Conformational analysis of ribonucleosides from proton-proton coupling constants.

A graphical method is described which permits the determination in solution of conformational equilibria and parameters of ribonucleosides from proton-proton coupling constants. The method is based on the pseudorotational concept and the use of the Karplus equation. Using a large number of 1H-NMR data on ribonucleosides from the literature, on optimal set of Karplus constants, A = 10.0, B = -1.2, was obtained. It is shown that this set of Karplus constants, in connection with the pseudorotational treatment, describes satisfactorily the nucleoside conformations, especially the pucker amplitude. The solution results are compared with X-ray data and the differences are discussed. The method can be used either graphically or by direct computer treatment of the data.