[Daylan]

Hi, I am doing a reasearch with TAG. I decided to make a derivatization of sn-1,2 DAG and sn-2,3 DAG with 3,5 dinitrophenylisocyanate to yield enantiomers which I can separate by a chiral column in HPLC. My question is if 3,5- dinitrophenyl isocyanate is a chiral or an achiral reagent?
In principe an enantiomer derivatized with a chiral reagent should need to be separated with an achiral column but, could also be separated with a chiral phase HPLC column?

Hope someone han help me.

Thanks

[OC pro]

Any ideas by yourself?

[demoninatutu]

Okay, I'm guessing you don't usually do organic chemistry Daylan. Either way, it is clearly important that you get hold of a basic textbook on organic chemistry and look up chirality.

I must admit I don't work with biomolecules* but we can work a few things out just by looking at the molecules you're working with. First up, is dinitrophenyl isocyanate chiral? A simple rule of thumb in organic chemistry is to look for a carbon that is bonded to four different groups. This by itself might not be enough (the real rule is whether or not the molecule has a symmetry plane) but it's certainly good enough for 3,5-dinitrophenyl isocyanate. If you look up the structure on Google, you'll see that no atom is bound to more than three other atoms. That means that it cannot be chiral.

The next thing to consider is whether or not your derivative will be chiral. For this, you need to understand the reactants, the products and the mechanism of the reaction you're performing. Your reactant, a diglyceride, contains one chiral carbon 'in the middle'. It's chiral because it's bound to four different groups (the two different tails, one short alcohol and one hydrogen). But when you react with 3,5-dinitrophenyl isocyanate, you're modifying the oxygen of the OH group, not the chiral carbon. This means that you won't change the chirality of your reactants by making the derivative with an achiral molecule like 3,5-dinitrophenyl isocyanate. So if you start with enantiomerically pure DAG, you're going to finish with enantiomerically pure DAG.

You only need a chiral column if you're separating enantiomers. This means that if you're starting with a mixture of DAG enantiomers, you will need a chiral column but if you're starting with a pure enantiomer (and I guess you are) then you won't need a chiral column. If you want to use a chiral column on enantiomerically pure products, it should still work, it will at least separate your reactants from your product, but chiral packing is not necessary.

* i.e. I might have misread what you're trying to do.

[Daylan]

Hi demoninatutu,

Thanks for your answer it was very clear.
You are right, I usually do not do organic chemistry. I am now starting in this wonderful area. But I do have some experience.

I was doubting about the chirality of the reactant because I found literature that said that isocyanate derivatizing reactants are chiral.  And also some articles name diastereomers to the DNPU DAG derivatives (form after 3,5 dinitrophenyl isocyanate). And I was in the understanding that Chiral substances derivatized with chiral reagents yield diastereomers. And suddenly the doubt jump in my mind, is then 3,5-dinitrophenyl isocyanate chiral?

I am starting from a mixture of sn-1,2 and sn-2,3 DAG. For this reason I need a chiral column.

Well, I hope everything goes right with my experiment.
Thanks again for your time

[demoninatutu]

I found literature that said that isocyanate derivatizing reactants are chiral

That's certainly not 3,5-dinitrophenylisocyanate itself, more likely the reagent that is being derivatised or even a special chiral derivative of phenylisocyanate.

And also some articles name diastereomers to the DNPU DAG derivatives

It's probably best to go back and check those publications are using simple 3,5-dinitrophenylisocyanate and not something else. If you post the reference, I could look it up and check. I'm guessing it's not directly related to the phenylisocyanate itself, though. As far as I can see, phenylisocyanate is used to make the lipids more soluble in the HPLC solvent.

And I was in the understanding that Chiral substances derivatized with chiral reagents yield diastereomers.

That's true, and it's often done to avoid the need for chiral packing. It's much easier to separate diastereomers.

I am starting from a mixture of sn-1,2 and sn-2,3 DAG. For this reason I need a chiral column.

As I said, I don't work with biomolecules, are sn-1,2 and sn-2,3 DAG terms for two enantiomers? We name things a little differently in organic chemistry.