C-13-H-1 spin-coupling constants in the beta-D-ribofuranosyl ring: Effect of ring conformation on coupling magnitudes

Experimental and computational methods have been used to examine the behavior of one-, two-, and three-bond C-13-H-1 spin-coupling constants ((1)J(CH), (2)J(CH) and (3)J(CH), respectively) within the beta-D-ribofuranosyl ring 1 that may be potentially affected by ring conformation. Ab initio molecular orbital (MO) calculations at the HF/6-31G* and MP2/6-31G* levels of theory were employed to assess the effect of ring conformation on molecular parameters (i.e., bond lengths, angles, and torsions) of beta-D-ribofuranose (2) and methyl beta-D-ribofuranoside (3), and these data were validated through comparison to corresponding parameters obtained by X-ray crystallography. The MO-derived structural data were subsequently used to compute (1)J(CH), (2)J(CH) and (3)J(CH) values in 2 as a function of ring conformation. This predicted behavior was then tested experimentally through the measurement of J(CH) values in conformationally-rigid model compounds (aldopyranosides) containing C-13-H-1 coupling pathways similar to those found in specific conformers of 2 and was examined for consistency with previously-derived empirical rules correlating J(CH) With structure in carbohydrates. Available J(CH) data obtained on several biologically-important compounds containing beta-D-ribofuranosyl rings have been interpreted in light of the new correlations with ring conformation.