| 3JCOCC across O-glycoside linkages of oligosaccharides can provide structural information and are readily interpreted in flexible systems. The present report describes the 3JCOCC torsion angle dependency relevant to an O-glycoside fragment. A range of 13C-labeled model compounds containing C-O-C-C coupling pathways having different structures and dihedral angles (theta) were used to identify structural factors affecting 3JCOCC. Ab initio molecular orbital calculations were utilized to compute 3J COCC for coupling pathways related to those found in saccharides. Experimental and calculated values were in close agreement, thus allowing use of the latter to better define the effect of structure on 3J COCC. Coupling constants of ∼ 3 and ∼ 4 Hz are observed for theta ≈ 0° and 180°, respectively, with minimal coupling (<0.5 Hz) predicted for theta ≈ 90°--110°. The disposition of terminal electronegative substituents along the C-O-C-C coupling pathway also significantly affects 3JCOCC values. A simple Karplus equation for 3JCOCC values is proposed, and applied to analyze trans-O-glycosidic couplings in 13C-labeled methyl beta-lactoside and sucrose.;JCH and JCC values in 2-deoxyribofuranose 1 can provide useful conformational information on the furanosyl ring found in DNA. These values were reported in conformationally-flexible methyl 2-deoxy-beta-D-ribofuranoside 2. In the current study, conformationally-rigid 13C-enriched model compounds, methyl 2-deoxy-alpha-D-arabino-hexopyranoside 3 (North mimic of 1) and methyl 2-deoxy-beta-D- ribo-hexopyranoside 4 (South mimic of 1) were synthesized. JCC and J CH values in 3 and 4 provide a quantitative assessment of the effect of deoxygenation and are validated through comparison to the computationally predicted couplings in 1. Several JCH values are found to be conformation-sensitive in 1. Reported complementarity of the coupling pathways involving the H2R and H2S diastereotopic protons in 1 is reconfirmed in 3 and 4. The correlations drawn between ring conformation and JCH/ JCC magnitude and sign in 1, 3 and 4 will be useful in assessing 2-deoxy-beta-D-ribofuranose ring conformation/dynamics in DNA and in other biomolecules containing ring 1.;13C-Enriched conformationally-rigid alpha-D-[1- 13C]glucopyranosyl 1-phosphate 1 was used to study the effect of O-phosphorylation and ionization state of phosphate on JCH and JCC spin-couplings in carbohydrates. The effect of O-phosphorylation on 2JC1,H2 was significantly large (+210%), while relatively small effects were observed for 1 JCH, 3JCH, 1JCC and 3J CC. Conversion of the mono-anionic to di-anionic form of 1 caused measurable changes in some couplings (1J C1,H1, 1JC1,C2 and 1JC1,H2) but little changes in others (3JC1,H3, 3 JC1H5, 2JC1,C3 and 3JC1,C6). The effects probed here were confined to couplings involving the carbon attached to the phosphorylated oxygen. |
