Synthesis, NMR, and Conformational Studies of Fucoidan Fragments. VII.1 Influence of Length and 2,3‐Branching on the Conformational Behavior of Linear (1→3)‐Linked Oligofucoside Chains

The conformational behavior of linear (1→3)‐linked propyl di‐, tri‐, tetrafucosides and 2,3‐branched tetrafucosides with linear (1→3)‐linked trisaccharide backbone related to fragments of natural fucoidans were studied by theoretical molecular modeling and experimental determination of transglycosidic vicinal coupling constants 3JC,H. The application of NOE NMR‐spectroscopy, which is traditionally used in conformational analysis of oligosaccharides, was accompanied by experimental difficulties in the case of tetrafucosides, due to the overlap of cross‐peaks and their trend to be close to zero. It was shown that conformations of difucoside units in the studied compounds depend on their position within the oligosaccharide backbone, on the chain length, and on the presence or absence of 2,3‐branch point. The comparison of experimental and calculated values of transglycosidic constants 3JC,H showed good coincidence for the middle disaccharide units of tetrafucosides, indicating that these units are more rigid than terminal ones.

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