~(13)C-~1H Spin-Coupling Constants in the β-D-Ribofuranosyl Ring: Effect of Ring Conformation on Coupling Magnitudes

摘要

Experimental and computational methods have been used to examine the behavior of one-, two-, and three-bond ~(13)C-~1H spin-coupling constants (~1J_(CH), ~2J_(CH) and ~3J_(CH), respectively) within the β-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 β-D-ribofuranose (2) and methyl β-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 ~1J_(CH), ~2J_(CH) and ~3J_(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 ~(13)C—~1H 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 β-D-ribofuranosyl rings have been interpreted in light of the new correlations with ring conformation.