Structural Stability of Scyllo vs Myo Inositol

[bomba923]

Scyllo-inositol should be more stable than myo-inositol, right? (unless I'm missing a certain detail)

But in nearly all literature on inositols, it is always myo-inositol that is primarily focused on. Scyllo-inositol is said to exist in "trace amounts" along with other inositols, while myo-inositol is the most common of all inositols. Also, Wikipedia does not mention scyllo-inositol (only myo-inositol) (see). In general, it seems scyllo-inositol (which I think is the most stable of all inositols) is barely mentioned in inositol literature.

Perhaps myo-inositol is more "useful" nutritionally and otherwise than scyllo-inositol.
But is also more structurally stable than scyllo-inositol??

(Edit: for those who don't know, inositol (C₆H₁₂O₆) is a structural isomer of glucose; its IUPAC
name would be 1,2,3,4,5,6-cyclohexanehexol. See the attached image for more information)

 

[Gokul43201]

Wow, it must be over a year since you started thinking about the inositols! Are you making a project out of their study?

As for stability, I'm not as clever (or brave) as you, when it comes to deciding which isomer is more stable. I need to at least see a 3D rendering of the structure before I can make up my mind. It may very easily be (in my judgement, at least) that the steric hindrance is more than made up for by H-bonds between nearby hydroxyl groups.

 

[bomba923]

Wow, it must be over a year since you started thinking about the inositols! Are you making a project out of their study?

Not really; I thought of them last year when I took organic chemistry at a local community college (as a HS junior), and was looking for a simple organic molecular compound with a high melting point (remember this thread?). Immediately, I thought "carbohydrates", and thus, "glucose"; however, I thought there may be a more...optimal/simpler...way of arranging C₆H₁₂O₆ and find that (optimal) compound; simply make a six-carbon ring, and attach one hydroxyl to each carbon! And thus, I found "scyllo-inositol".

I need to at least see a 3D rendering of the structure before I can make up my mind. It may very easily be (in my judgement, at least) that the steric hindrance is more than made up for by H-bonds between nearby hydroxyl groups.

Using ACD ChemSketch, I have some basic (not high quality) 3D rendering of http://www.trc-canada.com/product.lasso?product=I666050 and myo-inositol (see the attached images), and updated my original image .

*But back to the original question :shy::
Scyllo-inositol is more stable than myo-inositol, right?

 

[Gokul43201]

From the 3D rendering and additionally,from the melting points, it seems highly likely that there is H-bonding between hydroxyl groups that stabilizes the myo- isomer.

 

[bomba923]

From the 3D rendering and additionally,from the melting points, it seems highly likely that there is H-bonding between hydroxyl groups that stabilizes the myo- isomer.

Certainly the myo- isomer can be stable...but that does not necessarily make it lower in energy (more stable) than the scyllo- isomer :shy:. Though, I suppose, interconversion between inositol stereoisomers is quite possible if the energy barrier is small enough (but I don't have that information! If I did, my question here would already be answered ).

But anyway, out of all inositol (stereo)isomers, the scyllo- isomer is the lowest in energy (most stable), right?

 

[Cesium]

I would guess that scyllo-isomer would be more stable too. I'm really bad at stereochemistry though. Interesting compounds though- thanks for posting their structures. Are they synthesized from sorbitol by any chance? They look like "cyclosorbitol".

Edit: Sorbitol, mannitol, xylitol are all isomers of C6O6H14- just ignore me.

 

[bomba923]

Interesting compounds though- thanks for posting their structures. Are they synthesized from sorbitol by any chance? They look like "cyclosorbitol".

*http://en.wikipedia.org/wiki/Inositol
Inositol is synthesized from G6P (glucose-6-phosphate) in two steps. First G6P is isomerized by INYNA1 to myo-inositol 1-phosphate, which is then dephosphorylated by IMPA1 to yield inositol.

Edit: Sorbitol, mannitol, xylitol are all isomers of C6O6H14

...Except for xylitol (C₅H₁₂O₅)

I would guess that scyllo-isomer would be more stable too.

But also (as I think) the most stable of all inositol stereoisomers, right?

 

[Gokul43201]

But anyway, out of all inositol (stereo)isomers, the scyllo- isomer is the lowest in energy (most stable), right?

I wouldn't be surprised if the myo- isomer was more stable. Intramolecular H-bonding stabilizes the molecule. There is more of this in the myo- isomer (indirect evidence for this is its lower mp).

 

[gravenewworld]

Do you have access to a computational chemistry package such as Gaussian? Gaussian would be perfect for this little question of yours. You could simply write in the coordinates for the atoms of your molecule, do a geometry optimization and see what optmized geometry of the molecule would be. Gaussian can even calculate the energies in hartree focks of the isomers you are talking about which may explain why one is favored over the other.

 

[Alquimista180]

...Except for xylitol (C₅H₁₂O₅)

But also (as I think) the most stable of all inositol stereoisomers, right?

Dear Sir,

In the following quote "*http://en.wikipedia.org/wiki/Inositol
Inositol is synthesized from G6P (glucose-6-phosphate) in two steps. First G6P is isomerized by INYNA1 to myo-inositol 1-phosphate, which is then dephosphorylated by IMPA1 to yield inositol.", I would like to know the meaning of INYNA1.
The meaning of IMPA1, I have found out, "inositol(myo)-1(or 4)-monophosphatase1", but for the abbreviature INYNA1 I have not found out anything!
Could you help me?

 

[chemisttree]

You will find that there is one more axial interaction with the myo than the scyllo compound. Draw the compound as a chair configuration and notice that the scyllo compound has OH groups at equatorial positions. The myo compound has at least one axial OH that interacts with two other protons in axial positions.

You can see it in your 3-D picture.

Stability is not the source of interest in the molecule. Things like myo's association with depression, panic disorder, OC disorder, alzheimer's and so forth form the basis of that focus. The presence of the much rarer scyllo isomer is only interesting as it relates to the inhibition of the uptake of the myo isomer...

Melting points are generally more related to the regularity in the structure rather than differences in energy or biological usefulness of the compounds.