From: Soren R. Jensen (oksrj$##$pop.dtu.dk)
Date: Tue Dec 14 1999 - 11:02:26 EST
Dear Luis,
Note that in aq. solution, you can also expect the aldehyde groups to be
hydrated. I am not sure how much that will contribute, but a compound like
secologanin is almost 50% hydrated in water as seen by NMR.
By the way, I remember a paper (I believe it was in JACS) about 15 years ago
on an NMR study of glucose in aq solution. Good luck - Soren
At 14:43 13-12-99 +0100, you wrote:
> Dear all,
> My problem is basically what follows: I have done the oxidation of the
>alcoholic group in C6 of D-glucose to the aldehyde form. The newly formed
>compound has now two aldehyde functions. As a consequence of the presence
>of the remaining OH groups of the sugar squeleton, several forms might
>coexist in equilibrium in water. Thus, the sugar can addopt two basic
>pyranose hemiacetal structures, depending on whether it is closed over the
>C1 or the C6 aldehyde groups (--C5-O-C1--, or --C2-O-C6--). Furthermore, in
>every form it exists still the chance to form the alpha or beta anomers. We
>should also think that besides the pyranose forms, furanose rings might
>also be present in the equilibrium, together with the opened form of the
>sugar.
> The fact is that I would like to determine the contribution of one of
>these forms to this equilibrium in water, and I do not know exactly how to
>approach the problem. I have already thought about several possibilities,
>but none of them seems to be completely suitable:
> 1) Trap all the forms in equilibrium by a rapid reaction, let us say
>permethylation with MeI, and then separate and/or quantitate the
>contribution of every form. However, I do not know whether there is any
>reaction fast enough as to allow to do such thing without modifying at the
>same time the equilibrium (the reaction has to work in water on the other
>hand).
> 2) Studying the equilibrium by NMR might be easier, but when I see the
>1H-NMR and specially 13C-NMR of this compound I feel really discouraged.
>
> Does anybody have any suggestion about how to solve this problem??
>
> Well, that is all, thank you very much in advance for any commentary or
>suggestion. Have a very good day!!
>
>
>==========================
============
>Luis Fernando García Alles, Ph.D.
>Departement für Chemie und Biochemie
>Universität Bern
>Freiestrasse 3
>CH-3012 Bern, Schweiz
>Tel. ++41 (0)31/631 37 92
>Fax ++41 (0)31/631 33 83
>E-mail :garcia$##$ibc.unibe.ch
>==========================
============
>
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>
Soren Rosendal Jensen
Dept. of Organic Chemistry Email oksrj$##$pop.dtu.dk
Techn. University of Denmark Fax +45 4593 3968
DK-2800 Lyngby, Denmark Tel +45 4525 2103
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