Conformations of type 1 and type 2 oligosaccharides from ovarian cyst glycoprotein by nuclear Overhauser effect spectroscopy and T1 simulations.

To probe differences in conformation of the type 1 and type 2 linkages in blood group oligosaccharides, two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY) and 1H T1 data were obtained for two blood group A oligosaccharide alditols containing the type 1 and type 2 linkage. The NOE data were interpreted using a complete relaxation matrix approach. Simulations of NOE and T1 values were made using disaccharide and tetrasaccharide model conformations generated by a systemic variation of the glycosidic dihedral angles phi and psi. NOEs from the amide protons of GlcNAc and GalNAc in the type 1 pentasaccharide alditol were obtained, and simulated in a manner similar to those from carbon-bound protons. In addition to providing data for determining the conformation of the type 1 linkage from amide proton NOEs of GlcNAc and GalNAc to neighboring residues, amide proton NOEs also yield information on the orientation of the acetamido side chains. The amide NOE data indicated subtle differences in the orientation of the amide side chain of GlcNAc among the A type 1 pentasaccharide alditol and two previously studied blood group oligosaccharides, lacto-N-difucohexaose 1 and lacto-N-fucopentaose 1. From the NOE and 1H T1 data, and from simple rigid geometry energy calculations, it is concluded that the type 1 and type 2 linkages in the oligosaccharides studied have different conformations and that these conformations are relatively rigid in solution.