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Chair interconversion and reactivity of mannuronic acid esters
Stockholm University, Faculty of Science, Department of Organic Chemistry.
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2013 (English)In: Organic and biomolecular chemistry, ISSN 1477-0520, E-ISSN 1477-0539, Vol. 11, no 46, 8127-8134 p.Article in journal (Refereed) Published
Abstract [en]

Mannopyranosyluronic acids display a very unusual conformation behavior in that they often prefer to adopt a C-1(4) chair conformation. They are endowed with a strikingly high reactivity when used in a glycosylation reaction as a glycosyl donor. To investigate the unusual conformational behavior a series of mannuronic acid ester derivatives, comprising anomeric triflate species and O-methyl glycosides, was examined by dynamic NMR experiments, through lineshape analysis of H-1 and F-19 NMR spectra at various temperatures from -80 degrees C to 0 degrees C. Exchange rates between C-4(1) and C-1(4) chair conformations were found to depend on the electronic properties and the size of the C2 substituent (F, N-3 or OBn) and the aglycon, with higher exchange rates for the glycosyl triflates and smaller C2 substituents. Low temperature F-19 exchange spectroscopy experiments showed that the covalently bound anomeric triflates did not exchange with free triflate species present in the reaction mixture. To relate the conformational behavior of the intermediate triflates to their reactivity in a glycosylation reaction, their relative reactivity was determined via competition reactions monitored by H-1 NMR spectroscopy at low temperature. The 2-O-benzyl ether compound was found to be most reactive whereas the 2-fluoro compound - the most flexible of the studied compounds - was least reactive. Whereas the ring-flip of the mannuronic acids is important for the enhanced reactivity of the donors, the rate of the ring-flip has little influence on the relative reactivity.

Place, publisher, year, edition, pages
2013. Vol. 11, no 46, 8127-8134 p.
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-98249DOI: 10.1039/c3ob41747fISI: 000327682400018OAI: oai:DiVA.org:su-98249DiVA: diva2:683288
Note

AuthorCount:5;

Available from: 2014-01-03 Created: 2014-01-03 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Structure, dynamics and reactivity of carbohydrates: NMR spectroscopic studies
Open this publication in new window or tab >>Structure, dynamics and reactivity of carbohydrates: NMR spectroscopic studies
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis is on the ring conformations of carbohydrate molecules; how the conformational equilibria and the rates of the associated interconversions are affected by the molecular constitution and their surroundings.

The conformational equilibria of a group of amine linked pseudodisaccharides, designed as potential glycosidase inhibitors, comprising α-D-altrosides are described in Chapter 3. The OS2 conformation was largely populated, and the ring conformation was found to depend on the charge of the amine functionality.

The conformations of β-D-xylopyranoside derivatives with naphthyl-based aglycones, which are potential anti-cancer agents, are described in chapter 4. Solvent dependent flexibility was observed. Intramolecular hydrogen bonds were concluded to be involved in the stabilization of 1C4 conformers in non-hydrogen bonding solvents of low polarity.

Chapter 5 describes the first measurements of the conformational exchange rates of mannuronic acid ester derivatives between the 4C1 and 1C4 conformations, through DNMR measurements. The relative reactivity of glycosyl triflates as electrophiles in glycosylation reactions were investigated with NMR-based competition experiments.

In Chapter 6, investigations of ruthenium-catalyzed epimerizations of the allylic alcohols of glycal derivatives, and stereoselective synthesis of esters through a DYKAT protocol, are described. The kinetics of the epimerizations were elaborated through different NMR-spectroscopic methods.

Chapter 7 describes additions of NMR chemical shift data of mono- and oligosaccharides to database of the computer program CASPER, and applications thereof.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2013. 67 p.
Keyword
Carbohydrates, Conformation, NMR spectroscopy, Hydrogen bond
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-92408 (URN)978-91-7447-730-6 (ISBN)
Public defence
2013-09-20, Magnélisalen, Kemiska Övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Submitted. Paper 5: Manuscript.

Available from: 2013-08-29 Created: 2013-08-02 Last updated: 2016-04-11Bibliographically approved

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