Using NOE to differentiate between the two diastereoisomeric
glycosides heterodendrin and epi-heterodendrin.
Lankhorst, P. P.; Smeets, J. W. H., Haasnoot, C. A. G.
Carbohydrate Research 1994, 269,17-27.
In this paper the researchers have described the application of NOE
and molecular mechanics to distinguish between the two
diastereomeric glycosides heterodendrin and epi-heterodendrin.
The proton NMR of the two diastereomers differ mainly in the chemical
shift of the H2 in the side chains. However it did not
gave any stereospecific information. Nevertheless the NOE experiment
on a time average basis helped in discriminating between the two
This was further confirmed by molecular mechanics.
The structure of two diastereoisomeric glysosides heterodendrin
and epiheterodendrin are shown in the following picture.
1) Assign each diastereomer to the proton spectra shown.
2) Does your assignment agrees with the structure and what is the major
differences in the 1H NMR of the two diastereomers?
3) Considering the NOED spectra, what can you
say about the stereospecificity of the molecule?
4) Explain the NOED spectra for both the isomers? Support your answer
with proper justification.
5) Does the deuteration of the concerned protons effect the NOED.