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Experimental Evidence for the Existence of Non‐ exo ‐Anomeric Conformations in Branched Oligosaccharides: NMR Analysis of the Structure and Dynamics of Aminoglycosides of the Neomycin Family
Author(s) -
Asensio Juan Luis,
Hidalgo Ana,
Cuesta Igor,
González Carlos,
Cañada Javier,
Vicent Cristina,
Chiara Jose Luis,
Cuevas Gabriel,
JiménezBarbero Jesús
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021115)8:22<5228::aid-chem5228>3.0.co;2-l
Subject(s) - anomer , chemistry , glycosidic bond , stereochemistry , anomeric effect , biochemistry , enzyme
It is commonly known that the exo‐ anomeric effect is a major factor governing the conformational behavior of naturally occurring oligosaccharides. Conformational flexibility in these molecules mainly concerns the aglycon ψ angle since ϕ is restricted by this stereoelectronic effect. In fact, to the best of our knowledge no case of a natural glycoside adopting a non ‐exo‐ anomeric conformation in solution has yet been reported. With respect to the flexibility among naturally occurring carbohydrates, branched type oligosaccharides including sugar residues glycosidated at contiguous positions (such as blood type carbohydrate antigens Lewis X) have been considered as the paradigm of rigid saccharides—the rigidity being enhanced by van der Waals interactions. Herein, we demonstrate unambiguously that both common beliefs are not to be generalized. For example in neomycin B, a branched oligosaccharide antibiotic, a large number of non ‐exo‐ anomeric conformations was detected in solution for the first time in naturally occurring sugars. This unusual behavior is attributed to branching. Here, polar contacts between non‐vicinal sugar units lead to an enhanced flexibility of the ribose glycosidic torsion ϕ . The influence of sugar flexibility on RNA recognition will also be discussed.