Synthesis, neuronal activity and mechanisms of action of halogenated enaminones

Synthesis, Theoretical Study, and Anticonvulsant Evaluation of N-Arylenaminones

N-Arylenaminones are highly versatile compounds which can be synthesized in relatively simple ways. In this work we explored the synthesis of the four monosubstituted N-(4-R-phenyl)enaminones 3 a (R=NO2), 3 b (R=F), 3 c (R=H), and 3 d (R=OMe) with the goal of determining the influence of the substituents' electronic effects on tautomer stability and biological activity. These compounds were analyzed by means of Density Functional Theory calculations (DFT), to evaluate the relative stability of the possible tautomers. We found that the enaminone structure is the most stable with respect to the ketoimine and iminoenol forms. In addition, all four compounds display anticonvulsant activity, with 3 d being the one that mostly increased latency and mostly decreased the number of convulsions with respect to the control group. The suggested mechanism of action involves blockage of the voltage-dependent Na+ channels, considering that these molecules meet the structural characteristics needed to block the receptor, as is the case of the positive control molecules phenytoin (PHT) and valproic acid (VPA).

Copper-Catalyzed Thiolation of Terminal Alkynes Employing Thiocyanate as the Sulfur Source Leading to Enaminone-Based Alkynyl Sulfides under Ambient Conditions

A highly efficient protocol for copper-catalyzed thio-alkynylation of enaminone-based thiocyanates with terminal alkynes under mild conditions has been developed. This scalable amino group-directed thio-alkynylation proceeds in the open air with a broad substrate scope and an excellent yield. The demonstrated synthetic transformation creates the opportunity for a wide variety of sulfur-containing useful materials. Gram-scale synthesis and further synthetic transformations of alkynyl sulfides highlight the potential utility of the method.

Autocatalyzed three-component cyclization of polyfluoroalkyl-3-oxo esters, methyl ketones and alkyl amines: a novel approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones

A new one-pot reaction between polyfluoroalkylated 3-oxo esters, methyl ketones and primary or secondary alkyl amines is reported as an efficient approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones. The scope of three-component cyclization and its plausible mechanism are discussed. The described protocol makes it possible to vary the functional substituents in 2, 3 and 5 positions of carbocycles. Anhydrous conditions are necessary for the productive synthesis of aminocyclohexenones, whereas in the presence of water the competitive formation of alkyl ammonium salts of keto hydroxy carboxylates is observed. Dehydration of the aminocyclohexenones was effectively used for the synthesis of 3-alkylamino-5-trifluoromethylphenols, some of which exhibited moderate antifungal activities against eight pathogenic fungal strains.

Design, synthesis and biological evaluation of piperazino-enaminones as novel suppressants of pro-Inflammatory cytokines

Infection triggers the release of pro-inflammatory cytokines (TNF-alpha and IL-6). Over-production, however, cause tissue injury seen in severe asthma. The ability of enaminone E121 to reduce pro-inflammatory cytokines in our laboratory encouraged further examination of its structural scaffold. Piperazino-enaminones were designed by incorporating n-arylpiperazine motif into the aromatic enaminone. Four possible modifications were explored systematically. Synthesis was accomplished by amination of the corresponding methyl/ethyl 2,4-dioxo-6-(substituted)cyclohexane-carboxylate.. Sixteen novel compounds were synthesized. Biological activity was tested in J774 macrophages stimulated with lipopolysaccharides. The release of cytokines was measured via ELISA. Four compounds significantly suppressed TNF-alpha and IL-6 release in dose-dependent manner.

Anti-Inflammatory Properties of the Enaminone E121 in the Dextran Sulfate Sodium (DSS) Colitis Model

BACKGROUND

Enaminones are synthetic compounds with an established role in the prevention of various forms of seizures. Recent evidence suggests potent anti-tussive, bronchodilation and anti-inflammatory properties. Pre-treatment with particularly E121 compound resulted in a decrease in leukocyte recruitment in the ovalbumin induced-model of asthma, immune cell proliferation and cytokine release in vitro. We hypothesize that E121 might serve as a therapeutic potential in intestinal inflammation through modulating immune cell functions.

METHODS

Colitis was induced by daily dextran sulfate sodium (DSS) administration for 5 days, and its severity was determined by gross and histological assessments. The plasma level of various cytokines was measured using flow cytometry-based assay. The colonic expression/ phosphorylation level of various molecules was determined by immunofluorescence and western blotting. The effects of E121 treatment on in vitro neutrophil chemotaxis (under-agarose assay), superoxide release (luminol oxidation assay) and apoptosis (annexin V/7AAD) were also determined.

RESULTS

DSS-induced colitis in mice was significantly reduced by daily E121 treatment (30-100 mg/kg) at gross and histological levels. This effect was due to modulated plasma levels of interleukin (IL-2) and colonic expression levels of various signaling molecules and proteins involved in apoptosis. In vitro neutrophil survival, chemotaxis, and superoxide release were also reduced by E121 treatment.

CONCLUSION

Our results indicate important anti-inflammatory actions of E121 in the pathogenesis of IBD.

Evaluation of the antinociceptive activities of enaminone compounds on the formalin and hot plate tests in mice

Recently, we found that methyl 4-(4′-bromophenyl)aminocyclohex-3-en-6-methyl-2-oxo-1-oate (E139), an anticonvulsant enaminone, has antinociceptive activity in the hot plate test. In this study we evaluated the antinociceptive activity of five anilino enaminones E139, ethyl 4-(4′-chlorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E121), ethyl 4-(4′-bromophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E122), methyl 4-(4′-chlorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (E138) and ethyl 4-(4′-fluorophenyl)amino-6-methyl-2-oxocyclohex-3-en-1-oate (BRG 19) using the formalin and hot plate tests. E139 has been reported to exert its effects via enhancement of extracellular GABA levels, thus tiagabine, a GABA transporter inhibitor, was evaluated as a control together with indomethacin. Tiagabine had antinociceptive activity in both phase 1 (neurogenic pain) and phase 2 (inflammatory pain) of the formalin test, whereas indomethacin had activity only in phase 2. E139 and E138 had antinociceptive activity in both phases of the formalin test, whereas E121 had activity only in phase 1 and BRG 19 had activity only in phase 2. E122 had no significant activity in either phase. In the hot plate test only E139 had antinociceptive activity. Administration of either bicuculline, a GABA_A receptor antagonist, or CGP 35348, a GABA_B receptor antagonist, blocked the antinociceptive activity of E139. In conclusion our results indicate that E139 has antinociceptive activity in the formalin and hot plate tests that are dependent on GABA receptors.

Synthesis of enaminones and their difluoroboron complexes through domino aryl migration

A new domino strategy for selective synthesis of enaminones and their difluoroboron complexes through aryl migration has been developed. The reaction features low-cost and readily accessible starting materials, reliable scalability, and bond-forming efficiency as well as simple one-pot operation, which makes this strategy highly viable for future applications.

Allosteric Modulation of GABAA Receptors by an Anilino Enaminone in an Olfactory Center of the Mouse Brain

In an ongoing effort to identify novel drugs that can be used as neurotherapeutic compounds, we have focused on anilino enaminones as potential anticonvulsant agents. Enaminones are organic compounds containing a conjugated system of an amine, an alkene and a ketone. Here, we review the effects of a small library of anilino enaminones on neuronal activity. Our experimental approach employs an olfactory bulb brain slice preparation using whole-cell patch-clamp recording from mitral cells in the main olfactory bulb. The main olfactory bulb is a key integrative center in the olfactory pathway. Mitral cells are the principal output neurons of the main olfactory bulb, receiving olfactory receptor neuron input at their dendrites within glomeruli, and projecting glutamatergic axons through the lateral olfactory tract to the olfactory cortex. The compounds tested are known to be effective in attenuating pentylenetetrazol (PTZ) induced convulsions in rodent models. One compound in particular, KRS-5Me-4-OCF₃, evokes potent inhibition of mitral cell activity. Experiments aimed at understanding the cellular mechanism underlying the inhibitory effect revealed that KRS-5Me-4-OCF₃ shifts the concentration-response curve for GABA to the left. KRS-5Me-4-OCF₃ enhances GABA affinity and acts as a positive allosteric modulator of GABA_A receptors. Application of a benzodiazepine site antagonist blocks the effect of KRS-5Me-4-OCF₃ indicating that KRS-5Me-4-OCF₃ binds at the classical benzodiazepine site to exert its pharmacological action. This anilino enaminone KRS-5Me-4-OCF₃ emerges as a candidate for clinical use as an anticonvulsant agent in the battle against epileptic seizures.

Evaluation of anticonvulsant actions of dibromophenyl enaminones using in vitro and in vivo seizure models

Epilepsy and other seizure disorders are not adequately managed with currently available drugs. We recently synthesized a series of dibromophenyl enaminones and demonstrated that AK6 and E249 were equipotent to previous analogs but more efficacious in suppressing neuronal excitation. Here we examined the actions of these lead compounds on in vitro and in vivo seizure models. In vitro seizures were induced in the hippocampal slice chemically (zero Mg2+ buffer and picrotoxin) and electrically using patterned high frequency stimulation (HFS) of afferents. In vivo seizures were induced in rats using the 6 Hz and the maximal electroshock models. AK6 (10 µM) and E249 (10 µM) depressed the amplitude of population spikes recorded in area CA1 of the hippocampus by -50.5±4.3% and -40.1±3.1% respectively, with partial recovery after washout. In the zero Mg2+ model, AK6 (10 µM) depressed multiple population spiking (mPS) by -59.3±6.9% and spontaneous bursts (SBs) by -65.9±7.2% and in the picrotoxin-model by -43.3±7.2% and -50.0±8.3%, respectively. Likewise, E249 (10 µM) depressed the zero-Mg2+-induced mPS by -48.8±9.5% and SBs by -55.8±15.5%, and in the picrotoxin model by -37.1±5.5% and -56.5±11.4%, respectively. They both suppressed post-HFS induced afterdischarges and SBs. AK6 and E249 dose-dependently protected rats in maximal electroshock and 6 Hz models of in vivo seizures after 30 min pretreatment. Their level of protection in both models was similar to that obtained with phenytoin Finally, while AK6 had no effect on locomotion in rats, phenytoin significantly decreased locomotion. AK6 and E249, suppressed in vitro and in vivo seizures to a similar extent. Their in vivo activities are comparable with but not superior to phenytoin. The most efficacious, AK6 produced no locomotor suppression while phenytoin did. Thus, AK6 and E249 may be excellent candidates for further investigation as potential agents for the treatment of epilepsy syndromes with possibly less CNS side effects.