Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 98-111).

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L'élongation de peptides ou d'acides aminés N-acylés via une activation C-terminale (par exemple par un carbodiimide) est délaissée en synthèse peptidique à cause de l'épimérisation rapide des intermédiaires 5(4H)- oxazolones issus de cette activation. Au contraire, cela représente une voie prometteuse en chimie prébiotique où les substrats sont a priori racémiques, et où une étape d'épimérisation peut favoriser un scénario protométabolique / autocatalytique d'émergence de l'homochiralité. Partant de travaux récents qui montraient clairement que l'activation C-terminale de peptides en milieu aqueux procède surtout via une 5(4H)-oxazolone, nous avons étudié la stéréosélectivité des couplages peptidiques qui en résultent dans des conditions prébiotiques plausibles (milieu aqueux dilué à pH faiblement acide). Notre étude sur des peptides modèles (préparés par des méthodes classiques de synthèse peptidique et comportant un résidu tyrosine qui facilite l'analyse par HPLC) visait à évaluer l'effet de la configuration des résidus voisins ou des nucléophiles ; elle a montré la formation d'excès diastéréomériques significatifs en faveur de dérivés homochiraux, sous l'influence prépondérante de la chiralité du nucléophile.Nous avons ensuite étudié la réactivité de dipeptides libres dans les mêmes conditions, pour évaluer la formation compétitive de dicétopipérazine (DCP), qui est susceptible de bloquer l'élongation au-delà du dipeptide. La formation de DCP est prépondérante à partir de dipeptides faiblement activés, mais n'a pas lieu en présence d'agents d'activation de potentiel élevé (e.g. l'EDC) qui favorisent la formation plus rapide d'oxazolone et permet l'élongation peptidique ; ces derniers résultats soulignent l'importance prébiotique de potentiels d'activation élevés. / The elongation of peptides or N-acylamino acids through C-terminus activation is usually avoided in peptide synthesis, because of the fast epimerisation of 5(4H)-oxazolones intermediates resulting form such activation. Conversely, it represents a promising perspective in prebiotic chemistry where substrates are assumed to be racemic, and where an epimerisation step may favour a protometabolic / autocatalytic scenario of emergence of homochirality.Based on recent works which clearly showed that the C-terminus activation of peptides in aqueous media mostly proceed through a 5(4H)-oxazolone, we investigated the stereoselectivity of peptide couplings resulting therefrom under plausible prebiotic conditions (dilute aqueous medium at weakly acidic pH). Our study on model peptides (prepared by classical peptide synthesis methods, and bearing a tyrosine residue which facilitates HPLC analysis), aimed at assessing the influence of the configuration of the vicinal peptide residue or of the nucleophile; we observed significant diastereomeric excesses in favour of homochiral sequences, under the preponderant influence of the chirality of the nucleophile.Then we investigated the reactivity of free dipeptides under the same conditions, to assess the extent of diketopiperazine (DKP) formation, which may prevent further elongation beyond dipeptides. While DCP formation is preponderant from weakly activated peptides, id does not occur in the presence of high potential activation agents (e.g. EDC), which favour the faster formation of oxazolone and allow subsequent peptide eleongation; these last results undeline the prebiotic importance of high activation potentials.

Le travail décrit dans ce manuscrit présente l'utilisation de deux techniques immunoenzymatiques pour le criblage à haut débit de catalyseurs chimiques et biologiques. Ces méthodes, jusqu'à présent réservées au monde du diagnostic sont employées ici pour la découverte de nouveaux catalyseurs pour des réactions énantiosélectives ainsi que pour des réactions de couplage. Les dosages immunologiques « par compétition » faisant appel aux anticorps monoclonaux se sont avérés des excellents outils pour le criblage à haut débit de catalyseurs asymétriques pour les réactions d'insertion de carbénoïdes dans la liaison OH de l'eau tandis que celles utilisant des anticorps polyclonaux ont été utilisées avec succès pour le criblage de biocaytalyseurs pour la réaction d'ouverture énantiosélective des oxazolones par l'eau. Un autre type de méthode utilisant des anticorps monoclonaux, appelée « sandwich » nous a permis de réaliser le criblage à haut débit de catalyseurs pour la réaction de cycloaddition alcyne-azoture.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / A Fisalina E (FIS E), isolada das partes aÃreas da Physalis angulata (Solanaceae), foi avaliada em modelos de dermatite de contato induzida por 12-O-tetradecanoilforbol-13-acetato (TPA) e por oxazolona (OXA) em camundongos. A dermatite de contato irritativa aguda foi induzida pela administraÃÃo tÃpica de TPA (2,5μg/orelha) e avaliada apÃs 4h. A FIS E(0,125;0,25 e 0,5 mg/orelha,por via tÃpica) reduziu de forma significativa o edema de orelha induzido por TPA em 33,1; 38,7; 39%, respectivamente, e dexametasona(0,05 mg/orelha,por via tÃpica) reduziu em 95,2%. Nas mesmas doses, a FIS E assim como a Dexa, reduziram em 45,7; 52,5; 67,6 e 83,4 %, respectivamente, a atividade da mieloperoxidase (MPO) tecidual. FIS E (3, 10 e 30 mg/kg,por via oral) e Dexa (1mg/kg,por via oral) reduziram o edema de orelha em 34,8; 40,7, 47,3 e 46,6% respectivamente. Nas mesmas doses, a FIS E assim como a Dexa, reduziram em 39,3; 46,7 e 54,3 e 81,7 %, respectivamente, a atividade da mieloperoxidase (MPO) tecidual. A FIS E (0.5 mg/orelha) foi capaz de reduzir os nÃveis teciduais de TNF-α de 8,711.18 pg/ml (veÃculo) para 2,950.81 pg/ml e a dexametasona (0,05 mg/orelha) para 2,350.94 pg/ml, representando uma reduÃÃo de 66,2 e de 73 %, respectivamente. A administraÃÃo de Mifepristone (25 mg/kg,s.c), antagonista esteroidal, reverteu os efeitos da FIS E e da Dexa, por via oral e tÃpica, sobre a reduÃÃo do edema, atividade da mieloperoxidase e nÃveis de TNF-α. Na marcaÃÃo imunohistoquÃmica para TNF-α e NF-κB, a FIS E (0,5 mg/orelha) e a dexametasona (0,05 mg/orelha) reduziram a intensidade de marcaÃÃo do TNF-α e NF-κB, e o Mifepristone, reverteu esse efeito. A aÃÃo antiinflamatÃria da FIS E no modelo da dermatite aguda induzida por TPA foi confirmada pelos achados histopatolÃgicos, com a reduÃÃo do edema, infiltrado inflamatÃrio de mono e polimorfonucleares. Na dermatite crÃnica foi induzida pela aplicaÃÃo tÃpica de 20 Âl de uma soluÃÃo de TPA (2,5Âg/orelha) em dias alternados durante 10 dias, a FIS E, por via tÃpica, nas doses 0,125; 0,25 e 0,5 mg/orelha, reduziu, de forma significativa, o edema de orelha, em 19, 23 e 30,3%, respectivamente, enquanto a Dexa (0,05mg/orelha) reduziu em 32,6 %. FIS E (0,125;0,25 e 0,5 mg/orelha,por via tÃpica) e a Dexa(0,05mg/orelha) reduziram a atividade tecidual da MPO em 30; 38,8; 50,8 e 56,6%, respectivamente. A administraÃÃo oral da FIS E (3, 10 e 30 mg/kg), reduziu, de forma significativa, o edema de orelha crÃnico, em 8; 14,8; 17 %, respectivamente, e a Dexa (1 mg/kg) reduziu em 20,7 %.Nas mesmas doses, a FIS E e a Dexa reduziram a atividade da MPO em 43,1; 54,5 ;59,3 e 65 %,respectivamente. O modelo de dermatite de contato induzida por oxazolona (OXA, 1%/orelha), provocou uma hiperplasia epidÃrmica onde o INF-γ teve papel crucial. A FIS E, por via oral e tÃpica, reduziu de forma significativa, a hiperplasia epidÃrmica do 7Â ao 19Â dia de observaÃÃo. A FIS E (0.5 mg/orelha, por via tÃpica) diminuiu os nÃveis de IFN-γ em 43,5% e a Dexa (0.05 mg/orelha, via tÃpica) em 37,5%.Os resultados encontrados, comprovados pelo estudo histolÃgico, demonstram o efeito antiinflamatÃrio da Fisalina no modelo de dermatite de contato alÃrgica crÃnica. ConcluÃmos que a Fisalina E demonstrou atividade antiinflamatÃria, por via tÃpica e oral, nos modelos de dermatite de contato induzida por TPA e oxazolona em camundongos, possivelmente atravÃs da interaÃÃo com receptores de glicocorticÃides. / The physalin E (PHY E), isolated from the aerial parts of Physalis angulata (Solanaceae), was assessed in models of contact dermatitis induced by 13-acetate-12-o-tetradecanoyl-phorbol (TPA) and oxazolone (OXA) in mice. The irritant contact dermatitis was induced by acute topical administration of TPA (2,5 mg/ear) and evaluated after 4h. The PHY E topically applied to ear at 0,125;0,25 and 0,5 mg/ear and dexamethasone (Dexa), topically, a dose of 0,05 mg/ear, reduced significantly the edema ear induced by TPA in 33,1; 38,7; 39 and 95,2%, respectively. In the same doses, PHY E as well as Dexa, reduced by 45,7; 52,5; 67,6 and 83,4%, respectively, the activity of myeloperoxidase (MPO) in tissue. Oral administration of PHY E (3,10 and 30 mg/kg) and DEXA (1 mg/kg) decreased the ear edema by 34,8; 40,7;47,3 and 46,6% respectively. The same doses, PHY E as well as Dexa, reduced by 39,3; 46,7;54,3% and 81,7%, respectively, the activity of myeloperoxidase (MPO) tissue. The PHY E (0,5 mg/ear) was able to reduce the tissue levels of TNF-α of 8,711.18 pg/ml (vehicle) to 2,950.81 pg/ml and dexamethasone (0,05 mg/ear) to 2,350.94 pg/ml, showing a reduction of 66.2 and 73%, respectively.The administration of mifepristone (25 mg/kg,sc),a steroid antagonist, reversed the effects of PHY E and Dexa, orally and topically, on reducing the edema,myeloperoxidase activity and levels of TNF-α. In the immunohistochemical analysis for TNF-α and NF-κB, PHY E (0,5 mg/ear) and dexamethasone (0,05 mg/ear) reduced the intensity of marking the TNF-α and NF-κB, and mifepristone reversed this effect. The anti-inflammatory action of the PHY E in the model of the dermatitis TPA-induced were confirmed by histopathological findings, with the reduction of edema and inflammatory infiltration of mono and polymorphonuclear. The chronic dermatitis was induced by application of 20 Âl solution of TPA (2,5 mg/ear) was applied topically every other day for 10 days, PHY E topically applied (0,125, 0,25 and 0,5 mg/ear) reduced significantly the edema of the ear, 19; 23; 30,3%,and Dexa (0,05 mg/ear) decreased by 32,6%.In the same doses, PHY E and Dexa reduced tissue activity of MPO in 30; 38,8;50,8 and 56,6%, respectively. Oral administration. PHY E (3, 10 and 30 mg/kg) reduced significantly the ear edema chronic in 8, 14,8 and 17%, respectively, and Dexa (1 mg/kg) reduced in 20.7%. In the same doses,PHY E and Dexa reduced activity of MPO in 43.1, 54.5, 59.3 and 65% respectively The model of contact dermatitis induced by oxazolone (OXA, 1%/ear) caused an epidermal hyperplasia where the INF-γ played crucial role. PHY E oral and topical, has significantly reduced the epidermal hyperplasia of 7 th to 19 th day of observation Physalin E (0,5 mg/ear topically) decreased levels of IFN-γ in 43,5% and Dexa (0,05 mg/ear topically) to 37,5% when compared to vehicle. Our results, as evidenced by histological study, demonstrate the anti-inflammatory effect of physalin in the model of contact dermatitis allergic. In conclusion, the results obtained showed that PHY E presented anti-inflammatory activity either when was used by oral and topical route in the models of contact dermatitis TPA and Oxazolone-induced in mice, possible trought the interaction with glucocorticoids receptors.