Syntheses of model oligosaccharides of biological significance. X.•Syntheses and NMR and mass spectral analysis of trideuteriomethyl di-3,6-O-(4-O-β-D-galactopyranosyl-2-acetamido-2-deoxy-β-D-glucopyranosyl)-β-D-galactopyranoside: the I antigen branchpoint penta- and tetrasaccharides and a related t

As part of our studies of complex oligosaccharides, in particular their three-dimensional structure, we have synthesized the antigen I branchpoint penta- and tetrasaccharides. The unbranched trisaccharide 3D was also synthesized, and its derivative 3B served as the intermediate for the synthesis of higher oligosaccharides. NMR spectra of major intermediates as well as of the final oligosaccharides were completely assigned. Mass spectra of the synthetic intermediates and the final oligosaccharides were analyzed and compared with those of a similar group of oligosaccharides containing L-fucose, N-acetyl-D-glucosamine, and D-galactose. Certain observations were made that could be utilized in the interpretation of mass spectra for the structural determination of protected oligosaccharides during the synthesis. Keywords: oligosaccharide synthesis, I antigen, carbohydrate mass spectrometry, carbohydrate NMR spectrometry, Gal-GlcNAc oligomers.