Synthesis and conformational analysis of the T-antigen disaccharide (β-D-Gal-(1→3)-α-D-GalNAc-OMe)

We report an improved synthesis of the T-antigen disaccharide [β-D-Gal-(1→)-α-D-GalNAc-OMe], incorporating recycling of the undesired β-glycosyl acceptor [methyl 2-azido-4,6-benzylidene-2-deoxy-β-D-galactopyranoside (9β)] through anomerization by treatment with FeCl₃. The conformational analysis of the disaccharide made use of high quality NOE data in combination with extensive Metropolis Monte-Carlo (MMC) and molecular dynamic (MD) simulations. To sample the conformational space sufficiently, 9.5-10⁶ Monte-Carlo steps were collected for the MMC simulations, while the fully solvated MD simulations were performed for 10 ns for comparison. In general, the MMC and MD simulations agreed very well. Comparison of theoretical NOE curves from both MMC and MD simulations with the experimental curves showed that the disaccharide populates two regions of conformational space, with a population of about 95% for the global minimum energy region and about 5% for a local minimum energy region.