6,687 research outputs found
TACC3-ch-TOG track the growing tips of microtubules independently of clathrin and Aurora-A phosphorylation
No full textThe interaction between TACC3 (transforming acidic coiled coil protein 3) and the microtubule polymerase ch-TOG (colonic, hepatic tumor overexpressed gene) is evolutionarily conserved. Loading of TACC3–ch-TOG onto spindle microtubules requires the phosphorylation of TACC3 by Aurora-A kinase and the subsequent interaction of TACC3 with clathrin to form a microtubule binding surface. Whether there is a pool of TACC3–ch-TOG that is independent of clathrin in human cells, and what is the function of this pool, are open questions. Here, we report that TACC3 is recruited to the plus-ends of microtubules by its association with ch-TOG and that this pool is independent of phosphorylation and binding to clathrin. The plus-end binding of TACC3–ch-TOG persists in interphase and we propose that one cellular function of TACC3–ch-TOG is to modulate cell migration. We also describe the distinct subcellular pools of TACC3, ch-TOG and clathrin. TACC3 is often described as a centrosomal protein, but we show that there is no significant population of TACC3 at centrosomes. The delineation of distinct protein pools reveals a simplified view of how these proteins are organized and controlled by post-translational modification
The synthesis of natural and novel glucosinolates
No full textThis thesis describes the synthesis of natural and novel glucosinolates 1.Chapter 1 gives an overview of glucosinolates, from isolation and biosynthesis
to previous chemical syntheses. Chapter 2 describes an improved method for
the formation of thiohydroximate bonds and its application over a variey of
substrates. Chapter 3 focuses on exploring new chemistry on intact glucoinolates and details oxidative chemistry on an alkene containing side chain glucosinolate. Futhermore, the total synthesis of novel glucosinolates 150, 156 and 161 is illustrated.Chapter 4 describes a model study for the solid phase synthesis of
glucosinolates. Finally experimental procedures for the compounds synthesised
in the thesis are described in Chapter 5
Novel methodology for the synthesis of ¹³C-Labelled phenols and its application to the total synthesis of polyphenols
No full textElectronic redacted version does not contain associated previously published materialThe base-catalysed reaction of 4H-pyran-4-one with a range of nucleophiles, namely diethyl malonate, ethyl acetoacetate, nitromethane, acetylacetone and ethyl cyanoacetate, was developed as a reliable, high yielding method for the preparation of para-substituted phenols.
The methodology was extended to include the use of the substituted pyranones, maltol, 2,6-dimethyl-4H-pyran-4-one and diethyl chelidonate. Reactions were studied using conventional heating methods and microwave irradiation. Microwave irradiation had definite beneficial effects, with improved yields, reduced reaction times and cleaner reaction profiles.
The potential of this methodology was examined for the regioselective placement of ¹³C-atoms into benzene rings using ¹³C-labelled nucleophiles or ¹³C-labelled 4H-pyran-4-ones. [3,5-13C₂]4H-Pyran-4-one and [2,6-13C₂]4H-pyran-4-one were prepared from various ¹³C-labelled versions of triethyl orthoformate and acetone. This methodology was applied to the synthesis of
[1,3,5-¹³C₃]gallic acid, via the base-catalysed reaction of [3,5-¹³C₂]4H-pyran-4-one with diethyl [2-¹³C]malonate, followed by subsequent transformations to yield [1,3,5-¹³C₃]gallic acid.
The preparation of [2-¹³C]phloroglucinol was carried out via [2-¹³C]resorcinol, with
regioselective placement of a single ¹³C-atom into the aromatic ring. This was accomplished from non-aromatic precursors, with the source of the ¹³C-atom being [¹³C]methyl iodide. The key step in this synthesis was the introduction of the third hydroxyl group, which was achieved using a modified iridium-catalysed C-H activation/borylation/oxidation procedure. The scope of an existing C-H activation/borylation reaction was modified and expanded to include a range of protected resorcinol derivatives. A catalyst system was developed which allowed high conversion to the intermediate arylboronic acids, followed by oxidation using aqueous Oxone®
to yield the corresponding phenols.
Finally, to demonstrate the potential of these new methods for application in the synthesis of isotopically labelled natural products and polyphenols, the syntheses of ¹³C-labelled anthocyanins were studied. A route was developed that could be applied to the synthesis of either cyanidin-3-glucoside or delphinidin-3-glucoside. Only the final coupling/cyclisation step to yield the desired anthocyanin targets remains to be carried out
Studies on the synthesis of dicaffeoylquinic acid conjugates
No full textDicaffeoylquinic acid (DCQA) is a natural polyphenolic compound widely distributed in plants such as coffee beans, which possesses a range of pharmacological activities. Herein, is reported studies undertaken towards the first total synthesis of 3,5-DCQA conjugates. Two synthetic routes were investigated. The first route involves a seven step sequence beginning from quinic acid. The overall yield via this synthetic approach was 30%. The key steps involved in the sequence were a regioselective benzylation of the C-3-hydroxyl group followed by silyl protection of the C-1 and C-4 hydroxyl groups. Deprotection of the benzyl group by hydrogenolysis and opening of the lactone afforded the 3,5-diol. Esterification of the 3,5-diol with 3,4-tert-butyldimethylsilyl caffeoyl chloride afforded the di-ester. Removal of the protecting groups afforded 3,5-DCQA. The second route involved selective protection of the C-3-hydroxyl group with silyl followed by benzylation of the C-1 and C-3 hydroxyl groups. Saponification of the lactone ring followed by benzylation of the carboxylic acid gave the benzyl ester. Silyl deprotection afforded the 3,5-diol. The 3,5-diol was subsequently esterified by refluxing in toluene with commercially available Meldrum’s acid. In the final step, the synthesis of 3,5-DCQA was achieved by a Knoevenagel condensation of 3,4-dihydroxybenzaldehyde and a malonate ester of quinic acid. An efficient method for the synthesis of possible metabolites of quinic acid conjugates was also described. This protocol employs N-(4-methoxyphenyl)-trifluoroacetimidate glucuronyl as the donor. The key reaction in this sequence was the coupling of N-(4-methoxyphenyl)-trifluoroacetimidate glucuronyl with 4-hydroxy-3-methoxy-benzaldehyde
Les diminutifs basques avec ch
No full textSe presentan formaciones similares a los diminutivos vascos con "ch" en España y América latina. Se dan ejemplosThe author introduces similar formations to the Basque diminutive "ch" in Spain and Latin America. Examples are provide
COUPLING OF THE C-H STRETCH TO LARGE-AMPLITUDE TORSION AND INVERSION MOTIONS: COMPARISON OF CHCH, CHOH AND CHNH
No full textAuthor Institution: Department of Polymer Science and Department of Chemistry, The University of Akron; Department of Chemistry, The University of Akron, OH 44325In each of the title molecules, torsional and inversion tunneling occurs between six equivalent minima. Coupling of these degrees of freedom to the CH stretch occurs via variation of the C-H stretching force constants as a function of the torsional () and inversion () angles. Maps of the couplings have been computed at the MP2/6-311++G(3df,2p) level. Both the single bond CH stretch force constants and the bilinear couplings between CH bonds are presented as a function of and . Although the torsional barriers differ by more than a factor of 20, the torsion-inversion-vibration coupling patterns are very similar for CHNH and CHCH. On the other hand, the torsion-inversion-vibration coupling in the charged species CHOH is much weaker
Reply to the Ch. Lagrange’s note
No full textThe author answers to a Ch. Lagrange’s note who refutes his theory on the diurnal nutation.L’auteur répond à une note de Ch. Lagrange qui réfute sa théorie sur la nutation diurne
NATURE OF TORSION-INVERSION COUPLING IN CHNH, CHOH AND CHCH
No full textAuthor Institution: Department of Chemistry, The University of Akron, OH; 44325-3601Two-dimensional torsion-inversion surfaces for methylamine, protonated methanol and ethyl radical were calculated and fit to a function containing a polynomial in the inversion angle() and trigonometric functions of the torsional angle(). Calculations were done at the B3LYP, MP2, and CCSD(T) levels with the 6-311++G(d,p) and 6-311++G(3df, 2p) basis sets and partial optimization. CHNH, CHOH and CHCH have G symmetry with 6-equivalent minima which are located by the various calculations at inversion angles 6.5 to 11; 42 to 45.5 and 52.5 to 55 degrees respectively on either side of planar. The three molecules have very different barriers to inversion ranging from no barrier for CHCH to 838 cm for CHOH to 1837 cm for CHNH. The dominant torsion-inversion coupling term in all cases has the form
Note about Mr. Ch. Lagrange’s recent communication
No full textThe author establishes a note about Mr. Ch. Lagrange’s communication on the Eulerian nutation period.L’auteur établit une note au sujet d’une communication de Ch. Lagrande sur la période de la nutation eulérienne
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Using δ¹³C-CH₄ and δD-CH₄ to constrain Arctic methane emissions
No full text© Author(s) 2016.We present a global methane modelling study assessing the sensitivity of Arctic atmospheric CH₄ mole fractions, δ¹³C-CH₄ and δD-CH₄ to uncertainties in Arctic methane sources. Model simulations include methane tracers tagged by source and isotopic composition and are compared with atmospheric data at four northern high-latitude measurement sites. We find the model's ability to capture the magnitude and phase of observed seasonal cycles of CH₄ mixing ratios, δ¹³C-CH₄ and δD-CH₄ at northern high latitudes is much improved using a later spring kick-off and autumn decline in northern high-latitude wetland emissions than predicted by most process models. Results from our model simulations indicate that recent predictions of large methane emissions from thawing submarine permafrost in the East Siberian Arctic Shelf region could only be reconciled with global-scale atmospheric observations by making large adjustments to high-latitude anthropogenic or wetland emission inventories
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