Synthesis, NMR, and conformational studies of fucoidan fragments.: V.: Linear 4,4′,4"-Tri-O-sulfated and parent non-sulfated (1→3)-fucotrioside fragments

Propyl 4,4',4"-tri-O-sulfated and non-sulfated (1 --> 3)-alpha-L-fucotriosides which are related to fragments of natural fucoidans have been synthesized. Their spectral and conformational properties have been investigated by H-1 and C-13 NMR, NOE and molecular modeling. Molecular mechanics calculations of the tri-O-sulfated compound as a trianion did not give agreement with the experimental NOE values, while the model with the non-dissociated sulfo group on the non-reducing end worked successfully. (1 --> 3)-Fucobioside fragments in both trisaccharides investigated were shown to have the same range of conformations as in previously described propyl (1 --> 3)-alpha-L-fucobiosides, but with the increase of the relative population of the conformer with the spatial proximity of H-1' and H-4 in the case of non-sulfated fucotrioside.