No description available.

Very little is known about why and how the Parkinson's disease (PD) neurodegenerative process begins and progresses. In the course of developments for treatment of PD, the discovery of the inhibition of monoamine oxidase (MAO B) was a conceptual breakthrough, and has now been firmly established. MAO B has also been implicated in the neurodegenerative processes resulting from exposure to xenobiotic amines. For example, MAO B catalyzes the first step of the bioactivation of the parkinsonian inducing pro-neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additional insight into the mechanism of catalysis of MAO B and the mechanism of neurotoxicity by MPTP is therefore very valuable in the pursuit of the treatment of PD. / Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2008.

Very little is known about why and how the Parkinson's disease (PD) neurodegenerative process begins and progresses. In the course of developments for treatment of PD, the discovery of the inhibition of monoamine oxidase (MAO B) was a conceptual breakthrough, and has now been firmly established. MAO B has also been implicated in the neurodegenerative processes resulting from exposure to xenobiotic amines. For example, MAO B catalyzes the first step of the bioactivation of the parkinsonian inducing pro-neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additional insight into the mechanism of catalysis of MAO B and the mechanism of neurotoxicity by MPTP is therefore very valuable in the pursuit of the treatment of PD. / Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2008.

Very little is known about why and how the Parkinson's disease (PD) neurodegenerative process begins and progresses. In the course of developments for treatment of PD, the discovery of the inhibition of monoamine oxidase (MAO B) was a conceptual breakthrough, and has now been firmly established. MAO B has also been implicated in the neurodegenerative processes resulting from exposure to xenobiotic amines. For example, MAO B catalyzes the first step of the bioactivation of the parkinsonian inducing pro-neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Additional insight into the mechanism of catalysis of MAO B and the mechanism of neurotoxicity by MPTP is therefore very valuable in the pursuit of the treatment of PD. / Thesis (Ph.D. (Pharmaceutical Chemistry))--North-West University, Potchefstroom Campus, 2008.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Monoamines appear to play an important modulatory role on pain descending pathways and are involved in the antinociceptive mechanism of several drugs commonly used for the management of pain. In this study, we assessed the involvement of monoamine oxidase B (MAO-B), a key enzyme implicated in monoamine metabolism, on models of postsurgical and neuropathic pain in mice. For this purpose, we evaluated the effects of the selective and irreversible MAO-B inhibitor selegiline on mechanical sensitivity and ex vivo MAO-B activity in different central nervous system regions in mice submitted to incisional and partial sciatic nerve ligation (PSNL) pain models. Mice subjected to plantar incision showed a significant decrease in mechanical threshold when compared with sham-operated mice, characterizing the development of mechanical allodynia. Selegiline, at a dose sufficient to inhibit selectively the MAO-B activity (10 mg/kg), showed an anti-allodynic effect from 0.5 until 6 h after incision. The MAO-B activity was not altered in incision submitted mice when compared with sham-operated animals in any analyzed structure. Likewise, PSNL submitted mice also developed mechanical allodynia, which was reversed by selegiline (10 mg/kg) from 2 until 6 h after treatment. In addition, a significant increase on striatal MAO-B activity was observed in mice subjected to PSNL when compared with sham-operated animals, which was reversed by selegiline treatment. Taken together, our results showed that selegiline presented an antinociceptive effect on mice models of both acute and chronic pain, suggesting a potential involvement of MAO-B on pain mechanisms. / As monoaminas possuem uma função modulatória importante nas vias descendentes do controle da dor e estão envolvidas no mecanismo antinociceptivo de diversos fármacos comumente utilizados no tratamento de síndromes dolorosas. Nesse estudo, nós avaliamos a participação da monoamina oxidase B (MAO-B), uma enzima chave envolvida no metabolismo das monoaminas, em modelos de dor pós-operatória e neuropática em camundongos. Para esse propósito, foram avaliados os efeitos da selegilina, um inibidor seletivo e irreversível da MAO-B, na sensibilidade mecânica e na atividade ex vivo da MAO-B em diferentes regiões do sistema nervoso central (córtex cerebral, estriado e medula espinhal) de camundongos submetidos à incisão plantar ou à ligação parcial do nervo ciático (PSNL). Os camundongos que foram submetidos à incisão plantar apresentaram uma diminuição significativa no limiar mecânico quando comparados aos animais falso-operados, caracterizando o desenvolvimento de alodínia mecânica. Tanto o pré quanto o pós-tratamento com selegilina, em uma dose capaz de inibir seletivamente a atividade da MAO-B (10 mg/kg, p.o.), apresentaram efeito anti-alodínico a partir de 0,5 até 6 h após o tratamento. A atividade da MAO-B, medida 4 h após o procedimento cirúrgico, não foi alterada nos camundongos submetidos à incisão quando comparada com a atividade dos animais falso-operados em nenhuma das estruturas analisadas. Os camundongos submetidos à PSNL também desenvolveram alodínia mecânica, a qual foi revertida pela selegilina (10 mg/kg, p.o.) de 2 até 6 h após o tratamento. Além disso, os camundongos submetidos à PSNL apresentaram um aumento significativo na atividade da MAO-B no estriado 4 h após o tratamento, o qual foi revertido pela selegilina. Foi observado também que a selegilina, em uma dose sem efeito antinociceptivo (1 mg/kg, p.o.) em ambos os modelos de dor utilizados, não foi capaz de inibir a atividade da MAO-B. Nossos resultados mostram que a selegilina apresentou um efeito antinociceptivo tanto em um modelo de dor aguda quanto em um modelo de dor crônica, sugerindo um possível envolvimento da MAO-B nos mecanismos da dor.

No description available.

Molecular modeling is a term referring to the study of proteins, nucleic acids, lipids, and other bio- or macro- or small molecules at the atomistic level using a combination of computational methods, physico-chemical principles, and mathematical functions. It can be generally sub-divided into two areas: molecular mechanics, which is the treatment of atoms and bonds as Newtonian particles and springs, and quantum mechanics, which models electronic behaviors using the Schrödinger equation and wavefunctions. Each technique is a powerful tool that, when used alone or in combination with wet lab experiments, can yield useful results, the products of which have broad applications in studying human disease models, oxidative damage, and other biomolecular processes that are otherwise not easily observed by experiment alone. Within this document, we study seven different such systems. This includes the mode of inhibitor binding to the enzyme monoamine oxidase B, the active site mechanism of that same enzyme, the dynamics of the unstructured p53 C-terminal domain in complex with globular, structured proteins, the process of the viral protein B2 unbinding from double-stranded RNA, and a focus on the dynamics of a variable loop in the antigenic peanut protein Ara h 2. In addition to those conventional molecular modeling studies, several of which were done in tandem with wet lab experiment, we also discuss the validation of charges and charge group parameters for small molecules used in molecular mechanics, and the development of software for the analysis of lipid bilayer systems in molecular mechanics simulations. As computational resources continue to evolve, and as more structural information becomes available, these methods are becoming an integral part of the study of biomolecules in the context of disease. / Ph. D.

<p>This thesis concerns the study of reaction mechanisms by means of kinetic isotope effects (KIEs). Studies of the nucleophilic bimolecular substitution (S_N2) reaction had the dual purpose of improving our fundamental understanding of molecular reactivity and assessing the ability of kinetic isotope effects to serve as mechanistic tools. The transition state of the S_N2 reaction between a cyanide ion and ethyl chloride in tetrahydrofuran was found to be reactant like and only slightly tighter than has been found previously for the same reaction in dimethyl sulphoxide. One conclusion was that the transition-state structure in this reaction was predicted fairly well by the theoretical calculations, even without solvent modelling. The S_N2 reactions between cyanide ions and <i>para</i>-substituted benzyl chlorides were found to have reactant-like transition states, of which the C_α-Cl bond was most influenced by the <i>para</i>-substitution. Theoretical calculations indicated that the chlorine KIEs could be used as probes of the substituent effect on the C_α-Cl bond if bond fission was not too advanced in the transition state. Furthermore, the nucleophile carbon ¹¹C/¹⁴C KIEs were determined for the reactions between cyanide ions and various ethyl substrates in dimethyl sulphoxide.</p><p>Precision conductometry was employed to estimate the aggregation status of tetrabutylammonium cyanide in tetrahydrofuran and in dimethyl sulphoxide, which is of interest as tetrabutylammonium cyanide is frequently used as the nucleophilic reagent in mechanistic investigations and synthetic reactions. The tendency for ion-pair formation was found to be very slight, significant, and very strong in dimethyl sulphoxide, water, and tetrahydrofuran, respectively. </p><p>The nitrogen kinetic isotope effect on monoamine oxidase B catalysed deamination of benzylamine was determined in an attempt to obtain conclusive evidence regarding the mechanism of the oxidation. Monoamine oxidase is an important drug target in connection with the treatment of, for example, depression and Parkinson’s disease, and knowledge on how the enzyme effects catalysis would facilitate the design of highly selective and efficient inhibitors.</p>

This thesis concerns the study of reaction mechanisms by means of kinetic isotope effects (KIEs). Studies of the nucleophilic bimolecular substitution (SN2) reaction had the dual purpose of improving our fundamental understanding of molecular reactivity and assessing the ability of kinetic isotope effects to serve as mechanistic tools. The transition state of the SN2 reaction between a cyanide ion and ethyl chloride in tetrahydrofuran was found to be reactant like and only slightly tighter than has been found previously for the same reaction in dimethyl sulphoxide. One conclusion was that the transition-state structure in this reaction was predicted fairly well by the theoretical calculations, even without solvent modelling. The SN2 reactions between cyanide ions and para-substituted benzyl chlorides were found to have reactant-like transition states, of which the Cα-Cl bond was most influenced by the para-substitution. Theoretical calculations indicated that the chlorine KIEs could be used as probes of the substituent effect on the Cα-Cl bond if bond fission was not too advanced in the transition state. Furthermore, the nucleophile carbon 11C/14C KIEs were determined for the reactions between cyanide ions and various ethyl substrates in dimethyl sulphoxide. Precision conductometry was employed to estimate the aggregation status of tetrabutylammonium cyanide in tetrahydrofuran and in dimethyl sulphoxide, which is of interest as tetrabutylammonium cyanide is frequently used as the nucleophilic reagent in mechanistic investigations and synthetic reactions. The tendency for ion-pair formation was found to be very slight, significant, and very strong in dimethyl sulphoxide, water, and tetrahydrofuran, respectively. The nitrogen kinetic isotope effect on monoamine oxidase B catalysed deamination of benzylamine was determined in an attempt to obtain conclusive evidence regarding the mechanism of the oxidation. Monoamine oxidase is an important drug target in connection with the treatment of, for example, depression and Parkinson’s disease, and knowledge on how the enzyme effects catalysis would facilitate the design of highly selective and efficient inhibitors.

Parkinson’s disease (PD) is a neurodegenerative disorder that is characterised by a reduction of dopamine concentration in the striatum due to degeneration of dopaminergic neurons in the substantia nigra. Currently, first line treatment of PD includes the use of dopamine precursors, dopamine agonists and inhibitors of enzymatic degradation of dopamine, in an effort to restore dopamine levels and/or its effects. However, all these therapeutic strategies are only symptomatic and unfortunately do not slow, stop or reverse the progression of PD. From the discovery of adenosine A2A receptor-dopamine D2 receptor heteromers and the antagonistic interaction between these receptors, the basis of a new therapeutic approach towards the treatment of PD emerged. Adenosine A2A receptor antagonists have been shown to decrease the motor symptoms associated with PD, and are also potentially neuroprotective. The possibility thus exists that the administration of an adenosine A2A antagonist may prevent further neurodegeneration. Furthermore, the antagonism of adenosine A1 receptors has the potential of treating cognitive deficits such as those associated with Alzheimer's disease and PD. Therefore, dual antagonism of adenosine A1 and A2A receptors would be of great benefit since this would potentially treat both the motor as well as the cognitive impairment associated with PD. The affinities (Ki-values between 0.6 mM and 38 mM) of a series of 1,4-dihydropyridine derivatives were previously illustrated for the adenosine A1, A2A and A3 receptor subtypes by Van Rhee and co-workers (1996). These results prompted this pilot study, which aimed to investigate the potential of the structurally related 3,4-dihydropyrimidin-2(1H)-ones (dihydropyrimidones) and 2-amino-1,4-dihydropyrimidines as adenosine A1 and A2A antagonists. In this pilot study, a series of 3,4-dihydropyrimidones and 2-amino-1,4-dihydropyrimidines were synthesised and evaluated as adenosine A1 and A2A antagonists. Since several adenosine A2A antagonists also exhibit MAO inhibitory activity, the MAO-inhibitory activity of selected derivatives was also assessed. A modified Biginelli one pot synthesis was used for the preparation of both series of compounds under solvent free conditions. A mixture of a β- diketone, aldehyde and urea/guanidine hydrochloride was heated for an appropriate time to afford the desired compounds in good yields. MAO-B inhibition studies comprised of a fluorometric assay where kynuramine was used as substrate. A radioligand binding protocol described in literature was employed to investigate the binding of the compounds to the adenosine A2A and A1 receptors. The displacement of N-[3H]ethyladenosin-5’-uronamide ([3H]NECA) from rat striatal membranes and 1,3-[3H]-dipropyl-8-cyclopentylxanthine ([3H]DPCPX) from rat whole brain membranes, was used in the determination of A2A and A1 affinity, respectively. The results showed that both 3,4-dihydropyrimidones and 2-amino-1,4-dihydropyrimidines had weak adenosine A2A affinity, with the p-fluorophenyl substituted dihydropyrimidone derivative (1h) in series 1, exhibiting the highest affinity for the adenosine A2A receptor (28.7 μM), followed by the p-chlorophenyl dihydropyrimidine derivative (2c) in series 2 (38.59 μM). Both series showed more promising adenosine A1 receptor affinity in the low micromolar range. The p-bromophenyl substituted derivatives in both series showed the best affinity for the adenosine A1 receptor with Ki-values of 7.39 μM (1b) and 7.9 μM (2b). The pmethoxyphenyl dihydropyrimidone (1d) and p-methylpneyl dihydropyrimidine (2e) derivatives also exhibited reasonable affinity for the adenosine A1 receptor with Ki-values of 8.53 μM and 9.67 μM, respectively. Neither the 3,4-dihydropyrimidones nor the 2-amino-1,4- dihydropyrimidines showed MAO-B inhibitory activity. Comparison of the adenosine A2A affinity of the most potent derivative (1h, Ki = 28.7 μM) from this study with that of the previously synthesised dihydropyridine derivatives (Van Rhee et al., 1996, most potent compound had a Ki = 2.74 mM) reveals that an approximate 100- fold increase in binding affinity for A2A receptors occurred. However, KW6002, a known A2A antagonist, that has already reached clinical trials, has a Ki-value of 7.49 nM. The same trend was observed for adenosine A1 affinity, where the most potent compound (1b) of this study exhibited a Ki-value of 7.39 μM compared to 2.75 mM determined for the most potent dihydropyridine derivatives (Van Rhee et al., 1996). N6-cyclopentyladenosine (CPA), a known adenosine A1 agonist that was used as a reference compound, however had a Kivalue of 10.4 nM. The increase in both adenosine A1 and A2A affinity can most likely be ascribed to the increase in nitrogens in the heterocyclic ring (from a dihydropyridine to a dihydropyrimidine) since similar results were obtained by Gillespie and co-workers in 2009 for a series of pyridine and pyrimidine derivatives. In their case it was found that increasing the number of nitrogens in the heterocyclic ring (from one to two nitrogen atoms for the pyridine and pyrimidine derivatives respectively) increased affinity for the adenosine A2A and adenosine A1 receptor subtypes, while three nitrogen atoms in the ring (triazine derivatives) were associated with decreased affinity. It thus appears that two nitrogen atoms in the ring (pyrimidine) are required for optimum adenosine A1 and A2A receptor affinity. The poor adenosine A2A affinity exhibited by the compounds of this study can probably be attributed to the absence of an aromatic heterocyclic ring. The amino acid, Phe-168 plays a very important role in the binding site of the A2A receptor, where it forms aromatic - - stacking interactions with the heterocyclic aromatic ring systems of known agonists and antagonists. Since the dihydropyrimidine ring in both series of this pilot study was not aromatic, the formation of aromatic - -stacking interactions with Phe-168 is unlikely. In conclusion, the 3,4-dihydropyrimidone and 2-amino-1,4-dihydropyrimidine scaffolds can be used as a lead for the design of novel adenosine A1 and A2A antagonists, although further structural modifications are required before a clinically viable candidate will be available as potential treatment of PD. / MSc (Pharmaceutical Chemistry), North-West University, Potchefstroom Campus, 2014