I am wondering, if it is possible to have multiplate and doublet of doublet anomeric protons in polyphenol glycosides? If possible then in what case? Usually, alpha- and beta- configurations of sugar attachments are determined through J-couplingvalue but J value is absent in multiplate anomers whereas there are two J values present for doublet of doublet anomer. So how can we determine the alpha- or beta- configuration of sugar.
I am looking forward its answer with literature references.
Yes, it is possible, in multiple variations. One possibility is a 2-deoxy sugar.
You may have to do more NMR work, including 2D/NOE based experiments.
Jacek is right, 2-desoxy Sugars may give two distinctly different coupling constants, at least in the 1-H axial orientation.
I have few other possiblities to offer :
if 1-H is equatorially oiented there may also be an obvervable 4JHH coupling (called "W-coupling".
N-acylated (acetylated) 2-Aminosugars sometimes have sitinct orientation(s) of the amide bond which may give two signal sets for the 1H (may loog like "dd" but is d + d).
In a very well resolved cosy spectrum you may distinguish both, couling will give two
correlations to two different protons, diastereotopic splitting will show one correlation to another Proton, which might be also a liittle differentiated (but has integral value of 1)
As you mention polyphenols which in your case are glycosylated, hindered rotation as well as classical stereocenters may induce a diastereotopic split, well known for e.g. sterically hindered bi-Phenyls
the least probable explanation is a mixture of alpha and beta anomers in your sample, where by chance both orientations have accidentically the same chemical shift. Not totally impossible, however...
Thank you Jacek Martynow and Herbert Kogler for the possibility answer. And there it is true that I am talking about 2-deoxy sugar conjugation for sure. I do not have much NMR analytical concepts beside referential elucidation. I would more appreciate some literature references so that I can go through it and grasp some important information as explained by Herbert Kogler.
In addition to this, as you explained in the last sentence, the NMR sample probably have mixture of alpha and beta anomers. Possible, but I was wondering how could I explain the situation and say the exact alpha or beta orientation of sugar attached to aglycon. Since one anomer has J value more then 8 Hz and another has less then 2 Hz.
Dear Prakash Parajuli
If you know about a 2-desoxy sugar you now have a start. H-1 has one large and one small culpling constant. If you assume a pyranose (6-membered ring and not 5-membered furanose) and an chair conformation, then the large coupling constant indicatesa a 1-H-axial-2-H-axial orientation. if you draw the stereostructure you will immediately recognise the 180 deg vicinal angle between both protons.
Unfortunately in most positions you have only one Proton and only the bis-axial orientation is indicated by a large coupling constant, all other combinations,
axial-eqatorial
eqatorial-axial
equatorial-equatorial are leading to small coupling constants as the angle between poth Protons as seen along the carbon backbone is around 60 deg.
But you can find other axially oriented Groups in your pyranose chair, provided you have one axial Proton (in your case the H-1) by NOE. The 1.3 positions are bis-axially
and in spatial proximity so you may get a good correlation to H-3 (if axially oriented) or H-5 (or 6-CH2) whichever is axial. Fron the axial proton at C-2 (the one with the large coupling constant to H-1) you may find substituents on the opposite side of the ring, which are also axially oriented. In all other cases assume the eqatorial orientation of the Protons and you get the relative stereochemistry of your sugar.
The Alpha and beta Notation of the anomer refers to the relative orientation of the two substituents at the ether-link with the lowes priority according to the CIP notation.
For aldoses in the pyranoid form this is H-1 and H-5.If both are axially oriented (H-1 and H-5 with a significant NOE effect), they are on teh same side of the molecular plane and the sugar is in ist beta form otherwise it is Alpha.
unfortunately I read only german textbooks where this procedure is quite well described. In an old textbook on 2D NMR edited by Croasmun and Carlson (Wiley 1994) there is a chapter written by Dabrowski on the Analysis of carbohydrates in most parts still up to date. and in english
Thank you very much Herbert Kogler for your explanation regarding NMR elucidation. I think I will get the answer of my question from your reference.
I just want to mention one detail for you, Prakash. If you are not certain about if there is a mixture of anomers or not, just run a quality analytical HPLC (C-18?) of your glycoside. That should answer your doubts easily.
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