. Can. J. Chem. 58,631 (1980). Nuclear magnetic resonance properties are shown to be in good accord with those that are expected for synthetic oligosaccharides in the conformations which are predicted by hard-sphere molecular modelling and taking into consideration the important contribution by the exa-anomeric effect. The studies involve first a comparison of the PDG~I(IA~)PDGICNAC (Type I) and p~G a l - On montre que les proprietes de rmn sont en accord avec celles attendues pour les oligosaccharides synthetiques selon les conformations prevues par les modeles spheriques rigides et en tenant compte de la contribution importante de l'effet anomkrique eso. Les etudes impliquent en premier lieu une comparaison des structures des disaccharides ~~Gal(1+3)puGlcNAc (type 1) et p~G a l ( 1 4 4 ) P DGIcNAc (type 2) basee principalement sur les donnees de la rmn du I3C et en second lieu I'ttude des relations existant entre les conformations calc~llees et ies parametres de la rmn du lH et du 13C des determinants du groupe sanguin humain qui derivent du noyau disaccharide de type 1. Parmi les structures examinees on trouve le di, tri et tetrasaccharides pour le ABH et les dtterminants antigeniques de Lewis. On note certaines relations immunologiques-conformationnelles.[Traduit par le journal]

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SynopsisConformational energies of a-and P-D-ghcopyranoses were computed by varying all the ring bond angles and torsional angles using semiempirical potential functions. Solvent accessibility calculations were also performed to obtain a measure of solvent interaction.The results indicate that the 4C1 (D) chair is the most favored conformation, both by potential energy and solvent accessibility criteria. The 4C1 (D) chair conformation is also found to be somewhat flexible, being able to accommodate variations up to 10' in the ring torsional angles without appreciable change in energy. Observed solid-state conformations of these sugars and their derivatives lie in the minimum-energy region, suggesting that the substituents and crystal field forces play a minor role in influencing the pyranose ring conformation.Theory also predicts the variations in the ring torsional angles, i.e., CCCC < CCCO < CCOC, in agreement with the experimental results. The boat and twist-boat conformations are found to be at least 5 kcal mol-' higher in energy compared to the 4C1 (D) chair, suggesting that these forms are unlikely to be present in a polysaccharide chain. The IC4 (D) chair has energy intermediate between that of the 4C1 (D) chair and that of the twist-boat conformation. The calculated energy barrier between 4C1 (D) and lC4 (D) conformations is high-about 11 kcal mol-'.

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