SYNTHESIS, NMR-SPECTROSCOPY AND CONFORMATIONAL STUDIES OF 2 VICINALLYDISUBSTITUTED TRISACCHARIDES

Two trisaccharides with 2,3-vicinal disubstitution have been synthesiz ed and analysed by NMR spectroscopy and Monte Carlo simulations. When vicinal disubstitution occurs in trisaccharides, experimental NMR spec tra often differ significantly from those calculated by simple additiv ity schemes. In the present study, small deviations from additivity oc curred for the carbons at the glycosylation positions of the disubstit uted sugar residues in -D-Glcp(1-->2)[beta-D-Glcp(1-->3)]alpha-D-Glcp- OMe (1) and -D-Glcp(1-->2)[beta-D-Glcp(1-->3)]alpha-D-Manp-OME (2). Mo nte Carlo simulations, using the HSEA force held, showed a change in t he average values and in the rms fluctuations of the psi-dihedral angl es of 2 compared to the corresponding disaccharides, whereas for 1 sma ller changes were observed.