Comprehensive analysis of the substitution pattern in dextran ethers with respect to the reaction conditions

Abstract

Dextrans from Leuconostoc ssp., alpha-1,6-linked glucans branched at O-3, were O-methylated in DMSO with lithium dimsyl and methyl iodide under various conditions. Methyl substituent distribution was comprehensively studied in the terminal, internal, and branched glucosyl units and along and over the dextran macromolecules. The order of reactivity was O-2 > O-4 > or = O-3. The methyl pattern in the glucosyl units significantly deviates from a random distribution with enhanced amounts of un- and trisubstituted moieties. This deviation was found to proceed on macromolecular level by means of ESI-MS of perdeuteromethylated and partially depolymerized methyl dextrans. Heterogeneity was much more pronounced than for methyl amylose prepared under comparable conditions. DS gradients in and over the material are discussed with respect to dextran structure and the mechanism of Li dimsyl alkylation. For comparison, cyanoethyl dextrans were prepared by sodium hydroxide catalyzed addition of acrylonitrile. Monomer analysis of cyanoethyl dextrans revealed that this thermodynamically controlled reaction gave a random substitution pattern with 48% of cyanoethyl groups at O-2, 33% at O-4, and 19% at O-3.

Nanoparticles of alkylglyceryl-dextran-graft-poly(lactic acid) for drug delivery to the brain: Preparation and in vitro investigation

“…The degree of substitution varied widely (from 0.7% to 75.1% for DEX-OX4, and from 16.5% to 38.2% for DEX-OX8), and it was found to increase with reaction time and with the concentration of base (t-BuOK) employed. Since the calculated degree of substitution never exceeded 100%, and considering that the OH group reactivity in dextran towards alkylation agents is known to decrease in the order C2 > C4 > C3 (likely due to the proximity to the anomeric C1 carbon) [32][33][34][35], it can be reasonably assumed that only the primary hydroxy groups were grafted with alkylglyceryl chains.…”

Alkynyl Ethers of Glucans: Substituent Distribution in Propargyl‐, Pentynyl‐ and Hexynyldextrans and ‐amyloses and Support for Silver Nanoparticle Formation

“…Methylation of dextrans with Li-dimsyl/MeI also showed pronounced heterogeneity, increasing with amount of base. [18] …”

“…Heterogeneity is not only the result of selective Pg losses during hydrolysis, but is also observed after methanolysis and also for methyldextrans prepared under similar conditions. [18] Higher Homologs of Propargyl Ethers: O-Pentynyland O-Hexynyldextrans (HyDs)…”

“…[17] We have recently reported on model studies of methyldextrans. [18] How important the pattern of substitution is with respect to properties, is well known from the field of starch and cellulose derivatives. [19] Alkynyl ethers of polysaccharides are interesting products themselves and also as intermediates to introduce a number of further functionalities.…”

Effect of structurally different microbial homoexopolysaccharides on the quality of gluten-free bread

“…Permethylated dextrans were then submitted to methanolysis and trimethylsilylation as described by Vollmer et al [23].…”