Conformational analysis

Measurement of longrange carboncarbon coupling constants in a uniformly enriched complex polysaccharide.Xu Q, Bush CA; Carbohydr Res 306 (1998) 335339 PubMed 9648243 AbstractA quantitative coherence transfer scheme for 1Hdetected measurement of longrange carboncarbon coupling constants in NMR spectra of complex carbohydrates is described. It is applied to a uniformly highly 13Cenriched monosaccharide and to a complex cell wall polysaccharide from Streptococcus mitis J22 having seven distinct sugars in the repeating subunit. Coupling values within the ring were compared to published values for monosaccharides to demonstrate the validity of the method. An attempt was made to relate coupling constants between carbon atoms across the glycosidic linkage to the dihedral angles of a recently published flexible model for the polysaccharide which is based on 3JCH data. The experimental coupling constants do not agree with any single conformation demonstrating that the repeating subunit of the polysaccharide must be flexible. This conclusion is in accord with results of molecular modeling nuclear Overhauser effect and 3JCH data. Equation^{3}J=2.24*cos^{2}(θ)1.3*cos(θ)+0.5
