Quaff - 31-10-2017 at 07:42
I'm looking at glyceryl mono-oleate ("GMO"). I see that it has a chiral carbon atom, #2 in the glycerine chain. How can I resolve the isomers ?
I'm thinking to maybe begin with an enantiomeric salt, like d-tartaric acid and react it somehow with the GMO selectively at the 2-position on the
glyceryl carbon. First it would be necessary though, to protect the OH present on the #1 carbon, and realizing that the #2 carbon is sterically
hindered. Maybe I'll have to start with 1,3-glycerly-di-oleate, do the reaction with d-tartaric on the #2 carbon, and subsequently hydrolize off one
of the oleate groups. Obviously, this will be messy. I'm thinking there has to be a better way....
Melgar - 1-11-2017 at 08:01
I'm not sure I follow. Oleic acid, when derived from biological sources, is always the cis isomer, with the double bond at the 9 position. Or are
you referring to the fact that the oleic acid is attached to either the 1 or 2 position on the glycerine molecule? (It seems like the second one.) I
don't suppose any of the reactions with vicinal diols are options? They tend to be irreversible in my experience.
Sigmatropic - 1-11-2017 at 10:01
Perhaps you can start from an enantiomerically pure epichlorhydrin and later on hydrolyse the epoxide.
You're after glycerin with an oleate at the sn1 position, correct?
Quaff - 1-11-2017 at 11:08
Consider glycerine, , 1,2,3 propane triol, that is esterified at one end. Doesn't have to be oleic. Lets use stearic. Glyceryl mono-stearate has
a chiral carbon atom, correct ? Specifically the #2 carbon in the glyceryl moiety. Why ? Because it has four different substituents attached to
it.
I'd like to separate the stereoisomers of a glyceryl monoester
[Edited on 1-11-2017 by Quaff]
unionised - 1-11-2017 at 11:16
Do you know about this sort of thing?
https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/...
If I recall correctly the first chiral chromatography used powdered glucose as the sorbent.
Quaff - 1-11-2017 at 11:26
Thanks ! That is one way that should work. I'm a little leery about chrom. prep. columns, lots of considerations but if as a last resort, yes,
should work.
I'm hoping to come up with a way to do it by crystallization, but every idea I get, I realize its going to be a big mess of a mixture of about 10
different things.
I could make the ketal of the monoester. What would be nice is to run a subsequent hydrolysis to de-ketalize it and have the hydrolysis only produce
one of the isomers.
Maybe start with 1,3-glyceryl di-ester material, and react a chiral acid viz. d-tartaric at the 2-position. Then I could make the sodium salt of the
chiral glyceryl diester tartrate. Then, de-esterify only one of the groups from either the 1 or 3 position. That would leave sodium salt of
d-tartrate at the 2-position and a single ester group at the terminal end of glyceryl chain. But that still leaves having to get the tartrate off
there.
Boffis - 1-11-2017 at 11:28
You are going to require a solid, crystallisable derivative, someone was asking in another thread recently about the preparation of 2,4
dinitro-5-fluoro-l-alanyl-benzene which is used to derivatise and separate amino acid enantiomers. Maybe this would react with the alcohol group on
the glycerol too, the fluorine is very reactive and could probably be made to react with it but like you say you would need to find a way to make it
selective to the 2 position. Given the crowding with two such bulky groups that may be tricky.
Quaff - 1-11-2017 at 11:30
Or, maybe find some naturally occuring glycerly monoester that exists only in either the d or l form, then just do a trans-esterification using the
fatty acid of my choice ? but, where do I find oils in nature that exist in only one stereoisomer ?