Correlation of 13C chemical shifts with torsional angles from high-resolution, 13C-C.P.-M.A.S. N.M.R. studies of crystalline cyclomalto-oligosaccharide complexes, and their relation to the structures of the starch polymorphs

NMR assignment and conformational analysis of the antigenic capsular polysaccharide from Streptococcus pneumoniae type 9N in aqueous solution

Complete 1H and 13C NMR assignments, determined by one- and two-dimensional homo- and hetero-nuclear experiments, are reported for the antigenic capsular polysaccharide (CPS) from Streptococcus pneumoniae serotype 9N (S9 in American nomenclature). Distance constraints derived from 1D NOE difference experiments were combined with energy minimisation (simulated annealing) and molecular dynamics (MD) calculations to determine the most favoured conformation of S9 in aqueous solution at 70 degrees C. NOE values simulated for several static conformational models using the NOEMOL program did not correlate well with experimental values, whereas time averaged interproton distances calculated from 500 ps of restrained MD (using the Tropp formalism to account for rapid internal mobility) were in close agreement with experimentally derived distance estimates.

Influence of sulfate and carboxylate groups on the conformation of chondroitin sulfate related disaccharides

1H NMR and 13C NMR spectral parameters of eight sulfated uronic acid containing disaccharides 1-8 were used to determine the conformational preferences that depend on the pattern of sulfation. Three sulfated derivatives of benzyl beta-D-Gal-(1-->4)-beta-D-GlcA (1), its 6'-sulfate 2, 4'-sulfate 3, and 4',6'-disulfate 4 were used as models for the beta-(1-->4) glycosidic linkage of chondroitin sulfates and three sulfated derivatives of benzyl beta-D-GlcA-(1-->3)-beta-D-Gal (5), its 6-sulfate 6, 4-sulfate 7, and 4,6-disulfate 8 were used as models for the beta-(1-->3) glycosidic linkage of chondroitin sulfates. To determine the dependence of conformational preferences on the charged groups, the sulfated disaccharides 2, 3, and 4 were compared to their unsulfated parent compound 1, and 6, 7, and 8 were compared to their parent compound 5. The 3JH-5,H-6 coupling constants were determined by high-order analysis of the spin systems, and from these the preferred populations of the hydroxymethyl groups were calculated. Selective 1D NOEs and ROEs were measured from H-1' across the glycosidic linkage to obtain the average distance of the protons adjacent to the glycosidic linkage. Derivatives of beta-D-Gal-(1-->4)-beta-D-GlcA carrying a sulfate group in the 6'-position (2) and in the 4'- and 6'-position (4) show a slight repulsive effect between the 6'-sulfate groups and the carboxylate group as expressed in small changes of the preferred populations of the glycosidic linkage and the sulfonyloxymethyl group. The 4-sulfate groups in 3 and 4 do not show a significant influence on the glycosidic linkage. However, the two sulfate groups in 4 exhibit a repulsive effect leading to a very high population of the gt conformation of the sulfonyloxymethyl group. In contrast hereto, the sulfate group at C-4 of beta-D-GlcA-(1-->3)-beta-D-Gal disaccharides 7 and 8 and the carboxylate group exert an attractive interaction that leads to a change of the conformation of the glycosidic linkage in 7 and 8 by about 30 degrees. The 6-sulfate groups of the disaccharides 6 and 8 show a slight repulsive interaction with the carboxylate and/or 4-sulfate group. Changes in 13C NMR chemical shifts support the interpretation obtained from the NOE and ROE analysis.(ABSTRACT TRUNCATED AT 400 WORDS)

13C-CP/MAS NMR studies of the cyclomalto-oligosaccharide (cyclodextrin) hydrates

The 13C-CP/MAS NMR spectra of cyclomaltohexaose (alpha-cyclodextrin) hexahydrate, cyclomaltoheptaose (beta-cyclodextrin) "undecahydrate", cyclomalto-octaose (gamma-cyclodextrin) "octadecahydrate", and of the same materials at lower levels of hydration are compared with solution NMR data, structures obtained from single crystal diffraction studies, and with previous reports of the 13C-CP/MAS NMR spectra. The chemical shifts of the C-1 and C-4 resonances can be correlated with the conformation about the (1----4) linkage. The chemical shifts of the C-6 resonances are also sensitive to hydrogen-bonding interactions, as shown by the spectral changes on loss of water from the structures. The results suggest that, for resonances of carbon atoms close to a centre of significant conformational change, chemical shifts may be predicted on the basis of conformation alone, but for the resonances of more distant atoms, changes in chemical shift due to conformational change may be masked by the effects of alterations in the local environment.

N.m.r. and conformational analysis of the capsular polysaccharide from Streptococcus pneumoniae type 4

The 1H- and 13C-n.m.r. data on the capsular polysaccharide (1) produced by Streptococcus pneumoniae type 4, the depyruvated polysaccharide (2), and a tetrasaccharide (3a) derived by Smith degradation of 2 were used as constraints on a computer-generated model of the conformation of 1 and to assess the effects of the pyruvic acetal substituent on the conformation. The dynamics of the polysaccharide systems and the influence of the pyruvic acetal were investigated using 13C-n.m.r. relaxation measurements.