Part II. Using NOE to differentiate between the two diastereoisomeric glycosides heterodendrin and epi-heterodendrin.

Philips Dannie
Rayat Sundeep
Sen Subhabrata
 

Reference:
Lankhorst, P. P.; Smeets, J. W. H., Haasnoot, C. A. G. Carbohydrate Research 1994, 269,17-27.



Introduction


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 diastereomers. This was further confirmed by molecular mechanics.



Questions:


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. Explain.