Central Nervous System Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Central Nervous System Agents) - Volume 17, Issue 1, 2017

Alzheimer's disease (AD) is the most common neurodegenerative disorder and demands approaches for prevention and delayed onset. The development of therapeutics for AD is based on the amyloid cascade hypothesis (vaccines, β- and γ-Secretase inhibitors), or targeting tau and neurofibrillary tangle formation, neuroinflammation, etc. Cholinesterase, BACE-1, amyloid-β 1-42, γ and β-Secretase, and Phosphodiesterase type IV (PDE4) inhibitors are the reported treatment options. Among these, the γ- and β-Secretase inhibitors can be clustered in several heterocyclic classes (imidazoles, thiazoles, indoles, benzaldehydes, pyrimidine, etc), with subsequent description of the structure-activity relationships, and extended to the pharmacological profile in order to evaluate their drug-likeness, with special attention to toxicity and bioavailability. This article discusses the approaches proposed by several research groups working on the synthesis of enzyme inhibitors, based on modelling studies and the way these findings were used to obtain new drugs for the treatment of AD.

Thiazolidines are multifaceted molecules and exhibit various kinds of biological activities including anticonvulsant and antidepressant activities, chemically thiazolidinediones is a diversified class of heterocyclic nucleus. Thiazolidinediones have shown significant biological activities in various CNS disorder. The mechanism responsible for thiazolidinediones biological activities in CNS based on thiazolidinediones- induced neuroprotection, which is useful in the prevention of microglial activation as well as cytokine expression. The cytokine expression is responsible for inflammatory condition. At the molecular level thiazolidinediones are responsible for the prevention of activation of pro-inflammatory transcription factor as well as promoting the anti-oxidant mechanism in the CNS. In the present article author has elaborated importance of structure activity relationship, molecular mechanism and biological activities with respect to central nervous system. Various investigations suggest that thiazolidinediones may pave the way for the design as well as the discovery of new drug candidates.

Anticonvulsant refers to a group of pharmaceuticals used in the treatment of epileptic seizures. The use of current antiepileptic drugs has been questioned due to the non selectivity of the drugs and the undesirable side effects produced by them. This led to the search for antiepileptic compounds with more selectivity and lower toxicity. Semicarbazones have been developed as versatile anticonvulsant pharmacophore. It has displayed potent anticonvulsant effect in a wide variety of preclinical anticonvulsant models. Till date various semicarbazone derivatives containing 1,3,4-oxadiazole, 1,3,4- thiadiazole, pyrimidine, benzothiazole and substituted phenyl/aryl ring have been synthesized and evaluated for anticonvulsant activity. The semicarbazone based pharmacophore model with four binding sites is essential for anticonvulsant activity. This model comprises of an aryl hydrophobic binding site, hydrogen bonding domain, an electron donor group and another hydrophobic-hydrophilic site regulating the pharmacokinetic properties of the anticonvulsant. Extensive structure-activity relationship has demonstrated that compound with OH, CH3O, NO2, Cl, F, Br substituents in the arylhydrophobic pocket, nitro, hydroxy group on distant phenyl ring and a hydrogen bonding domain possess anticonvulsant activity. In this review, advances made in the application of semicarbazones as a versatile pharmacophore model for the design of new anticonvulsant drugs are being updated and suggested for future drug design and development of novel anticonvulsants.

Background: Hydrazone core is a versatile structural linker for the development of various classes of antiepileptic agents. The aim of this study was to investigate the anticonvulsant activity of thiophene based hydrazones according to the antiepileptic drug development program protocol. Methods: The maximal electroshock-induced seizure and 6 Hz "Psychomotor" seizure test models in mice were performed. Additionally, the active compounds in the screening test were subsequently subjected to the maximal electroshock-induced seizure test that allowed determination of their median effective doses and median toxic doses. The most active compound was also subjected to the In vitro Hippocampal slice culture neuroprotection assay. Results: Among the synthesized compounds, 1-(thiophen-2-yl) ethylidene] hydrazine carboxamides (THb) and 1-(thiophen-2-yl) ethylidene] hydrazine carbothioamide (THc) showed a broad-spectrum anticonvulsant activity since they were active in both maximal electroshock-induced seizure and 6Hz- Psychomotor induced seizure models with no neurotoxicity. In the mice maximal electroshock-induced seizure screen, compound THb gave an ED50 of 11.8 mg/kg and a TD50 of 39.47 mg/kg, resulting in a good protection index (PI), that is, TD50/ED50, of 3.3 when compared to Phenobarbital and Valproate. THb (100μM) was also found to be effectively suppressing network hyperexcitability in the in vitro mECHC spontaneous bursting model, as determined by effects on spontaneous burst activity and duration. Conclusion: The suggested pharmacophore model for lead compounds from thiophene based hydrazones is explained by the hydrophobic domain-thiophene, electron donor-imine and hydrogen bonding domain-carboxamide or carbothioamide unit.

Background: Degradation of the inhibitory neurotransmitter γ-aminobutyric acid (GABA) is mainly catalysed by GABA aminotransferase (GABA-AT), excessive activity of which leads to convulsions. Inhibition of GABA-AT increases the concentration of GABA and can terminate the convulsions. Several studies have revealed that GABA analogues could be the outstanding scaffolds for the design of potent inhibitors of GABA-AT. The poor ability of GABA analogues to cross the blood–brain barrier (BBB), always produces low therapeutic index.` However, Vigabatrin, a mechanism-based inhibitor of GABA-AT, is currently approved treatment of epilepsy, but it has harmful side effects, leaving a need for improved GABA-AT inactivators. Experimental design: In our present in silico investigation, AutoDock 4.2,-based on Lamarckian genetic algorithm was employed for virtual screen of a compound library with 35 entries (Schiff’s bases of GABA) in search for novel and selective inhibitors of GABA-AT. Results: By means of flexible type of molecular docking, we proposed that these designed molecules could successfully bind into the active pocket of GABA-AT with good predicted affinities in comparison to standard vigabatrin. Among the designed analogues, HIG18, HIG28 and HIG30 showed significant binding free energy of -10.25, -9.88 and -9.31 kcal/mol with predicted inhibitory constant values of 0.03, 0.05 and 0.15 μM respectively. Conclusion: Using ligand-based drug design, we proposed that electron withdrawing phenyl substituted heterocyclic imines of GABA could be considered as promising structures for synthesis and testing of new GABA-AT inhibitors from this class. We hypothesize that novel GABA analogues with an azomethine linkage incorporated with heterocyclic system can have increased affinity and more lipophilic character that would provide a probability of having less toxic effect in the therapy of convulsions.

Background: Epilepsy is a neurological disorder, characterized by seizures accompanied by loss or disturbance of consciousness affecting various physical and mental functions. Current anticonvulsant drugs are effective in controlling seizures in about 70% of cases, but their use is often limited by side effects like ataxia, megaloblastic anemia, hepatic failure. In search for a novel anticovulsant drug with better efficacy and lower toxicity, a series of novel pyrimidine based semicarbazone were designed and evaluated for antiepileptic activity. Methods: The test compounds were designed on the basis of four site binding hypothesis proposed for anticonvulsant activity. The chemical structures of the test compounds were elucidated using spectral (IR, 1H NMR, 13C NMR and MS) and elemental analysis. The minimal motor impairment activity was determined in mice using rotorod test. The maximal electroshock seizure (MES) and subcutaneous pentylenetrtrazole (scPTZ) models were employed for anticonvulsant evaluation. Results: The results reveal that 76% of the compounds were active in the MES screening as compared to 53% of the compounds in the scPTZ test. Test compounds showed some MES selectivity displaying their effectiveness in generalized seizures of the tonic-clonic type. The molecular docking analysis of semicarbazone derivatives showed good ligand-receptor interactions with specially hydrogen bond interactions with ARG192, GLU270 and THR353 amino acid of receptor. Conclusion: The present report confirms that pharmacophore model with four binding sites is crucial for anticonvulsant activity in the semicarbazones.

Background: The nervous system is responsible for the communication between the organism and its environment. This task is possible by the presence of the myelin sheath, which is a double membrane formed by about 75% lipids and 25% proteins. The sulfatide represents one of the main lipids of the myelin band; its degradation is catabolized by the enzyme Arylsulfatase A (ARSA), to generated galactosylceramide. Mutations affecting ARSA function lead to the neurodegenerative disease Metachromatic Leukodystrophy. This disease is characterized by accumulation of sulfatide within the band of myelin affecting its functionality. The biochemical consequences of ARSA deficiency are not well understood yet. Objective and Method: In this paper, we used an in-silico systems-biology approach to model the biochemical consequences of ARSA deficiency within a general human metabolic network (Recon2) and a glia cellular model. Results: We expected that ARSA deficiency mainly affected the glycosphingolipid pathways. However, the results suggest that mitochondrial metabolism and amino acid transport were the main reactions affected within both cellular models. In the glia cell model, it was highlighted the high number of affected reactions of neurotransmitters metabolism, while only a reduced effect was observed in reactions involved in glycosphingolipids metabolism. Conclusion: We hypothesize that ARSA deficiency might lead to metabolic consequences that not only compromise the myelin band or the glycosphingolipids metabolism but also the overall metabolic function of the nervous system. Furthermore, these results offer the bases for the design of in-vitro and in-vivo experiments that allow generating new knowledge of MLD pathophysiology and other neurodegenerative diseases.

Background: Diabetes mellitus is a chronic degenerative disease responsible for hyperglycemic episodes through insulin secretion deficiency or cellular resistance. Clinical diagnosis in diabetic patients established that this disease affects the CNS, damaging the brain and impairing cognition, thus establishing a clinical diabetic condition named diabetic encephalopathy. Despite the fact that physiological mechanisms responsible for the development of diabetic encephalopathy are still unclear, an excessive formation of reactive oxygen species, an alteration of acetylcholinesterase activity and a reduction of growth factor levels may be related with the pathogenesis of this condition. Pharmacological treatments with natural compounds have been proven to be useful in the treatment of a wide variety of diseases through their antioxidant actions. Methods: This study built a compendium of chemical compounds used for the treatment of diabetic encephalopathy demonstrating the most important physiological targets that future drugs should aim for. Results: As previously suspected, antioxidants and acetylcholinesterase inhibitors were useful to prevent memory loss in streptozotocin-induced animals. In addition, growth factors showed an improvement of memory in diabetic rodents. Most of the studies focused on antioxidant compounds despite cross studies researching both antioxidants and acetylcholinesterase activities. Conclusion: Therefore, it could be suggested that future studies regarding treatments for diabetic encephalopathy should focus on the antioxidant profile and acetylcholinesterase, since they seem to play pivotal roles in cognitive impairment in diabetes. No less important, studies with growth factors are also important physiological targets for treatment of diabetic encephalopathy.