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Stereoselective Synthesis of <i>β</i>-Mannosides and <i>β</i>-Mannosamines <i>via</i> Cs<sub>2</sub>CO<sub>3</sub>-Mediated Anomeric <i>O</i>-Alkylation.Bhetuwal, Bishwa Raj January 2020 (has links)
No description available.
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Synthesis of Indolo[3,2-b]carbazoles via an Anomeric-Based Oxidation Process: A Combined Experimental and Computational StrategyZolfigol, M.A., Khazaei, A., Karimitabar, F., Hamidi, M., Maleki, F., Aghabarari, B., Sefat, Farshid, Mozafari, M. 01 February 2018 (has links)
No / Indolo[3,2-b]carbazole is a molecule of great biological significance, as it is formed in vivo after
consumption of cruciferous vegetables. The reaction of 1H-indole and various aldehydes in the presence
of a catalytic amount of N,2-dibromo-6-chloro-3,4-dihydro-2H-benzo[e][1,2,4]thiadiazine-7-sulfonamide
1,1-dioxide as an efficient and homogeneous catalyst in acetonitrile at 50°C produces 6,12-disubstituted
5,7-dihydroindolo[2,3-b]carbazole with an in good to excellent yield. The presented technique offers a fast
and robust method, by the use of inexpensive commercially available starting materials toward 6,12-
disubstituted 5,7-dihydroindolo[2,3-b]carbazole. A new anomeric-based oxidation was kept in mind for
the final step of the indolo[2,3-b]carbazoles synthesis. The suggested anomeric-based oxidation mechanism
was supported by experimental and theoretical evidences. / The Grant of Allameh Tabataba’i’s Award, Grant Number: BN093
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Modulation and Recognition of Nucleic Acid StructuresSpring, Alexander M 21 June 2012 (has links)
The fidelity of an organism’s genome is central to biology. DNA, however, is constantly being damaged and modified by a variety of sources. As a result of these changes, repair enzymes, polymerases, and other interrogating biomolecules must be able to recognize, repair, and adapt to a multitude of different structures and dynamics presented. Manipulation of natural systems via the development and introduction of novel bases and DNA structures only adds to this complexity. In addition, specific RNA sequences are becoming more prevalent therapeutic and diagnostic targets. These include retroviruses and other viruses that maintain their genome with RNA. Unlike DNA, RNA poses a unique challenge as targets due to their highly diverse secondary and tertiary structures. In this manuscript, three different nucleic acid systems were chosen to investigate how intramolecular and intermolecular interactions impact their own structure as well as giving further insight into how nucleic acids are recognized and distorted by interrogating damage specific enzymes as well as structure specific proteins.
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The oxidation of glucose in aqueous solution by oxygenOlson, Richard E. 01 January 1967 (has links)
No description available.
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C2 alkoxyl anion participation in the base-catalyzed reaction of p-nitrophenyl beta-D-galctoside and p-nitrophenyl alpha-D-mannosideGasman, Robert C. 01 January 1966 (has links)
No description available.
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Méthodologies de synthèses pour la préparation de ‘puces à SAS’ : vers de nouveaux outils pour l’étude des interactions héparane sulfate /protéines / Synthetic methodologies for the preparations of SAS chips : generation of new tools to decipher Heparan Sulfate-Protein interactionsLiu, Wenqing 23 January 2015 (has links)
L’Héparane sulfate (HS) est un polysaccharide linéaire et sulfaté présent à la surface des cellules ou dans le milieu extracellulaire des tissus animaux. Le long des chaines d'HS, des régions présentant une densité de charge négative élevée (domaines S) alternent avec des régions plus faiblement chargées (domaines A). Différents motifs SAS sont ainsi exposés à la surface des cellules et permettent des interactions spécifiques avec de nombreuses protéines comme l’interféron gamma (INF-γ). Cette cytokine interagit avec haute affinité avec les chaines d'HS, ce qui module son activité in vivo (accumulation et localisation tissulaire, clairance sanguine). Pour moduler l’activité de l’INF-γ en inhibant ses interactions avec les chaines d'HS de la surface des cellules, nous avons entrepris la synthèse de mimes de motifs SAS, dans lesquels des fragments synthétiques de domaines S sont liés par un espaceur de longueur modulable. Pour effectuer cette conjugation, nous avons choisi d'utiliser deux types de chimie click la "CuAAC" et la "ligation oxime". Cette stratégie a nécessité de mettre au point des fonctionnalisations orthogonales des extrémités réductrices et non réductrices d'oligosaccharides synthétiques. Nous avons mis au point les réactions sur un disaccharide modèle dérivé du cellobiose, puis les avons transférées à la modification d'un tetrasaccharide synthétique d'HS. Dans ce travail, nous avons optimisé deux réactions clef : une alkylation anomérique dans l’eau et une allylation de fonction alcool dans des conditions neutres / Heparan sulfate (HS) is a linear polysaccharide found in animal tissues at the cell surface or in the extracellular matrix. HS chains display alternating highly negatively charged regions (S) and less charged ones (A). SAS domains with different topologies can thus be exposed at the cell surface with the aim of interacting specifically with different proteins. Gamma interferon (INF-γ) is a cytokine that binds tightly to HS chains. This interaction allows controlling numerous bioactivities of the cytokine (accumulation and location in tissues as well as blood clearance). The discovery of HS fragment able to modulate the activity of IFN-γ could open the way to new innovative therapeutics. To this aim we launched a program aiming at synthesizing mimetic of the SAS motifs found in HS. We devised a strategy allowing linking two synthetic S fragments of HS through a spacer. To this aim we selected two click chemistry reactions: the "CuAAC" triazole formation and "oxime ligation". To implement this strategy, we optimized, on a disaccharide model derived from cellobiose, a methodology allowing the functionalization of the reducing and non-reducing end of synthetic oligosaccharides by to orthogonal reactive functions. Then we extended the methodology to a HS tetrasaccharide fragment. In this work, we optimized two key reactions: an anomeric alkylation in water and a hydroxyl allylation in neutral condition
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Estudo conformacional e estereoeletrônico de oximas de cicloexanonas α-heterossubstituídas e de seus éteres metílicos / Conformational study and stereoelectronic of oximes -heterossubstituídas cyclohexanones and their methyl ethersRibeiro, Douglas da Silva 27 October 1999 (has links)
As populações axial/equatorial em oximas e O-metiI oximas de 2-X-cicloexanonas (X= F, CI, Br, OCH3, SCH3 e N(CH3)2) foram efetivamente determinadas pela análise dos deslocamentos químicos dos prótons 6, utilizando-se os derivados da 4-tércio-butil-cicloexanona como modelos das conformações equatorial e axial. As populações dos confôrmeros axiais também foram determinadas pela análise dos deslocamentos químicos do carbono 4. Este carbono está em uma posição gama gauche em relação ao heteroátomo e sofre assim uma blindagem quando a conformação é axial. Usando-se os deslocamentos químicos observados do carbono 4 do isômero Z, foi possível calcular estas populações no isômero E. Os isômeros Z não apresentam este equilíbrio axial I equatorial porque existe uma compressão estérica grande entre o heteroátomo e o oxigênio na hipotética conformação equatorial. As populações axiais nestes compostos variam de 86% a 96% e apresentam uma dispersão muito pequena com os diferentes métodos utilizados. Ao se comparar oximas com éteres nota-se que para os substituintes mais polarizáveis, como metiltio, cloro e bromo há um aumento da população axial nos éteres comparado às oximas. As frequências de estiramento vCN se correlacionaram com os parâmetros indutivos de Taft (σl) e com a polarizabilidade média da ligação carbono-heteroátomo, o que apoia a idéia de uma interação πCN/σ*cx. Além disso, as frequências de estiramento vOH também se correlacionaram com estes parâmetros e neste caso o efeito indutivo e a polarizabilidade levam a um aumento de acidez destas oximas. / The axial/equatorial populations of oximes and O-methyl oximes of 2-X-cyclohexanones ((X= F, CI, Sr, OCH3, SCH3 e N(CH3)2) were determined by the chemical shifts of the protons bonded to carbon 6, making use of the 4-tert-butyl- cyclohexanone derivatives as models for the equatorial and axial conformations. The axial conformer populations were also determined by the C-4 chemical shift analysis. This carbon lies in a gamma gauche position to the heteroatom and suffers shielding when the conformation is axial. It has been possible to calculate those populations in the E isomer, using the C-4 chemical shift of the Z isomer. The latter do not present an axial/equatorial equilibrium because there is a too high steric compression between the nitrogen and the heteroatom in the hypothethical equatorial conformation. The axial populations of these compounds vary from 86 to 96% and present a small deviation along the different methods used. All substituents are preferentially in the axial conformation, even fluorine and methoxyl, which are predominantly equatorial in the corresponding ketones. It is noted that there is a increase in the axial population for more polarizable substituents like methylthio, chloro and bromo, on going from the oximes to the oximes O-methyl ethers. The vCN stretching frequencies are correlated with Taft\'s inductive parameters (σl) and the mean polarizability of the carbon-heteroatom bond, which supports the view of a πCN/σ*cx interaction. Sesides, the vOH stretching frequencies are also correlated with those parameters and in this case, both the inductive effect and polarizability lead to a increase of the oximes acidity.
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Estudo conformacional e estereoeletrônico de oximas de cicloexanonas α-heterossubstituídas e de seus éteres metílicos / Conformational study and stereoelectronic of oximes -heterossubstituídas cyclohexanones and their methyl ethersDouglas da Silva Ribeiro 27 October 1999 (has links)
As populações axial/equatorial em oximas e O-metiI oximas de 2-X-cicloexanonas (X= F, CI, Br, OCH3, SCH3 e N(CH3)2) foram efetivamente determinadas pela análise dos deslocamentos químicos dos prótons 6, utilizando-se os derivados da 4-tércio-butil-cicloexanona como modelos das conformações equatorial e axial. As populações dos confôrmeros axiais também foram determinadas pela análise dos deslocamentos químicos do carbono 4. Este carbono está em uma posição gama gauche em relação ao heteroátomo e sofre assim uma blindagem quando a conformação é axial. Usando-se os deslocamentos químicos observados do carbono 4 do isômero Z, foi possível calcular estas populações no isômero E. Os isômeros Z não apresentam este equilíbrio axial I equatorial porque existe uma compressão estérica grande entre o heteroátomo e o oxigênio na hipotética conformação equatorial. As populações axiais nestes compostos variam de 86% a 96% e apresentam uma dispersão muito pequena com os diferentes métodos utilizados. Ao se comparar oximas com éteres nota-se que para os substituintes mais polarizáveis, como metiltio, cloro e bromo há um aumento da população axial nos éteres comparado às oximas. As frequências de estiramento vCN se correlacionaram com os parâmetros indutivos de Taft (σl) e com a polarizabilidade média da ligação carbono-heteroátomo, o que apoia a idéia de uma interação πCN/σ*cx. Além disso, as frequências de estiramento vOH também se correlacionaram com estes parâmetros e neste caso o efeito indutivo e a polarizabilidade levam a um aumento de acidez destas oximas. / The axial/equatorial populations of oximes and O-methyl oximes of 2-X-cyclohexanones ((X= F, CI, Sr, OCH3, SCH3 e N(CH3)2) were determined by the chemical shifts of the protons bonded to carbon 6, making use of the 4-tert-butyl- cyclohexanone derivatives as models for the equatorial and axial conformations. The axial conformer populations were also determined by the C-4 chemical shift analysis. This carbon lies in a gamma gauche position to the heteroatom and suffers shielding when the conformation is axial. It has been possible to calculate those populations in the E isomer, using the C-4 chemical shift of the Z isomer. The latter do not present an axial/equatorial equilibrium because there is a too high steric compression between the nitrogen and the heteroatom in the hypothethical equatorial conformation. The axial populations of these compounds vary from 86 to 96% and present a small deviation along the different methods used. All substituents are preferentially in the axial conformation, even fluorine and methoxyl, which are predominantly equatorial in the corresponding ketones. It is noted that there is a increase in the axial population for more polarizable substituents like methylthio, chloro and bromo, on going from the oximes to the oximes O-methyl ethers. The vCN stretching frequencies are correlated with Taft\'s inductive parameters (σl) and the mean polarizability of the carbon-heteroatom bond, which supports the view of a πCN/σ*cx interaction. Sesides, the vOH stretching frequencies are also correlated with those parameters and in this case, both the inductive effect and polarizability lead to a increase of the oximes acidity.
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Synthèse d'une librairie d'analogues monomériques et dimériques du sLe XCalosso, Mickael 09 1900 (has links)
Dans cet ouvrage sera décrite la synthèse de nouveaux analogues du sialyl
Lewis X (sLex). A cet effet, nous avons préparé une librairie d’analogues synthétisée
à partir d’une approche mettant en jeu un «espaceur» acyclique permettant d’avoir un
biais conformationnel que nous avons défini comme la stratégie ATC-B.
Nous avions déjà démontré que certains analogues portant un groupe benzoate
en C-2 et en C-4 du galactose présentent une activité 50 fois supérieure à celle du
sLex. Nous avions par ailleurs démontré qu’en l’absence du benzoate en C-2,
l’activité devient alors trois fois plus faible. A présent, il paraissait interessant de
synthétiser des analogues ayant seulement un groupe benzoate en C-4 pour evaluer
l’impact de ce groupement sur la puissance de nos analogues.
Par le passé, nous avions également mis en évidence le rôle des esters sur
l’activité des analogues portant un «espaceur» acyclique dans le cadre de la stratégie
ATC-B. Nous effectuerons donc des variations à ce niveau pour en évaluer l’impact.
Enfin, nous avons préparé une nouvelle famille d’analogues de type dimère.
Ceux-ci seront constitués de 2 unités des composés monomériques synthétisés
précédemment. La synthèse de ces dimères fera l’emploi de la «Click Chemistry».
Cette étude nous mènera a vous présenter la synthèse de ces composés et la
méthodologie employée. / This work describes the synthesis of novel sialyl Lewis X (sLex) analogues.
To this end, we have prepared a library of analogues by implementing a strategy that
makes use of an Acyclic Tether which allows for defined Conformational Bias (ATCB
strategy).
We have previously shown that analogues bearing a benzoate group at both
positions C-2 and C-4 of the galactose exert an activity 50-fold greater than that of
sLex. Indeed, removing the benzoate at position C-4 while keeping the one at C-2 led
to a three fold decrease in potency. We are currently preparing the corresponding
analogues that have the benzoate only at position C-4 in order to fully evaluate its
impact on the potency of the analogue.
We have also previously elucidated the role of esters on the activity of
analogues that have acyclic tether as part of the ATC-B strategy. Variations have
been made at the level of the ester and their impact has been evaluated.
Lastly, we have prepared a novel family of analogues consisting of two
identical monomeric subunits linked together. Synthesis of these dimers was
performed via «Click Chemistry». This study describes the synthesis of the
compounds and the methodology employed.
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Addition stéréosélective de nucléophiles sur un centre acétal : synthèse de nucléosides 1’,2’-cisSt-Jean, Olivier 04 1900 (has links)
Plusieurs analogues de nucléosides thérapeutiques (Ara-C, Clofarabine), utilisés
pour le traitement de leucémies, présentent un arrangement 1’,2’-cis entre la nucléobase
reliée au centre anomère et le substituant (électroattracteur) en C-2’. Récemment, notre
laboratoire a développé une approche synthétique pour former sélectivement des
analogues de nucléosides et de thionucléosides 1’,2’-trans et 1’,2’-cis à partir de
précurseurs acycliques.
Ce mémoire présente une nouvelle méthodologie pour accéder efficacement aux
analogues de nucléosides 1’,2’-cis à partir de furanosides. Différents groupements en
position anomérique ont été examinés, sous conditions cinétiques en utilisant le bromure
de diméthylbore pour générer sélectivement des produits acycliques ou cycliques. Les
intermédiaires cinétiques de différents furanosides de méthyle formés en présence de
Me2BBr ont été piégés in situ par un thiol pour générer des thioacétals acycliques avec
de bonnes voire d’excellentes diastéréosélectivités. Les produits générés sont en accord
avec une rétention globale de l’information stéréochimique du centre acétal et deux
déplacements SN2 consécutifs ont été suggérés pour rationaliser ces résultats. Toutefois,
l’objectif de synthétiser des analogues de nucléosides à partir de furanosides de méthyle
a échoué.
Tel que démontré par le Dr Michel Prévost, l’activation par Me2BBr des lactols
des quatres différents furanosides suivie d’une addition in situ d’une base silylée a
permis de former diastéréosélectivement les analogues de nucléosides 1’,2’-cis
correspondants avec d’excellents rendements. Nous avons démontré que d’autres
substrats peuvent être employés et que l’induction stéréochimique est sous contrôle du
substituant électroattracteur en C-2. D’autres acides de Lewis, tel que TMSBr, peuvent
également être utilisés.
Cette méthodologie a également été étendue à d’autres nucléophiles tels que des
Grignards ou des éthers d’énols silylés, conduisant à de bonnes sélectivités. / Many therapeutically relevant nucleoside analogs (Ara-C, Clofarabine) for the
treatment of leukemia have a 1’,2’-cis arrangement between the nucleobase attached at
the anomeric center and the non-hydrogen substituent at C-2’. Recently, our laboratory
has developed a versatile approach to the synthesis of 1’,2’-trans and 1’,2’-cis
nucleoside and thionucleoside analogues from acyclic scaffolds.
This work will present a new methodology to access efficiently 1’,2’-cis
nucleoside analogues from cyclic furanoside. Activation of various anomeric groups by
Me2BBr was investigated, and under kinetic control acyclic substrates or cyclic ones
could be generated selectively. Trapping the kinetic product of methyl furanoside
formed in presence of Me2BBr by thiol in the presence of base led to the formation of
acyclic thioacetal in good to excellent diastereoselectivity. The results obtained are in
accordance with total retention of the stereochemical information of the acetal moiety
and thus suggested that the mechanism of these two reactions is two successive SN2
displacements. The objective of synthesizing nucleoside analogs from methyl
furanoside was unsuccessful.
As shown recently by Dr Michel Prévost, activation of all four furanoside lactol
scaffolds by Me2BBr with an in situ addition of silylated nucleobase afforded 1’,2’-cis
pyrimidine nucleoside analogues in very good yields and with diastereoselectivities
greater or equal to 20:1. Expending this methodology to other scaffolds provided
evidence of stereoelectronic control of the C-2 electron-withdrawing substituent. Other
Lewis acids such as TMSBr can be used.
This methodology was also applied to other nucleophiles such as allyl Grignard
and silylated enols ethers, which were successfully alkylated in good yield and 1,2-cis
diastereoselectivity.
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