anesthesia.

Functionalized pyrazoles and pyrazolo[3,4-d]pyridazinones: Synthesis and evaluation of their phosphodiesterase 4 inhibitory activity

A series of pyrazoles and pyrazolo[3,4-d]pyridazinones were synthesized and evaluated for their PDE4 inhibitory activity. All the pyrazoles were found devoid of activity, whereas some of the novel pyrazolo[3,4-d]pyridazinones showed good activity as PDE4 inhibitors. The most potent compounds in this series showed an IC(50) in the nanomolar range. The ability to inhibit TNF-alpha release in human PBMCs was determined for two representative compounds, finding values in the sub-micromolar range. SARs studies demonstrated that the best arranged groups around the heterocyclic core are 2-chloro-, 2-methyl- and 3-nitrophenyl at position 2, an ethyl ester at position 4 and a small alkyl group at position 6. Molecular modeling studies performed on a representative compound allowed to define its binding mode to the PDE4B isoform.

Pharmacological characterization of (3-thienylidene)-3,4-methylenedioxybenzoylhydrazide: a novel muscarinic agonist with antihypertensive profile

BACKGROUND

Several new bioactive compounds of the N-acylhydrazone class were developed from the safrole, a Brazilian natural product obtained from sassafras oil (Ocotea pretiosa). This work investigated the effects on cardiovascular system of LASSBio-897, a new analogue of the lead compound 3,4-methylenedioxybenzoyl-2-thienylhydrazone named LASSBio-294.

METHODS

Thoracic aorta from Wistar-Kyoto (WKY) rats was prepared for isometric tension recording and for cGMP content determination. Blood pressure (BP) was measured in WKY rats and spontaneously hypertensive rats (SHR) after treatment with 1 mg/kg intravenously of LASSBio-897 and during 14 days' treatment of SHR with 1 mg/kg/day perorally.

RESULTS

LASSBio-897 (0.05-1 micromol/l) exhibited a potent vasodilatory activity in phenylephrine (Phe)-contracted aortic rings from WKY rats. This effect was abolished in endothelium-denuded aortic rings and after treatment with the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) or the guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Also, LASSBio 897 (1 micromol/l) increased about 15 times the intracellular content of cGMP. LASSBio-897-induced vasodilation was totally inhibited by the muscarinic antagonist atropine and by the M(3) subtype selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), indicating the involvement of M(3) receptors. Intravenous administration of LASSBio-897 (1 mg/kg) produced significant hypotensive response in both WKY and SHR. The hypotensive effect of LASSBio-897 was also observed during the 14 days of oral administration.

CONCLUSIONS

The novel N-acylhydrazone derivative LASSBio-897 exhibited a potent vasodilatory activity in aortic rings mediated by the NO/cGMP pathway via activation of endothelial M(3) receptors and was orally effective in reducing BP on SHR.

Isoxazole analogues bind the system xc- transporter: structure-activity relationship and pharmacophore model

Analogues of amino methylisoxazole propionic acid (AMPA), were prepared from a common intermediate 12, including lipophilic analogues using lateral metalation and electrophilic quenching, and were evaluated at System xc-. Both the 5-naphthylethyl-(16) and 5-naphthylmethoxymethyl-(17) analogues adopt an E-conformation in the solid state, yet while the former has robust binding at System xc-, the latter is virtually devoid of activity. The most potent analogues were amino acid naphthyl-ACPA 7g, and hydrazone carboxylic acid, 11e Y=Y'=3,5-(CF(3))(2), which both inhibited glutamate uptake by the System xc- transporter with comparable potency to the endogenous substrate cystine, whereas in contrast the closed isoxazolo[3,4-d] pyridazinones 13 have significantly lower activity. A preliminary pharmacophore model has been constructed to provide insight into the analogue structure-activity relationships.

A Regioselective One-Pot, Three Component Synthesis of 6-Aryl-4-cyano-3(2H)-pyridazinones in Water

A series of 4-cyano-3(2H)-pyridazinones bearing different aryl substituents in the 6-position of the pyridazinone ring was synthesized regioselectively using a novel efficient one-pot three component reaction of alkyl 2-cyanoacetates with arylglyoxals in the presence of hydrazine hydrate at room temperature in water.

Design, synthesis, and evaluation of 2-aryl-7-(3',4'-dialkoxyphenyl)-pyrazolo[1,5-a]pyrimidines as novel PDE-4 inhibitors

Described herein is design, synthesis, and biological evaluation of novel series of 2-aryl-7-(3',4'-dialkoxyphenyl)-pyrazolo[1,5-a]pyrimidines acting as inhibitors of type 4 phosphodiesterase (PDE4) which is known as a good target for the treatment of asthma and COPD. For this purpose, structure optimization was conducted with the aid of structure-based drug design using the known X-ray crystallography. Also, biological effects of these compounds on the target enzyme were evaluated by using in vitro assays, leading to the potent and selective PDE-4 inhibitor (IC(50)<10nM).

Synthesis of some new imidazo[3″,4″:1′,2′] pyrimido[4′,5′:4,5]thieno[2,3-c] pyridazines and other fused thieno[2,3-c]pyridazines

5-Amino-3,4-diphenylthieno[2,3-c]pyridazine-6-carboxamide was prepared and used as starting material to form the novel 6-chloromethyl-3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8(7H)-one (3), the 6-(arylaminomethyl) compounds (4a–c), 7-aryl-7,8-dihydro-3,4-diphenylimidazo[3″,4″:1′,2′]pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-10(6H)-ones (5a–c), ethyl 7,8-dihydro-8-oxopyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine-6-acetate (6) and its carbohydrazide (7). The pyridazinothienopyrimidotriazepinedione 8, pyridothienopyridazine 12 and pyridazinothienooxazepine 13 were also prepared.

Novel pyrazolopyrimidopyridazinones with potent and selective phosphodiesterase 5 (PDE5) inhibitory activity as potential agents for treatment of erectile dysfunction

Pyrazolo[1',5':1,6]pyrimido[4,5-d]pyridazin-4(3H)-ones and their analogues, potentially useful for the treatment of erectile dysfunction, were synthesized and evaluated as inhibitors of phosphodiesterase 5 (PDE5). Several compounds showed IC50 values in the low nanomolar range, and in particular, compound 5r, displaying high potency toward PDE5 (IC50 = 8.3 nM) and high selectivity versus PDE6 (240-fold) appeared to be a very promising new lead both in comparison with the potent but not selective sildenafil and in comparison with some analogues previously reported by us. SAR studies in this triheterocyclic scaffold led us to conclude that the best arranged groups are a methyl in position 1, a benzyl in position 3, a phenyl in position 9, and a linear four-carbon chain in position 6.

Local anti-inflammatory effect and behavioral studies on new PDE4 inhibitors

Phosphodiesterase 4 (PDE4) inhibitors are effective anti-inflammatory drugs, although some adverse effects are observed in animals and humans. These effects have forced researchers to find new PDE4 inhibitors with less adverse effects. We recently reported the synthesis of novel heterocyclic-fused pyridazinones that inhibit PDE4. As a first step in the study of the anti-inflammatory properties of these compounds, we studied the effects of local administration of these pyridazinone derivatives in a mouse model of acute inflammation. We found that 6-Benzyl-3-methyl-4-phenylpyrazolo[3,4-d]pyridazin-7(6H)-one (CC4), ethyl 6,7-dihydro-6-ethyl-3-methyl-7-oxo-4-phenyl-thieno[2,3-d]pyridazine-2-carboxylate (CC6) and ethyl 6,7-dihydro-6-ethyl-3-methyl-4-phenyl-1H-pyrrolo[2,3-d]pyridazine-2-carboxylate (CC12) reduced the paw edema induced by zymosan in mice as rolipram (the PDE4 inhibitor prototype with anti-inflammatory activity) and indomethacin did. It is well known that rolipram locally administered induces some adverse effects such as hyperalgesia. Thus, we studied this effect after local administration of CC4, CC6 and CC12 in the formalin test. We found that CC6 induced hyperalgesic effects, whereas CC4 and CC12 did not change the nociceptive threshold. Furthermore, we found that rolipram and CC6 reduced locomotor activity, whereas CC4 and CC12 did not change locomotor performance of the mice. Since CC4 and CC12 neither affected the nociceptive threshold nor changed the locomotor performance of mice, they appear more suitable than CC6 for future studies on animals and could be developed as an anti-inflammatory drug for humans.

Synthesis and vasodilatory activity of new N-acylhydrazone derivatives, designed as LASSBio-294 analogues

Conventional therapy to treat hypertension often involves arterial vasodilation. Decrease of blood pressure by vasodilators is normally associated with adverse effects because of their low vascular selectivity. This is of interest to develop new molecules with potential for clinical use and fewer side effects. Recently, a new bioactive compound of the N-acylhydrazone class, LASSBio-294, was shown to produce a cardioinotropic effect and vasodilation. In this report, new derivatives of LASSBio-294 were designed and tested on the contractile response of vascular smooth muscle from Wistar rats. Phenylephrine-induced contracture in the aorta was inhibited by the derivatives LASSBio-785 and LASSBio-788. The concentrations necessary to cause 50% reduction of the maximal vascular response (IC50) were 10.2 +/- 0.5 and 67.9 +/- 6.5 microM. Vasodilation induced by both derivatives is likely to be mediated by a direct effect on smooth muscle because it was not dependent on the integrity of vascular endothelium. LASSBio-785 was seven times more potent than the reference compound LASSBio-294 (IC50 = 74 microM) in producing an endothelium-independent vasodilator effect.

New pyrazolo[1′,5′:1,6]pyrimido[4,5-d]pyridazin-4(3H)-ones as potent and selective PDE5 inhibitors

A series of potent PDE5 inhibitors with high selectivity versus PDE6 isoenzymes was identified.

Synthesis and complete 1H, 13C and 15N NMR assignment of substituted isoxazolo[3,4-d]pyridazin-7(6H)-ones

The synthesis and complete assignment of all hydrogen, carbon and nitrogen NMR signals of several new isoxazolo[3,4-d]pyridazin-7(6H)-ones is reported. The spectroscopic characterization is extended to previously described analogues.

Isoxazolo[3,4-d]pyridazinones and analogues as Leishmania mexicana PDE inhibitors

A series of isoxazolopyridazinones and analogues has been prepared and evaluated as Leishmania mexicana phosphodiesterase (PDE) inhibitors. Some of the synthesized compounds showed a moderate PDE inhibitory activity at 100 microM and preliminary structure-activity relationships were discussed.

Synthesis, structure-activity relationships, and pharmacological profile of 9-amino-4-oxo-1-phenyl-3,4,6,7-tetrahydro[1,4]diazepino[6, 7,1-hi]indoles: discovery of potent, selective phosphodiesterase type 4 inhibitors

The synthesis, structure-activity relationships, and biological properties of a novel series of potent and selective phosphodiesterase type 4 (PDE4) inhibitors are described. These new aminodiazepinoindoles displayed in vitro PDE4 activity with submicromolar IC(50) values and PDE4 selectivity vs PDE1, -3, and -5. Specifically, one compound (CI-1044, 10e) provided efficient in vitro inhibition of TNFalpha release from hPBMC and hWB with IC(50) values of 0.34 and 0.84 microM, respectively. This compound was found to exhibit potent in vivo activity in antigen-induced eosinophil recruitment in Brown-Norway rats (ED(50) = 3.2 mg/kg po) and in production of TNFalpha in Wistar rats (ED(50) = 2.8 mg/kg po). No emetic side effects at therapeutic doses were observed in ferrets.

Conformational difference between PDE4 apoenzyme and holoenzyme

The type 4 cAMP-specific phosphodiesterases (PDE4s) are Mg(2+)-dependent hydrolases that catalyze the hydrolysis of 3', 5'-cAMP to AMP. Previous studies indicate that PDE4 exists in two conformations that bind the inhibitor rolipram with affinities differing by more than 100-fold. Here we report that these two conformations are the consequence of PDE4 binding to its metal cofactor such as Mg(2+). Using a fluorescence resonance energy transfer (FRET)-based equilibrium binding assay, we identified that L-791,760, a fluorescent inhibitor, binds to the apoenzyme (free enzyme) and the holoenzyme (enzyme bound to Mg(2+)) with comparable affinities (K(d) approximately 30 nM). By measuring the displacement of the bound L-791,760, we have also identified that other inhibitors bind differentially with the apoenzyme and the holoenzyme depending upon their structure. CDP-840, SB-207499, and RP-73401 bind preferentially to the holoenzyme. The conformational-sensitive inhibitor (R)-rolipram binds to the holoenzyme and apoenzyme with affinities (K(d)) of 5 and 300 nM, respectively. In contrast to its high affinity (K(d) approximately 2 microM) and active holoenzyme complex, cAMP binds to the apoenzyme nonproductively with a reduced affinity (K(d) approximately 170 microM). These results demonstrate that cofactor binding to PDE4 is responsible for eliciting its high-affinity interaction with cAMP and the activation of catalysis.

Phosphodiesterase 4 inhibitors, structurally unrelated to rolipram, as promising agents for the treatment of asthma and other pathologies

An increase of cyclic adenosine and guanosine monophosphate (cAMP and cGMP) level can be achieved by inhibition of phosphodiesterases (PDEs), which are the enzymes responsible for the conversion of these second messengers into the corresponding 5-monophosphate inactive counterparts. The high heterogeneity in PDE families and in their tissue distribution, as well as their different functional role, make these enzymes very attractive targets for medicinal chemists. The PDE 4 family is particularly abundant in immunocompetent cells, where an increase of cAMP leads to the inhibition of the synthesis and release of pro-inflammatory mediators, cytokines and active oxygen species. Moreover PDE 4 inhibitors are able to reduce bronchial smooth muscle tone in vitro and show bronchodilatory effects in vivo. Thus, the current therapy for asthma, which is based on a combination of beta(2) agonists and corticosteroids, could be replaced by treatment with PDE 4 inhibitors. This review mainly covers PDE 4 inhibitors structurally related to xanthines and Nitraquazone, which appear to be very attractive models for the synthesis of novel PDE 4 inhibitors potentially useful for the treatment of asthma, chronic pulmonary obstructive disease and some autoimmune diseases. These compounds could be devoid of the central side-effects (nausea, vomiting, headache) of the archetypal Rolipram, which hampered its development as a drug. The review also highlights the novel structural classes of PDE 4 inhibitors recently reported in the literature.

Novel adrenoceptor antagonists with a tricyclic pyrrolodipyridazine skeleton

A still unknown tricyclic heterocyclic system (5) was synthesized from 6-hydroxy-2-methylpyridazin-3-one and its structure identified as 2,8-dichloro-6-methylpyrrolo[1,2-b:3,4-d']dipyridazin-5(6H)- one by spectroscopic investigations. Selective condensation of 5 with 2-[4-(2-substituted-phenyl)piperazin-1-yl]ethylamine gave the 2-arylpiperazinylethylamino-8-chloro derivatives 6a-c, which were investigated in binding studies toward the three alpha1-adrenergic and 5-HT1A-serotonergic receptor subtypes. They displayed high potency on all the assays and some selectivity for alpha1a and alpha1d subtypes.