Conformational analysis of natural products

Hetero- and homonuclear coupling constant calculation

Long-range carbon-proton coupling constants: application to conformational studies of oligosaccharides.

Mulloy B, Frenkiel TA, Davies DB; Carbohydr Res 184 (1988) 39-46
PubMed 3242815


3JC,H values have been measured using selective 2D heteronuclear J-resolved n.m.r. spectroscopy for the COCH fragment in various carbohydrates. Measurements on model compounds have been used to characterise a Karplus-type relationship between 3JCOCH and dihedral angles in sugar. The 3JC,H values have also been measured for C-2'-O-2'-C-1-H-1 of sucrose and the sucrose residues in raffinose, stachyose, and melezitose. These values are similar to each other for solutions in D2O and (CD3)2SO and are little affected by the change in solvent, but differ from those predicted from the crystal conformations. The method has been used to correct some assignments in the published 13C-n.m.r. spectrum of melezitose.


Karplus curve

Coupling constant calculation

Karplus-type equations are frequently used to relate vicinal coupling constants, i. e. 3J, to torsion angles. To calculate a coupling constant for a given dihedral angle (θ) enter a value in the form and press Calculate.
To calculate a torsion angle from a coupling constant enter the coupling constant in the 3J field press Calculate. There may be up to four solutions.
The results are shown below!
Torsion angle (θ): °
Coupling constant (3J): Hz