Synthesis, NMR spectroscopy and conformational studies of two vicinally disubstituted trisaccharides

Abstract

Two trisaccharides with 2,3-vicinal disubstitution have been synthesized and analysed by NMR spectroscopy and Monte Carlo simulations. When vicinal disubstitution occurs in trisaccharides, experimental NMR spectra often differ significantly from those calculated by simple additivity schemes. In the present study, small deviations from additivity occurred for the carbons at the glycosylation positions of the disubstituted sugar residues in β-D-Glcp(1→2)[β-D-Glcp(1→3)]α-D-Glcp-OMe (1) and β-D-Glcp(1→2)[β-D-Glcp(1→3)]α-D-Manp-OMe (2). Monte Carlo simulations, using the HSEA force field, showed a change in the average values and in the rms fluctuations of the ψ-dihedral angles of 2 compared to the corresponding disaccharides, whereas for 1 smaller changes were observed.