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

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.

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.

Synthesis and complete assignment of the 1H and 13C NMR spectra of 6-substituted and 2,6-disubstituted pyridazin-3(2H)-ones

Several pyridazin-3(2H)-one derivatives were synthesized starting from alkyl furans using oxidation with singlet oxygen to give 4-methoxy or 4-hydroxybutenolides, key intermediates of the synthetic strategy followed. For all pyridazinones reported, a complete assignment of the (1)H and (13)C NMR spectra using one- and two-dimensional NMR spectroscopic methods, which included NOE, DEPT, COSY, HSQC and HMBC experiments, was accomplished. Correlations between the chemical shifts of the heterocyclic ring atoms and substituents at N-2 and C-6 were analyzed.

1H, 13C, and 15N NMR spectra of some pyridazine derivatives

(1)H, (13)C, and (15)N NMR chemical shifts for pyridazines 4-22 were measured using 1D and 2D NMR spectroscopic methods including (1)H-(1)H gDQCOSY, (1)H-(13)C gHMQC, (1)H-(13)C gHMBC, and (1)H-(15)N CIGAR-HMBC experiments.

4-Amino-5-substituted-3(2H)-pyridazinones as Orally Active Antinociceptive Agents: Synthesis and Studies on the Mechanism of Action

A number of 4-amino-5-vinylpyridazinones and 4-amino-5-heterocyclic-pyridazinones were synthesized and tested for their analgesic activity. Many of these compounds, tested at doses of 3-20 mg kg-1 po, showed good antinociceptive activity, reducing by more than 50% the number of writhes with respect to controls. Compounds 16c, 19a, 20a, and 28 were the most potent of the series because they were able to induce a potent antinociceptive effect at a dose of 3 mg kg-1 po. None of the active compounds at the analgesic dose provoked any visible change in normal behavior, as demonstrated in the rotarod test. Studies on the mechanism of action showed that the analgesia induced by the active compounds was completely prevented by pretreatment with the alpha2-antagonist yohimbine, suggesting an involvement of alpha2-adrenoceptors. Further investigation demonstrated an indirect activation of the noradrenergic system through an amplification of noradrenaline release.

Arylpiperazinylalkylpyridazinones and Analogues as Potent and Orally Active Antinociceptive Agents: Synthesis and Studies on Mechanism of Action

A number of arylpiperazinylalkylpyridazinones structurally related to the previously described lead A (5-{[4-(3-chlorophenyl)piperazin-1-yl]-propyl}-3-methyl-7-phenylisossazolo[4,5-d]pyridazin-4-(5H)-one) were synthesized and tested for their analgesic activity. Many of the tested molecules, at the dose of 20 mg kg-1 p.o., showed high antinociceptive activity, in particular, compounds 5a, 11c, 15a, 21 and 22, which were able to reduce the number of abdominal constrictions by more than 50% in writhing test. The pharmacological investigation of lead A led us to clarify the mechanism of action of this compound, showing that it carries out its analgesic action through the inhibition of reuptake of noradrenaline. The antinociception of some of the most interesting new molecules was completely prevented by pretreatment with alpha2-antagonist yohimbine, suggesting the involvement of alpha2-adrenoceptors, as with prototype A.