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Relative reactivities in the O-methylation of glucomannans: the influence of stereochemistry at C-2 and the solvent effect
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.ORCID iD: 0000-0002-2900-4713
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Technische Universität Braunschweig, Germany .
2015 (English)In: Carbohydrate Research, ISSN 0008-6215, E-ISSN 1873-426X, Vol. 402, 172-179 p.Article in journal (Refereed) Published
Abstract [en]

The main hemicellulose in softwood, glucomannan (GM), structurally resembles cellulose but has quite different physical and chemical properties. In addition to branching and original acetylation, the only other difference between these two beta-1,4-linked glycans is the configuration at C-2 in approximately 80% of the sugar residues. In contrast to glucose, the 2-OH in mannose has an axial orientation. The influence of this stereochemistry on the relative reactivities of glucosyl compared to mannosyl units in methylation reactions are studied in this work. Glucomannan isolated from spruce (SGM) and commercially available konjac glucomannan (KGM) was methylated in DMSO/Li-dimsyl/MeI and water/NaOH/MeI system, respectively. In the early stage of the reaction, the glucose part of the SGM achieved slightly higher DS values than the mannose residues, but the overall relative rate constants were close to 1:1. The order of reactivities in glucose was k(2) > k(3) > k(6) and k(3) > k(2) > k(6) for mannose (in DMSO/Li-dimsyl/MeI). The rate constants did not remain constant, but k(3) decreased when k(2) increased for both epimeric sugars. In water/NaOH/MeI, the methylation of the primary 6-OH was much more pronounced with an order of reactivity of O-6 > O-2 > O-3 for mannose and O-2 > O-6 > O-3 for glucose. The results are discussed with respect to the OH-acidity and the stereoelectronic, sterical, and solvent effects.

Place, publisher, year, edition, pages
2015. Vol. 402, 172-179 p.
Keyword [en]
Spruce glucomannan, Relative reactivities, Partial methylation, Solvent effect
National Category
Biochemistry and Molecular Biology
Identifiers
URN: urn:nbn:se:kth:diva-159350DOI: 10.1016/j.carres.2014.06.005ISI: 000346825800022Scopus ID: 2-s2.0-84919691742OAI: oai:DiVA.org:kth-159350DiVA: diva2:785113
Note

QC 20150202

Available from: 2015-02-02 Created: 2015-01-29 Last updated: 2017-12-05Bibliographically approved

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Zhang, YujiaLindström, Mikael E.

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