[marthaj]

HI
I'd like to ask you if this is possible to use carbodiimide in water like solvent.
I think that carbodiimide hydrates to urea, but if the solvent is water, the reaction will need a lot of carbodiimide.
Please, help because I am observing coupling reactions in water using carbodiimide like reagent.
Thank you

[Doc Oc]

You're correct, you can't use water because it will destroy the DCC.  DMF is a common choice for these types of couplings, although I've also used THF, dichloromethane, and acetonitrile.

[marthaj]

Thank J-bone
I am confused,  in the next paper they use carbodiimide in water:

Carbodiimide-mediated covalent attachment of lysine to wheat gluten and its apparent digestibility by penaeid shrimp (J. Agric. Food Chem., 1995, 43 (3), pp 733–737).

I dont know what is wrong ?
Also I coupled lysine in a resin just using HObT/DCC in a mixture of DMF/WATER (50:25)
The results show that this worked.

[marthaj]

J-Bone, can you please recommend me a solvent to make the polymerization of lysine by using DCC/HOBt?
Thanks

[Doc Oc]

If you've already done this coupling in DMF/water, why are you hesitant to do it again?  If it worked then use it.  Like I said, DMF is very common in peptide couplings so I would say you can default to that if you're unsure.

What are you coupling the lysine to?

[marthaj]

Thanks J-Bone
I coupled lysine with a hydroxyl resin.  Just I want to explain why the reaction worked  although the theory says that DCC doesnt work in water.

[Doc Oc]

I see.  Well, I gave a brief glance at that J. Agric. Food Chem. paper and it looks like water was used to solubilize the gluten.  DMF is very miscible with water so this solvent system is favorable for that peptide coupling with EDC.  But depending on the hydroxyl resin you used, water may not be necessary at all.  Remember that the nitrogen in DMF can still hydrogen bond with water and there's a 2:1 ratio of DMF to water, so that could be why the DCC wasn't hydrolyzed.  Of course, this is all speculation and I don't know for certain, just trying to make sense of the information I have.

[marthaj]

Thank you J-bone.. thanks for the help..