title: 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.
abstract: 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 psi angle since phi is restricted by this stereo-electronic 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 phi. The influence of sugar flexibility on RNA recognition will also be discussed.
authors.affiliation: Instituto de Química Orgánica, CSIC Juan de la Cierva 3, 28006 Madrid, Spain.
authors.forename: Juan Luis
authors.initials: JL
authors.lastname: Asensio
authors.forename: Ana
authors.initials: A
authors.lastname: Hidalgo
authors.forename: Igor
authors.initials: I
authors.lastname: Cuesta
authors.forename: Carlos
authors.initials: C
authors.lastname: González
authors.forename: Javier
authors.initials: J
authors.lastname: Cañada
authors.forename: Cristina
authors.initials: C
authors.lastname: Vicent
authors.forename: Jose Luis
authors.initials: JL
authors.lastname: Chiara
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cuevas
authors.forename: Jesús
authors.initials: J
authors.lastname: Jiménez-Barbero
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000378:metabolism; D002236:Carbohydrate Conformation; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D009355:Neomycin / Q000737:chemistry* / Q000378:metabolism; D009844:Oligosaccharides / Q000737:chemistry* / Q000378:metabolism; D018583:Pliability; D012335:RNA, Ribosomal / Q000378:metabolism; D012266:Ribose / Q000737:chemistry / Q000378:metabolism; D012271:Ribostamycin / Q000737:chemistry / Q000378:metabolism; D012996:Solutions
chemical_list: D000900:Anti-Bacterial Agents; D009844:Oligosaccharides; D012335:RNA, Ribosomal; D012996:Solutions; D012271:Ribostamycin; D012266:Ribose; D009355:Neomycin