¹³C−¹H Spin-Coupling Constants in the β-d-Ribofuranosyl Ring:  Effect of Ring Conformation on Coupling Magnitudes

Abstract

Experimental and computational methods have been used to examine the behavior of one-, two-, and three-bond 13C−1H spin-coupling constants (1 J CH, 2 J CH and 3 J 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 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 13C−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.

Extension of the Karplus Relationship for NMR Spin-Spin Coupling Constants to Nonplanar Ring Systems: Pseudorotation of Tetrahydrofuran

“…The inductive effect of an O atom leads to a positive contribution of 1 -2 Hz depending on the position of O and the relative orientation of CO and CH bond [30]. This is also reflected by < [5,67] and frequently utilized to study the conformation of important biological compounds [68]. Table 5) and comparable to the corresponding cyclopentane value of 3.9 Hz ( Table 5).…”

DNA Duplex Dynamics: NMR Relaxation Studies of a Decamer with Uniformly13C-Labeled Purine Nucleotides

“…If vibrational averaging of the CH bond is considered, it becomes about 2% larger (67,68). Ab initio molecular orbital calculations on ␤-D-ribofuranose suggest that sugar conformation affects the r CH value within the 0.01 Å range (69). These studies suggest that a given r CH value may have a 0.01 or a 0.02 Å error, so the relationship between r CH and the motional parameters should be known.…”

New Strategy for the Conformational Analysis of Carbohydrates Based on NOE and 13C NMR Coupling Constants. Application to the Flexible Polysaccharide of Streptococcus mitis J22

“…Serianni and co-workers have pointed out that the 1 J CH values in aldofuranosyl rings depend on C-H bond lengths (42 and references therein), with shorter bonds yielding larger couplings. C-H bond lengths vary with bond orientation with a systematic trend toward shorter lengths when the bond orientation is quasiequatorial and longer bonds when quasiaxial (42) J C1-O4-C4-C3 . The contribution of the first pathway can be estimated theoretically by using the projection sum method (38), while the contribution of the second pathway can be calculated using eq 3.…”