Synthesis, NMR, and Conformational Studies of Cyclic Oligo‐(1→6)‐β‐D‐Glucosamines

Abstract

The first synthesis of a series of homologous cyclic oligo‐(1→6)‐β‐D‐glucosamines consisting of two to seven residues and representing a new type of functionalized cyclic oligosaccharides is reported. Remarkably high yields of the studied macrocyclization reaction irrespective of the length of the acyclic precursors were observed. In the case of compounds constituted of four to seven glucosamine units α‐stereoisomers formed as side products despite the presence of a strongly participating 2‐N‐phthaloyl group to control β‐glycosylation. Both phenomena may be accounted for by conformational features of the linear bifunctional precursors. According to computer modeling and NMR conformational studies, the described linear (1→6)‐β‐linked oligoglucosamines exist in a right‐handed helix‐like conformation, in which the glycosyl donor and acceptor moieties are prearranged in a way that facilitates intramolecular glycosylation from the α‐side. Prepared cyclo‐oligoglucosamines differ in their conformational flexibilities, as illustrated by their spectral characteristics and calculated asphericity distributions. Moreover, the obtained compounds do not possess a distinct hydrophobic cavity, which is in contrast to the well‐known cyclodextrins. All these characteristics provide an excellent basis for the use of these novel cyclic oligosaccharides as scaffolds for the construction of biomolecular conjugates.

Organogel–quantum dots hybrid materials displaying fluorescence sensitivity and structural stability towards nitric oxide

“…reacting ends of the open-chain precursor [12][13][14][15][16][17]. In this regard, anions can act as an external stimulus.…”

NMR and conformational studies of linear and cyclic oligo-(1→6)-β-d-glucosamines

“…7–9 Analysis of integral intensities in 1 H NMR spectra of these compounds showed that in the case of cyclic oligosaccharides 7a–12a the stoichiometric salts were formed with one molecule of acetic acid per each amino group. In the case of linear di- ( 1a ), tri- ( 2a ) and tetrasaccharide ( 3a ) acetate ions were also present in stoichiometric ratio to amino groups, while in penta- ( 4a ) and heptasaccharide ( 6a ) only four acetates were present.…”

“…Preliminary results from the conformational study of the cyclic glucosamines was reported previously; 9 herein these compounds are investigated in more detail and in comparison with corresponding linear oligosaccharides. Their study is of special interest due to the structural relationship between cycloglucosamines and cyclodextrins.…”

“…1) oligoglucosamines and their corresponding N-acetylated derivatives 1b–12b . Synthesis of these compounds has been described 7–9 and some of them have been documented to induce formation of protective antibodies in animals when conjugated to carrier proteins. 10 These oligosaccharides differ from each other by a number of structural factors such as the presence of N-acetyl groups, cyclization and elongation of the oligosaccharide chains which may drastically influence the biological activity in relation to biofilm formation and vaccine potential.…”

“…13 The presence of amino groups along with the central cavity in the studied oligosaccharides provides the possibility to modify and possibly extend their ability to form complex structures. Apart from our own previous publication 9 , only one work 14 is known to us that describes the conformational analysis of (1→6)-linked oligosaccharides that consist of three or more monosaccharide residues.…”