The relationship between proton–proton NMR coupling constants and substituent electronegativities. II—conformational analysis of the sugar ring in nucleosides and nucleotides in solution using a generalized Karplus equation

Abstract

The relationship between vicinal N M R proton-proton coupling constants and the pseudorotational properties of the sugar ring in nucleosides and nucleotides is reinvestigated. Compared with our earlier study several important improvements are introduced: first, a new empirical generalization of the classical Karplus equation is utilized, which allows an accurate correction for the effects of electronegativity and orientation of substituents on 3J(EIH); second, empirical correlations between the parameters governing the conformation of p-D-furanosides (taken from an analysis of 178 crystal stmctores) were used to define proton-proton torsion angles as a fnnctiou of the pseudorotation parameters P and a,,,; and, third an iterative least-squares computer program was devised to obtain the best fit of the conformational parameters to the experimental coupling constants. N M R data for the sugar ring in the following compounds were taken from the literature and analysed: 3',5'-cy&c nudeotides, a base-stacked nionucleotide, 2'-~ydroarabinonucleosides, or-~-2',2-0-cyclouridine, 2'-and 3'-aminosubstituted ribonucleosides, 2'-and 3'-deoxyribonucleosides. The present results confirm that the conformational properties found in the solid state are, on the whole, preserved in solution.

Toxic Furanoeremophilanes from Senecio bonariensis

“…180°for ␣-substitution in C-1 in agreement with the coupling constant observed. We calculated the vicinal coupling constant J 1,10 of compound 2 with Altona equation (Haasnoot et al, 1981) using the set B of parameters, a dihedral angle of 178°f or steroidal conformation and 156°for non-steroidal conformation. We obtained J ϭ 11.17 Hz for the first conformation and 10.12 Hz for the second.…”

A Karplus equation for 3JHCCN in amino sugar derivatives

“…Fully coupled hydroxyl proton spectra were obtained in this way. However, such spectra were more reliably acquired by use of acetone-d 6 as solvent. On the other hand, in CDCl 3 solution, the presence of a free amino group in derivatives 1 and 7 catalyzed an increased rate of proton exchange of NH 2 and OH groups, thus giving decoupled multiplets that were also good for the purpose.…”

Structural Comparison of Oligoribonucleotides and Their 2′‐Deoxy‐2′‐fluoro Analogs by heteronuclear NMR spectroscopy

“…50:50 equilibrium between C(2')-endo and C(3')-endo for Uf' and ca. 40:60 equilibrium for Cf" (assuming an 8-Hz coupling constant for pure C(Z')-endo and 0 Hz for pure C(3')-endo) [38]. The intermediate size of the coupling constants hinting at the conformational heterogeneity is also observed in unmodified oligomers [2Oa].…”